JP2005181967A - Drive device for organic el display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain fine linearity in the case of displaying a half tone by pulse width modulation (PWM), even when an image is displayed at a luminance lower than that at normal display. <P>SOLUTION: In the normal display, a signal electrode driver makes a 1st constant current to flow from a signal electrode into a scanning electrode of a selected line. A scanning electrode driver sets potential at the time of non-selection to V<SB>CH1</SB>. When displaying at luminance lower than that of normal display, the signal electrode driver makes a 2nd constant current smaller than the 1st constant current to flow, from the signal electrode to the scanning electrode of the selected line. Since the potential of the signal electrode is lowered, as compared with that of normal display time, the potential at the non-selection is set to V<SB>CH2</SB>which is lower than that of normal display. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a drive device for an organic EL (Electroluminescence) display device.

  An organic EL element has an organic thin film between an anode and a cathode. Even if a voltage is applied between both electrodes so that the cathode has a higher potential than the anode, almost no current flows through the organic thin film, and the organic thin film does not emit light. Conversely, when a voltage equal to or higher than a predetermined voltage (light emission start voltage) is applied between the two electrodes so that the anode has a higher potential than the cathode, a current flows through the organic thin film, and the organic thin film emits light. An organic EL display device using this light emission is known.

  In an organic EL display device, for example, a plurality of scanning electrodes and a plurality of signal electrodes are arranged so as to be orthogonal to each other with an organic thin film interposed therebetween. In such an organic EL display device, the intersection of each scanning electrode and each signal electrode emits light as a pixel. Further, the pixels are arranged in a matrix. In this case, the organic EL display device is driven by line sequential driving. That is, each scan electrode is sequentially selected, and a current is passed from the signal electrode to the selected scan electrode in accordance with the display data of the selected row.

As a driving method of an organic EL display device by line sequential driving, for example, driving methods described in Patent Documents 1 and 2 are known. In the driving method described in Patent Document 1, when the selected row is switched, all the scanning electrodes and all the signal electrodes are set to a predetermined reset potential, and then the next row is selected. FIG. 14 shows an example of a driving waveform in the driving method described in Patent Document 1. The solid line shown in FIG. 14A is the drive waveform of the scan electrode of the Lth row, and the solid line shown in FIG. 14B is the drive waveform of the scan electrode of the next row (L + 1th row). Moreover, the broken line shown in FIG. 14 is a drive waveform of one signal electrode. As shown in FIG. 14, each row is set to the potential V _SS when it is selected, and is set to the potential V _CH while the other rows are selected. However, the relationship V _SS <V _CH is established. The constant current is driven to flow the scan electrodes of the selected row from the signal electrode of the pixel to emit light, so that the potential of the signal electrode becomes higher than the V _SS potential. Then, between the end of the selection period and the start of the next selection period, the potential of each scan electrode and each signal electrode is set to a reset potential (V _{SS in the} example shown in FIG. 14). Note that the reset potential is a potential for discharging the charge accumulated in the pixel by applying a reverse bias voltage. By driving in this way, the charge accumulated in the pixel by applying the reverse bias voltage is discharged, and the rise time from the start of the selection period until the pixel emits light is shortened. The reverse bias is that the level relationship between the potential of the signal electrode and the potential of the scanning electrode is opposite to that when the pixel emits light.

In the driving method described in Patent Document 2, the potential of each signal electrode is set to the reset potential from the end of the selection period to the start of the next selection period. Also, during this period, it until the potential of the scanning electrode is selected is set to V _CH, the other scanning electrodes is set to the reset potential V _SS. By driving in this way, the rise time until the pixel emits light can be shortened and the life of the organic EL element can be extended. Further, in Patent Document 2, from the end of the selection period to the start of the next selection period, the potential of the scan electrode to be selected next is set to _VCH, and the potentials of the other scan electrodes are set to the reset potential V _SS. A driving method is also described. Also, during the period from the end of the selection period to the start of the next selection period, the potential of the scan electrode selected so far and the next scan electrode to be selected are set to _VCH, and the potentials of the other scan electrodes are reset. A driving method for setting the potential to _VSS is also described.

  In some cases, the organic EL display device displays a halftone. As a halftone display method, a pulse width modulation method (PWM) is known. In PWM, the gradation is changed by changing the ratio of the light emission time of the pixel in the selection period (the ratio of the time during which a constant current is passed from the signal electrode to the scanning electrode in the selected row).

  Patent Document 3 discloses a display panel that outputs a constant current source drive voltage to a signal electrode in a normal state and outputs a voltage lower than the constant current source drive voltage to the signal electrode when a display with the minimum luminance is set from the outside. A drive device is described.

Japanese Laid-Open Patent Publication No. 9-232074 (page 2-7, FIG. 1-15) JP 2003-295823 A (page 4-9, FIG. 1-10) JP 2002-91378 A (paragraphs 0014-0024, FIGS. 1-3)

  In a display device or the like of an in-vehicle navigation system, switching is performed so that an image is displayed with high luminance when the surroundings are bright and an image is displayed with low luminance when the surroundings are dark. In such switching, display with high luminance is referred to as normal display. A display with low luminance is referred to as a dimming display. It should be noted that halftone can be displayed by PWM in both normal display and dimming display.

  When switching to dimming display, the constant current value flowing in the organic EL element may be lowered. By reducing the constant current value, the potential of the signal electrode during dimming display becomes lower than during normal display. The drive waveform shown in FIG. 14 is assumed to be a drive waveform during normal display. FIG. 15 shows an example of a drive waveform when the constant current value is lowered to switch to the dimming display in the drive method described in Patent Document 1. Similarly to the solid lines shown in FIGS. 14A and 14B, the solid lines shown in FIGS. 15A and 15B show the drive waveforms of the scan electrodes in the Lth row and the (L + 1) th row, respectively. Further, the broken line shown in FIG. 15 shows the driving waveform of one signal electrode, similarly to the broken line shown in FIG. The signal electrode potential during dimming display (FIG. 15) is lower than the signal electrode potential during normal display (FIG. 14).

Dimming result of switching the display, when the potential of the signal electrode is reduced, the potential difference between the potential V _CH of the scanning electrodes that are not selected and the signal electrode potential increases. In this case, a phenomenon occurs in which the potential of the signal electrode at the start of the selection period becomes higher than the potential to be originally set, and then decreases to the original potential (see FIG. 15). The reason for this will be described. Immediately before the start of the selection period, each scanning electrode and each signal electrode are both set to a reset potential (in this example, V _SS ). At this time, the potential difference between one signal electrode and each scanning electrode is 0V. Thereafter, when the selection period is started, the potential of each scan electrode other than the selected row is set to _VCH , and the signal electrode is set to a potential lower than _VCH . However, since one signal electrode forms a capacitor with each scanning electrode, and the potential difference immediately before the start of the selection period is 0 V, the potential of the signal electrode is not limited even if the potential is set to the signal electrode. is, it becomes to such a value as close to the V _CH. Therefore, the potential of the signal electrode becomes higher than the potential that should be originally set at the start of the selection period, and then drops to the original potential. This phenomenon, the larger the difference between the potential and the potential V _CH of the signal electrode in the selection period, remarkable.

  Thus, if the potential of the signal electrode changes during the selection period, good linearity cannot be obtained when displaying a halftone by PWM. That is, the method of changing the luminance between gradations is not constant, and good display quality cannot be maintained. This problem occurs not only in the case of the driving method described in Patent Document 1, but also in the driving method described in Patent Document 2.

  Therefore, an object of the present invention is to obtain good linearity when displaying a halftone by PWM even during dimming display.

  Aspect 1 of the present invention is a driving device for an organic EL display device in which an organic thin film is disposed between a plurality of scanning electrodes and a plurality of signal electrodes, and scanning of the scanning electrodes is performed while selecting individual scanning electrodes. And a signal electrode driver for causing a constant current to flow through the organic thin film on the scan electrode selected from the signal electrode in which the pixel to be lit is present, and the signal electrode driver includes the first constant current When a second constant current having a current value lower than that of the first constant current is passed and the scan electrode driver causes the signal electrode driver to pass the first constant current, the selected scan electrode is set to the potential at the time of selection and selected. When the scan electrode that has not been set is set to the first non-selection potential and the signal electrode driver passes the second constant current, the selected scan electrode is set to the selection potential and the scan electrode that is not selected is 1 non-selected time train To provide a driving device of an organic EL display device and setting the second non-selection period potential lower than.

  According to the second aspect of the present invention, in the first aspect, the voltage for setting the scan electrode to the first non-selection potential and the voltage for setting the scan electrode to the second non-selection potential are output to the scan electrode driver. And a control means for controlling switching of a constant current supplied by the signal electrode driver and switching of a voltage output from the power supply circuit to the scan electrode driver. The control means supplies the first constant current to the signal electrode driver. In the case of causing the current to flow, the power supply circuit outputs a voltage for setting the scan electrode to the first non-selection potential, and in the case of causing the signal electrode driver to pass the second constant current, A voltage for setting the non-selection potential is output, and the scan electrode driver sets the potential of the unselected scan electrode to the first non-selection potential or the second non-selection potential according to the voltage output from the power supply circuit. Selection potential To provide a driving device of an organic EL display device to be set.

  Aspect 3 of the present invention includes a capacitor in which one electrode is connected to a constant voltage and a signal in which a first constant current or a second constant current flows in a selection period of each scan electrode. When the change in the potential of the electrode has subsided, connect at least one of the signal electrodes to the other electrode of the capacitor, and charge the capacitor according to the potential of the signal electrode connected to the other electrode. Connecting means for storing, and the capacitor outputs a voltage corresponding to the accumulated charge to the scan electrode driver, and the scan electrode driver sets the potential of the scan electrode not selected according to the voltage output by the capacitor. Provided is a drive device for an organic EL display device which is set to a first non-selection potential or a second non-selection potential.

  Aspect 4 of the present invention includes a voltage output unit that outputs a voltage that linearly changes in accordance with a current value of a constant current that flows through the signal electrode in aspect 1, and the scan electrode driver includes a voltage output unit. A drive device for an organic EL display device is provided that sets the potential of a scan electrode that is not selected to a first non-selection potential or a second non-selection potential in accordance with the voltage output from the.

Aspect 5 of the present invention is the signal electrode driver according to any one of aspects 1 to 4, wherein the light emission start voltage of the organic thin film is V _p [V], the current value of the second constant current is I ₂ [μA], The potential of the signal electrode when the second constant current is caused to flow is V _s2 [V], the length of the selection period is t [μs], and the sum of the capacitances of the pixels existing in one signal electrode is When C [nF] is selected, the selection potential is V _SS [V], and the second non-selection potential is V _CH2 [V], the second non-selection potential V _CH2 is V _s2 −V _p <V _CH2 , V _SS + V _p <V _CH2 , and V _CH2 ≦ V _s2 + (I ₂ · t · 0.5 / C) · 10 ⁻³ drive device for organic EL display device satisfying conditions To do.

  According to the driving apparatus for an organic EL display device according to any one of claims 1 to 4, the potential difference between the potential of the signal electrode through which the second constant current flows and the second non-selection potential can be reduced. it can. Therefore, it is possible to prevent the phenomenon that the potential of the signal electrode becomes higher than the potential to be originally set at the start of the selection period, and then drops to the original potential. As a result, it is possible to maintain good linearity when performing halftone display with PWM.

  According to the drive device for the organic EL display device according to claim 5, it is possible to maintain good linearity when performing halftone display with PWM, and it is possible to prevent light emission of pixels in non-selected rows, Furthermore, the pixels in the selected row can be made to emit light more reliably.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following description, the unit of potential and voltage is V (volt) unless otherwise specified.

[First Embodiment] FIG. 1 is a block diagram showing an example of a driving device for an organic EL display device according to a first embodiment of the present invention. An organic EL display device (hereinafter referred to as a display panel) 1 includes a plurality of scanning electrodes (not shown) and a plurality of signal electrodes (not shown). Each scanning electrode and each signal electrode are arranged so as to be orthogonal to each other with the organic thin film interposed therebetween. The intersection between each scanning electrode and each signal electrode is a pixel. In each pixel, when an electric current flows from the signal electrode side to the scanning electrode side, the organic thin film of the pixel emits light.

  The display panel 1 performs both normal display and dimming display according to a drive device (a drive device including the controller 2 and the like). Also, halftone display by PWM is performed during normal display and during dimming display.

  In the following description, the constant current that flows through the light emitting pixel during normal display is referred to as a first constant current. In addition, a constant current flowing through the light emitting pixel during dimming display is referred to as a second constant current.

  In the following description, the selection potential is a potential set for the scan electrode selected during the selection period. The non-selection potential is a potential set for each scan electrode that is not selected during the selection period of a certain scan electrode.

The drive device includes a controller 2, a scan electrode driver 3, a signal electrode driver 4, and a power supply circuit 5. The controller (control means) 2 includes a memory _2a for storing image data to be displayed. The controller 2 displays an image on the display panel 1 by controlling the scanning electrode driver 3, the signal electrode driver 4, and the power supply circuit 5.

Further, an external MPU (Micro Processing Unit) 6 is connected to the controller 2. The external MPU 6 instructs the controller 2 to perform normal display or dimming display. Further, the external MPU 6 performs a process of rewriting display data stored in the memory _2a .

  The display data includes data indicating any one of the gradations from the highest luminance to the lowest luminance corresponding to each pixel. Thus, the display data includes pixel data indicating a halftone. Even when switching between the normal display and the dimming display, the external MPU 6 does not change the display data if the display content is not changed. In this case, however, the display content does not change, but the brightness of the displayed image changes.

The scan electrode driver 3 selects each scan electrode one by one in accordance with the controller 2 and sets the potential of the scan electrode in the selected row and the non-selected row. Then, the scanning electrode is scanned while selecting each scanning electrode. A voltage for setting the potential of each scan electrode is supplied from the power supply circuit 5. The scan electrode driver 3 sets the scan electrode of the selected row to the selection potential (V _SS ). Further, during the selection period of a certain scan electrode, the potentials of the other scan electrodes are set to the non-selection potential. However, the non-selection potential differs between normal display and dimming display. Unselected period potential and V _CH1 during normal display, the non-selection time potential during dimming displays and V _CH2.

  The signal electrode driver 4 causes a constant current to flow from the signal electrode in which the pixel to be lit exists to the selected row scanning electrode during the selection period according to the controller 2 and the display data of the selected row. That is, the signal electrode driver 4 applies a constant current to the organic thin film on the scan electrode selected from the signal electrodes where the pixels to be lit are present. However, the signal electrode driver 4 switches the constant current value according to the controller 2. When the controller 2 instructs normal display, the signal electrode driver 4 passes a first constant current. When the controller 2 instructs the dimming display, the signal electrode driver 4 passes the second constant current. The second constant current amount is smaller than the first constant current amount.

Further, the signal electrode driver 4 displays halftones by adjusting the time for which a constant current is passed through the pixels based on the display data. FIG. 2 is an explanatory diagram showing a situation where the signal electrode driver 4 performs halftone display by PWM. FIG. 2A shows a situation in which halftone display is performed during normal display. The pulse height shown in FIG. 2A represents the potential of the signal electrode when the first constant current is passed. The signal electrode driver 4 continues to flow the first constant current to the pixels displayed at the maximum gradation during the selection period. A first constant current is supplied to a pixel displaying a halftone for a time corresponding to the gradation. Each gradation can be displayed by changing the time during which the first constant current is applied. FIG. 2B shows a situation in which halftone display is performed during dimming display. Since the second constant current amount is smaller than the first constant current amount, the height of the pulse shown in FIG. 2B is lower than the pulse shown in FIG. The signal electrode driver 4 continues to flow the second constant current to the pixels displayed at the maximum gradation during the selection period. A second constant current is supplied to a pixel displaying a halftone for a time corresponding to the gradation. By changing the time during which the second constant current is passed, each gradation can be displayed even during dimming display. Normally, in PWM, immediately after the time for supplying a constant current (time corresponding to a desired halftone) has elapsed, the potential of the signal electrode that has supplied the constant current is set to V _SS (the same potential as the scanning electrode selection potential). Set to.

The scan electrode driver 3 and the signal electrode driver 4 reset the potentials of all the scan electrodes and all the signal electrodes from the end of each scan electrode selection period to the start of the next scan electrode selection period. Set to. Here, it is assumed reset potential is equipotential selection period potential V _SS. Between the time the end of the selection period until the next selection period start, by setting the potentials of all the scanning electrodes and all the signal electrodes in the reset potential V _SS, charges accumulated in pixels are discharged. As a result, at the start of the next selection period, the rise time from the start of the selection period until the pixel emits light is shortened.

  The configurations of the scan electrode driver 3 that sets each scan electrode to the reset potential and the signal electrode driver 4 that sets each signal electrode to the reset potential may be known configurations. For example, the configuration described in Patent Document 1 may be used.

The power supply circuit 5 supplies the voltage V _SS to the scan electrode driver 3, further switches between the voltage V _CH1 and the voltage V _CH2, and supplies the voltage V _CH1 or the voltage V _CH2 . Further, the voltage V _SS and the signal electrode driver power supply voltage V _SH are supplied to the signal electrode driver 4. The voltage V _SH is a voltage for driving a constant current circuit included in the signal electrode driver 4. Therefore, the potential of the signal electrodes is not so set as V _SH.

The power supply circuit 5 outputs the voltage V _CH1 to the scan electrode driver 3 during normal display, and outputs the voltage V _CH2 to the scan electrode driver 3 during dimming display. Scan electrode driver 3 sets the potential of the unselected scan electrode to non-selection potential V _CH1 or V _CH2 in accordance with the voltage output from power supply circuit 5. The power supply circuit 5 switches the output voltages V _CH1 and V _CH2 according to the controller 2.

FIG. 3 is a block diagram illustrating a configuration example of the output unit of the voltages V _CH1 and V _CH2 in the power supply circuit 5. The power supply circuit 5 includes resistors 11 to 13 that divide a power supply voltage, operational amplifiers (hereinafter referred to as operational amplifiers) 14 and 15, and a switch 16. The resistor 11 is connected to the power supply voltage, and the resistor 13 is grounded. The resistor 12 is disposed between the resistor 11 and the resistor 13. The voltage V _CH1in generated between the resistors 11 and 12 by voltage _division is input to the non-inverting input terminal of the operational amplifier 14 connected as a voltage follower. Similarly, the voltage V _CH2in generated between the resistors 12 and 13 by voltage _division is input to the non-inverting input terminal of the operational amplifier 15 connected as a voltage follower. The operational amplifiers 14 and 15 output voltages V _CH1 and V _CH2 , respectively. The voltages V _CH1in and V _CH2in obtained by voltage _division are equal to the voltages V _CH1 and V _CH2 , respectively.

The switch 16 connects the wiring 17 connected to the scan electrode driver 3 to the output terminal of the operational amplifier 14 or the output terminal of the operational amplifier 15 according to a switching control signal output from the controller 2 (not shown in FIG. 3). Let The switching control signal is a control signal for instructing normal display or dimming display. When the switching control signal indicates that the normal display is being performed, the switch 16 connects the wiring 17 to the output terminal of the operational amplifier 14. As a result, the voltage V _CH1 is output from the power supply circuit 5 to the scan electrode driver 3. On the other hand, when the switching control signal indicates that dimming display is being performed, the switch 16 connects the wiring 17 to the output terminal of the operational amplifier 15. As a result, the voltage V _CH2 is output from the power supply circuit 5 to the scan electrode driver 3.

Next, the range of possible values of the non-selection potentials V _CH1 and V _CH2 will be described. First, the range of the potential V _CH2 will be described. Let the emission start voltage be V _p . Further, the signal electrode potential when the second constant current is caused to flow from the signal electrode to the scanning electrode of the selected row by the signal electrode driver 4 is set to V _s2 . FIG. 4 is an explanatory diagram of the lower limit value of _VCH2 . In FIG. 4, the solid line represents the drive waveform of the scan electrode, and the broken line represents the drive waveform of the signal electrode. As shown in FIG. 4A, it is assumed that the non-selection potential _VCH2 is lower than the signal electrode potential _Vs2 . Then, when its potential difference is greater than the light emission starting voltage V _p, so that also the pixels of the row that is not selected will emit light. Therefore, V _CH2 must be a value that satisfies V _s2 −V _CH2 <V _p . That is, V _s2 −V _p <V _CH2 needs to be established. Further, as shown in FIG. 4B, if V _CH2 −V _SS ≦ V _p , the selected row may not emit light even if V _s2 −V _p <V _CH2 is satisfied. obtain. For example, when V _s2 = V _CH2 is established, the pixels in the selected row do not emit light. Therefore, V _CH2 −V _SS > V _p needs to be satisfied. Therefore, it is necessary to satisfy both V _s2 −V _p <V _CH2 and V _SS + V _p <V _CH2 .

Subsequently, the upper limit of V _CH2 will be described. As shown in FIG. 15, when the signal electrode potential approaches the non-selection potential at the start of the selection period, the luminance in the selection period increases from the desired maximum luminance. However, if the amount of increase in luminance within one selection period is within 0.5 times the desired maximum luminance, the linearity when displaying halftones with PWM can be maintained well. Therefore, the upper limit of V _CH2 can be calculated as follows. Let the current value of the second constant current be I ₂ [μA]. The length of the selection period is t [μs (microseconds)]. At this time, the supplied charge in the selection period is I ₂ · t · 10 ⁻³ [nC]. Further, although each pixel has a capacity, the sum of the capacity of the pixels existing in one signal electrode is C [nF]. Since the amount of increase in luminance in one selection period may be within 0.5 times the desired maximum luminance, the supplied charge is I ₂ · t · 0.5 · more than the charge for obtaining the desired luminance. It may be increased by 10 ⁻³ [nC]. Here, since there is a relationship of “charge amount = capacity / voltage”, the signal electrode potential is ((I ₂ · t · 0.5 · 10 ⁻³ ) [nC] / C when V _s2 is used as a reference. [NF]) = (I ₂ · t · 0.5 / C) · 10 ⁻³ [V]. That is, the non-selection potential at which this potential increase can occur is the upper limit of _VCH2 .

In summary, the range that V _CH2 can take is a range that satisfies the following expressions 1 to 3 simultaneously.

V _s2 −V _p <V _CH2 Formula 1

V _SS + V _p <V _CH2 Formula 2

V _CH2 ≦ V _s2 + (I ₂ · t · 0.5 / C) · 10 ⁻³ Formula 3

For example, the non-selection potential V _CH2 may be determined so that V _CH2 = V _s2 and V _SS + V _p <V _CH2 .

The range of the non-selection potential V _CH1 is similarly obtained. That _is, the lower limit of the _{V CH1 is} represented as _{V s1} -V _{p <V CH1.} Here, V _s1 is a signal electrode potential when a first constant current is caused to flow from the signal electrode to the scanning electrode of the selected row by the signal electrode driver 4. Since V _CH2 <V _CH1 , if V _SS + V _p <V _CH2 holds, V _SS + V _p <V _CH1 also holds. Further, the upper limit of V _CH1 is expressed as V _s1 + (I ₁ · t · 0.5 / C) · 10 ⁻³ . However, I ₁ [μA] is the current value of the first constant current. The non-selection potential V _CH1 may be determined so as to be within the above range. In summary, the range that V _CH1 can take is a range that satisfies the following expressions 4 and 5 simultaneously.

V _s1 −V _p <V _CH1 Formula 4

V _CH1 ≦ V _s1 + (I ₁ · t · 0.5 / C) · 10 ⁻³ Formula 5

For example, the non-selection potential V _CH1 may be determined so that V _CH1 = V _s1 .

  FIG. 5 is an explanatory diagram showing the output timing of the control signal output from the controller 2 to the signal electrode driver 4. The controller 2 has a CP (data transfer clock pulse) that defines the timing for sequentially acquiring the data of each column from the display data for one row, and an LP (latch pulse) that indicates the switching of the scan electrode to be selected. The signal is output to the signal electrode driver 4. Further, the controller 2 causes the signal electrode driver 4 to capture display data (Data) for one row. The selection period is from the fall of LP (timing when it is low level) to the rise of LP (timing when it is high). The controller 2 designates a row to be selected from now on, and causes the memory to copy the display data of that row to the data output area. Further, the controller 2 outputs CP to the signal electrode driver 4 as the number of pulse signals equal to the number of signal electrodes during the selection period. The signal electrode driver 4 acquires the data of each pixel one by one from the display data (Data) for one row copied to the data output area at every falling timing of CP. This display data is display data of a row selected in the next selection period.

When the selection period ends, the signal electrode driver 4 determines, based on the display data for one row acquired during the selection period, the signal electrode in which the pixel to be lit during the next selection period exists, It is determined whether to display with gradation. The signal electrode driver 4, LP is while in a high level (i.e., between the time the end of the selection period to the start of the next selection period), and sets the potentials of the signal electrodes to the reset potential V _SS.

When the next selection period is started, the signal electrode driver 4 supplies a constant current to the signal electrode in which the pixel to emit light is present. In each signal electrode, the constant current is stopped when the time corresponding to the gradation has elapsed. The signal electrode driver 4 sets the potential of the signal electrode which has passed a constant current to V _SS.

  As shown in FIG. 1, the controller 2 also outputs a switching control signal (control signal for instructing whether normal display or dimming display) to the signal electrode driver 4. The controller 2 outputs a switching control signal to control switching of a constant current that the signal electrode driver 4 flows. When the normal display is instructed by the switching control signal, the signal electrode driver 4 passes the first constant current as a constant current. On the other hand, when the dimming display is instructed by the switching control signal, the second constant current is passed as the constant current.

FIG. 6 is an explanatory diagram showing the output timing of the control signal output from the controller 2 to the scan electrode driver 3. The controller 2 outputs LP and FLM (first line marker) indicating the start of one frame to the scan electrode driver 3. When the FLM becomes high level, the scan electrode driver 3 sequentially selects each scan electrode from the first row according to LP. The signal electrode driver 4, LP is while in a high level (i.e., between the time the end of the selection period to the start of the next selection period), and sets the potentials of the scanning electrodes to the reset potential V _SS.

  7 and 8 are explanatory diagrams showing examples of drive waveforms when the display panel 1 is driven by the drive device of the present invention. However, FIG. 7 shows an example of a drive waveform when the normal display is maintained and the dimming display is not switched. FIG. 8 shows an example of drive waveforms when switching from normal display to dimming display. 7 and 8 exemplify a case where a constant current is continuously supplied to the pixel to emit light during the selection period.

First, the operations of the controller 2, the scan electrode driver 3, and the signal electrode driver 4 during normal display will be described with reference to FIG. It is assumed that the controller 2 continues to output a signal for instructing normal display (in this example, low level) as a switching control signal. In this case, the power supply circuit 5 outputs the voltage V _CH1 and V _CH1 is set as the non-selection potential.

  When instructing scanning from the first row, the controller 2 changes FLM from low level to high level. Then, while FLM is at high level, LP is raised to high level, and then LP is returned to low level. If LP changes from a low level to a high level while FLM is at a high level, scan electrode driver 3 ends the selection period of the last row at that timing. When LPM changes from high level to low level while FLM is at high level, scan electrode driver 3 starts the selection period of the first row from that timing. The controller 2 changes FLM from high level to low level during the selection period of the first row.

Scan electrode driver 3, when LP is changed from high level to low level while the FLM is at a high level, at that timing, the potential of the first row scan electrode is set to V _SS, each of the other scanning electrodes _Is set to V _CH1 . Further, the signal electrode driver 4 causes a constant current to flow from the signal electrode where the pixel to be lit is present to the first row scan electrode based on the display data acquired in the immediately preceding selection period. At this time, since normal display is instructed, the signal electrode driver passes the first constant current. The signal electrode potential at this time is V _s1 . Further, by setting the potential of each of the other signal electrodes to V _SS, so that no current flows through the first row scan electrode from each of the other signal electrodes. As a result, the organic thin film at the intersection of the signal electrode to which the first constant current is passed and the first row scanning electrode emits light. Since V _CH1 is determined so as to satisfy V _s1 −V _p <V _CH1 , no current flows from the signal electrode to the scan electrode in the non-selected row.

Further, during the selection period of the first row, the signal electrode driver 4 acquires the display data of the second row to be selected next from the memory _2a .

When the controller 2 raises LP to a high level, the selection period of the first row ends. LP is while in the high level, the scan electrode driver 3 and the signal electrode driver 4, the scan electrodes, respectively, to set the potential of the signal electrodes to the reset potential V _SS.

When the controller 2 changes the LP from the high level to the low level, the scan electrode driver 3, at that timing, the potential of the second row scan electrode is set to V _SS, the potential of the other scanning electrodes to V _CH1 Set. Further, the signal electrode driver 4 causes a constant current to flow from the signal electrode where the pixel to be lit is present to the second row scanning electrode based on the display data acquired in the immediately preceding selection period. At this time, since normal display is instructed, the signal electrode driver passes the first constant current. Thereafter, the controller 2, the scan electrode driver 3, and the signal electrode driver 4 repeat the same operation.

FIG. 7 shows an example in which the normal display is maintained. When maintaining the dimming display, the controller 2 continues to output a signal (in this example, high level) that instructs the dimming display as a switching control signal. In this case, the power supply circuit 5 outputs the voltage V _CH2 and V _CH2 is set as the non-selection potential. The signal electrode driver 4 passes a second constant current as a constant current. As a result, the potential of the signal electrode through which the second constant current flows becomes _Vs2 . With respect to points other than the non-selection potential and the potential of the signal electrode through which the second constant current flows, the waveform is the same as the drive waveform shown in FIG.

  Next, the operation when the display is switched will be described with reference to FIG. In the example shown in FIG. 8, the controller 2 switches the switching control signal from a low level (normal display) to a high level (dimming display) in the middle of one frame. The controller 2 switches the switching control signal in accordance with an instruction from the external MPU 6.

  The drive waveform when the switching control signal is at the low level is the same as the drive waveform shown in FIG.

  The controller 2 switches the switching control signal in accordance with, for example, the rise timing of LP (end timing of selection period).

After the rising timing of the LP, LP is while in the high level, the scan electrode driver 3 and the signal electrode driver 4, the scan electrodes, respectively, to set the potential of the signal electrodes to the reset potential V _SS. This is the same as the drive waveform shown in FIG.

After the switching control signal is switched in accordance with the rise timing of LP, when controller 2 changes LP to a low level, the next selection period is started. At this time, the switch 16 of the power supply circuit 5 switches the output voltage according to the change of the switching control signal. Therefore, at the start of the next selection period, the scan electrode driver 3 sets the non-selection potential according to the voltage switched by the switch 16. In the example shown in FIG. 8, the potential of the scan electrode in the non-selected row is set to _VCH2 . The scanning electrode driver 3 sets the potential of the scan electrodes of the selected row to V _SS.

Since the switching control signal is switched so as to instruct dimming display, the signal electrode driver 4 causes the second constant current to flow from the signal electrode where the pixel to be lit is present to the scanning electrode of the selected row. The signal electrode potential at this time is _Vs2 . Further, by setting the potential of each of the other signal electrodes to V _SS, so that no current flows in the scanning electrodes of selected rows from each of the other signal electrodes. As a result, the organic thin film at the intersection of the signal electrode to which the second constant current is passed and the third row scanning electrode emits light. Since V _CH2 is determined so as to satisfy V _s2 −V _p <V _CH2 , no current flows from the signal electrode to the scan electrode in the non-selected row.

  Thereafter, the controller 2, the scan electrode driver 3, and the signal electrode driver 4 operate so as to maintain the dimming display until the switching control signal is switched again.

Although FIG. 8 illustrates the case of switching from normal display to dimming display, the operation when switching from dimming display to normal display is the same. However, in this case, the non-selection potential is switched from V _CH2 to V _CH1 . Further, the constant current flowing from the signal electrode to the scanning electrode of the selected row is switched from the second constant current to the first constant current.

According to this embodiment, when the amount of constant current flowing from the signal electrode to the selected row scanning electrode is reduced when switching to dimming display (switching from the first constant current to the second constant current), the non-selection potential _Is reduced from V _CH1 to V _CH2 . As a result, the potential difference between the signal electrode potential through which the second constant current flows and the non-selection potential is reduced. Therefore, it is possible to prevent the phenomenon that the potential of the signal electrode becomes higher than the potential to be originally set at the start of the selection period, and then drops to the original potential. Therefore, it is possible to maintain good linearity when performing halftone display with PWM.

In _particular, by determining the _{V CH2 ≧ V s2 + (I} 2 · t · 0.5 / C) · 10 -3 to become as _{V CH2,} can be maintained linearity good. Further, by determining V _CH2 so that V _s2 −V _p <V _CH2 , light emission of pixels in the non-selected row can be prevented. Furthermore, by determining V _CH2 so that V _SS + V _p <V _CH2 is also satisfied, the pixels in the selected row can be made to emit light more reliably.

[Embodiment 2] FIG. 9 is a block diagram showing an example of a driving device for an organic EL display device according to a second embodiment of the present invention. Similar to the display panel 1 in the first embodiment, the display panel (organic EL display device) 21 has a plurality of scanning electrodes (not shown) and a plurality of signals arranged so as to be orthogonal to each other with the organic thin film interposed therebetween. An electrode (not shown). However, the display panel 21 in the present embodiment includes a dummy pixel 21 _a. As already explained, if the potential difference between the signal electrode potential when a constant current is passed and the potential at the time of non-selection is large, the signal electrode potential becomes higher than the potential that should be originally set at the start of the selection period. Go down. The dummy pixel _21a is a pixel provided to sample and hold the signal electrode potential that has become the original potential when a constant current is passed after the selection period starts.

Display data of the dummy pixel 21 _a is always constant. Normal Display, the luminance of the dummy pixel 21 _a is constant in each time dimming display, the dummy pixels 21 _a does not contribute to construction of an image to be displayed. Therefore, portions where the dummy pixels 21 _a is present, it is preferable to so as to be covered with the housing or the like so as not to be visible to the viewer. However, the constant current passed from the signal electrode driver 24 to the signal electrode differs between the normal display and the dimming display. During normal display, _a first constant current is passed through the signal electrode where the dummy pixel 21a is present, and during dimming display, _a second constant current is passed through the signal electrode where the dummy pixel 21a is present. Note that, as in the first embodiment, the second constant current amount is smaller than the first constant current amount.

The controller 22 includes a memory 22 _a for storing display data. Then, similarly to the controller 2 in the first embodiment, FLM and LP are output to the scan electrode driver 23, and CP, LP, and Data are output to the signal electrode driver 24, and the scan electrode driver 23 and the signal electrode driver 24 are output. To control. Further, the controller 22 outputs a switching control signal to control switching of a constant current that the signal electrode driver 4 flows. The controller 22 outputs CP and LP to a timing controller 27 described later.

  Note that, when switching between normal display and dimming display, the controller 22 may switch the switching control signal in accordance with, for example, the rise timing of LP (selection period end timing), as in the first embodiment. .

The external MPU 26 instructs the controller 22 as to which of normal display and dimming display is to be executed, like the external MPU 6 described in the first embodiment. The controller 22 switches the switching control signal in accordance with an instruction from the external MPU 26. The external MPU26 performs processing of rewriting the display data stored in the memory 22 _a. However, external MPU26 writes display data including data of the dummy pixels 21 _a in the memory 22 _a. In the following description, the case of writing the data indicating the maximum luminance as a dummy pixel 21 _a data in the memory 22 _a as an example.

The scan electrode driver 23 performs the same operation as that of the scan electrode driver 3 of the first embodiment. That is, to set the potential of the selected scanning electrodes to select at potential V _SS, setting the potential of the scan electrodes of the non-selected row V _{CH1 (normal} display time) or V _{CH2 (dimming} display time). Further, between the time the end of the selection period until the next selection period start (in this embodiment, is. Equipotential selection time potential V _SS) potential reset potential of the scanning electrodes is set to. However, the scan electrode driver 23 is supplied with the voltage V _SS from the power supply circuit 25 and supplied with the voltages V _CH1 and V _CH2 from the operational amplifier 30 described later.

The signal electrode driver 24 performs the same operation as that of the signal electrode driver 4 of the first embodiment. That is, the signal electrode driver 24 supplies a constant current to the organic thin film on the scanning electrode selected from the signal electrode in which the pixel to emit light exists during the selection period. When the normal display is instructed by the switching control signal output from the controller 22, the signal electrode driver 24 passes the first constant current. On the other hand, when the dimming display is instructed by the switching control signal, the second constant current is passed. Further, the signal electrode driver 24 displays halftones by adjusting the time during which the constant current is supplied to the pixels based on the display data. However, in this embodiment, as the display data of the dummy pixels 21 _a, data indicating the maximum brightness is designated by the external MPU 26. Therefore, the signal electrode driver 24, over the entire selection period, continues to flow a current from the signal electrode dummy pixel 21 _a is present. Further, between the time the end of the selection period until the next selection period start, setting the potential of the scan electrodes in the reset potential V _SS.

Power supply circuit 25, as in the first embodiment, supplies the power supply voltage V _SH voltage V _SS and the signal electrode driver to the signal electrode driver 24. In addition, the voltage _VSS is supplied to the scan electrode driver 23. However, the voltages V _CH1 and V _CH2 are not output. Therefore, in this embodiment, the controller 22 does not need to output a switching control signal to the power supply circuit 25.

The timing controller 27 determines a period during which the signal electrode provided with the dummy pixel 21 _a is connected to the capacitor 29 in each of the normal display and the dimming display based on LP and CP output from the controller 22. During that period, a signal SH instructing connection between the signal electrode provided with the dummy pixel 21 _a and the capacitor 29 is output to the switch 28. Further, the period during which the signal electrode provided with the dummy pixel _21a is connected to the capacitor 29 is within the selection period of each scan electrode, and part or all of the period during which the variation in the potential of the signal electrode falls. It is. One electrode of the capacitor 29 is connected to a constant voltage, and the potential is kept constant. In this example, a case where one electrode of the capacitor 29 is grounded and the electrode is maintained at a potential of 0 V will be described as an example.

The switch 28 connects the signal electrode provided with the dummy pixel 21 _a and the electrode 29 _a not grounded of the capacitor 29 while SH is input. As a result, charges are stored in the capacitor 29, the potential of the electrode 29 _a of which is not grounded will signal electrode and the equipotential of the dummy pixels 21 _a is provided. The switch 28 while the SH is not input, and disconnects the connection between the electrode 29 _a of the signal electrode and the capacitor 29.

  A voltage generated between the electrodes of the capacitor due to the accumulation of electric charge in the capacitor 29 is input to the non-inverting input terminal of the operational amplifier 30 connected as a voltage follower. The operational amplifier 30 outputs a voltage equal to the voltage input to the non-inverting input terminal to the scan electrode driver 23. Thus, the capacitor 29 outputs a voltage corresponding to the accumulated charge to the scan electrode driver 23 via the operational amplifier 30. The scan electrode driver 23 sets the non-selection potential according to the voltage output from the operational amplifier 30.

  In the present embodiment, the connection means is realized by the timing controller 27 and the switch 28.

Figure 10 is an explanatory diagram showing a period for connecting the signal electrode dummy pixel 21 _a is provided to the capacitor 29 (the electrode 29 a of which is not _grounded). In FIG. 10, a case where the normal display is switched to the dimming display will be described as an example. When switching from normal display to dimming display, the controller 22 outputs a switching control signal for instructing dimming display to the signal electrode driver 24. Based on the switching control signal, the signal electrode driver 24 causes the second constant current to flow through the signal electrode where the pixel to emit light exists during the selection period. The display data, display data of the dummy pixel 21 _a (data indicating the maximum luminance) are included. Therefore, the signal electrode driver 24 during the selection period, the signal electrode dummy pixel 21 _a is present, continues to flow a second constant current.

At this time, the potential of the signal electrode dummy pixel 21 _a is present should be _(the signal electrode potential when a current of the second constant current to the scanning electrodes of the selected row from the signal electrodes) V _s2. However, in this embodiment, the power supply circuit 25 does not switch the non-selection potential. Therefore, at the selection period start timing immediately after switching from the normal display to the dimming display, the non-selection potential is a high potential during the normal display. Therefore, the difference between the signal electrode potential when the second constant current flows and the non-selection potential is increased, and the potential of the signal electrode becomes higher than V _{s2 as} shown in FIG. 10, and then reaches V _s2. Go down.

The timing controller 27 outputs SH during a period in which the signal electrode potential is lowered to V _s2 (period in which the potential change is suppressed). In the example shown in FIG. 10, the SH output period is from the falling timing of the 64th CP to the falling timing of the 128th CP after the selection period starts (after LP becomes low level). Switch 28, during this period, since the dummy pixel 21 _a is to connect the signal electrode and the electrode 29 _a provided, the potential of the electrode 29 _a becomes _{V s2.}

As a result, the voltage between the electrodes of the capacitor 29 becomes V _s2 , and the voltage V _s2 is input to the operational amplifier 30. The operational amplifier 30 outputs the voltage V _s2 . The scan electrode driver 23 sets the non-selection potential V _CH2 at the time of dimming display by this output voltage.

Thus, when the controller 22 switches the switch control signal, the signal in accordance electrode driver 24 is the switching control signal, the signal electrodes and the dummy pixel 21 _a first to a selected row from existing signal electrode 2 to emit light pixel exists Let the constant current flow. Then, the timing controller 27, switch 28 and capacitor 29 act as a sample and hold circuit, the potential of the signal electrode dummy pixel 21 _a is present at the timing when the electric potential V _s2, inputs the voltage V _s2 to the operational amplifier 30 . The operational amplifier 30 connected as a voltage follower to the capacitor 29 outputs the voltage V _s2 to the scan electrode driver 23. Since the scan electrode driver 23 sets the non-selection potential V _CH2 by the voltage V _s2 , V _CH2 = V _s2 . That is, when the controller 22 switches the switching control signal, the non-selection potential V _CH2 is set to be equal to the signal electrode potential V _s2 when the second constant current flows.

If the non-selection potential V _CH2 and the signal electrode potential V _s2 when the second constant current flow are _equal, the potential of the signal electrode that flows the second constant current at the start of the selection period is higher than V _s2. Is prevented. The signal electrode potential is kept constant while the second constant current is flowing. Therefore, a good linearity can be obtained when displaying a halftone by PWM.

In FIG. 10, the case where the normal display is switched to the dimming display has been described as an example. Next, a case where the dimming display is switched to the normal display will be described. When switching from the dimming display to the normal display, the controller 22 outputs a switching control signal for instructing the normal display to the signal electrode driver 24. Based on the switching control signal, the signal electrode driver 24 supplies a first constant current to the signal electrode in which the pixel to emit light exists during the selection period. The display data, display data of the dummy pixel 21 _a (data indicating the maximum luminance) are included. Therefore, the signal electrode driver 24 during the selection period, the signal electrode dummy pixel 21 _a is present, continues to flow first constant current.

At this time, the potential of the signal electrode in which the dummy pixel _21a is present should be V _s1 (the signal electrode potential when the first constant current is passed from the signal electrode to the scanning electrode of the selected row). However, in this embodiment, the power supply circuit 25 does not switch the non-selection potential. Therefore, at the selection period start timing immediately after switching from the normal display to the dimming display, the non-selection potential is a low potential (V _CH2 ) at the time of dimming display. For this reason, the difference between the signal electrode potential V _s1 when the first constant current flows and the non-selection potential V _CH2 becomes large. At this time, the non-selection potential V _CH2 is lower than the signal electrode potential V _s1 . As a result, at the start of the selection period, the potential of the signal electrode becomes a potential lower than V _s1, rises to then V _s1.

The timing controller 27 outputs SH during a period in which the signal electrode potential is raised to V _s1 (period in which the change in potential is stopped). For example, as in the case shown in FIG. 10, after the start of the selection period (after LP goes low), the output period of SH is from the falling timing of the 64th CP to the falling timing of the 128th CP. And it is sufficient. Since the switch 28 connects the signal electrode provided with the dummy pixel 21 _a and the electrode 29 _a while SH is output, the potential of the electrode 29 _a becomes V _s1 .

As a result, the voltage between the electrodes of the capacitor 29 becomes V _s1 , and the voltage V _s1 is input to the operational amplifier 30. The operational amplifier 30 outputs a voltage V _s1 . The scan electrode driver 23 sets the non-selection potential V _CH1 during normal display by this output voltage.

Thus, when the controller 22 switches the switch control signal, the signal in accordance electrode driver 24 is the switching control signal, first from the signal electrode to a selected row of signal electrodes and the dummy pixels 21 _a pixel to emit light is present is present Let the constant current flow. Then, the timing controller 27, switch 28 and capacitor 29 act as a sample and hold circuit, the potential of the signal electrode dummy pixel 21 _a is present at the timing at which the potential V _s1, inputs the voltage V _s1 to the operational amplifier 30 . The operational amplifier 30 connected as a voltage follower to the capacitor 29 outputs the voltage V _s1 to the scan electrode driver 23. Since the scan electrode driver 23 sets the non-selection potential V _CH1 by the voltage V _s1 , V _CH1 = V _s1 . That is, when the controller 22 switches the switching control signal, the non-selection potential V _CH1 is set to the same potential as the signal electrode potential V _s1 when the first constant current flows.

If the non-selection potential V _CH1 and the signal electrode potential V _s1 when the first constant current flow are _equal, the potential of the signal electrode that flows the first constant current at the start of the selection period is lower than V _s1. Is prevented. Then, the signal electrode potential is kept constant while the first constant current is flowing. Therefore, a good linearity can be obtained when displaying a halftone by PWM.

In the above description, as display data of the dummy pixels 21 _a, shows a case of using the data indicating the maximum luminance. However, the timing controller 27 does not need to continue to output SH until the selection period ends after the change in the signal electrode potential is settled. Thus, the display data of the dummy pixel 21 _a may be any data that the period of change of the potential of the signal electrode is within obtained, it may not necessarily be data that indicates the maximum luminance.

FIG. 9 shows a case where the operational amplifier 30 is connected to the capacitor 29 by a voltage follower so that V _s1 = V _CH1 and V _s2 = V _CH2 . An amplifier may be provided instead of the operational amplifier 30. The voltage V _s1 or V _s2 is input from the capacitor 29 to the amplifier. The amplifier raises or lowers the input voltage and outputs it. The signal electrode driver 23 sets the non-selection potential according to the output voltage of the amplifier. Therefore, the value of the output voltage of the amplifier becomes the value of the potential when not selected.

When the voltage V _s2 is input to the amplifier, the voltage output from the amplifier is _defined as V _CH2 . Possible range of the V _CH2 is the same as the possible range of V _CH2 described in the first embodiment. That is, the range of the voltage V _CH2 that can be output by the amplifier when the voltage V _s2 is input is a range that simultaneously satisfies the conditions of Expressions 1 to 3. When the voltage V _s1 is input to the amplifier, the voltage output from the amplifier is V _CH1 . Possible range of the V _CH1 is similar to the possible range of V _CH1 described in the first embodiment. That is, the range of the voltage V _CH1 that can be output by the amplifier when the voltage V _s1 is input is a range that satisfies the expressions 4 and 5 simultaneously.

Here, the output voltage _{V CH2} amplifier (unselected potential _{V CH2} at dimming) is, how high with respect to the input voltage of the amplifier _{V s2} (potential _{V s2} of the signal dummy pixels 21 _a are provided electrodes) A specific example is given as to whether a value is allowed.

Assume that the number of scan electrodes and signal electrodes provided in the display panel 1 is 64 and 256, respectively, and the number of pixels is 256 × 64 pixels. Further, it is assumed that the vertical and horizontal widths of each pixel are each 0.3 [mm]. Further, it is assumed that the size of the capacitance of the pixel per unit area is 0.25 [nF / mm ² ]. In addition, the frame frequency when driving the display panel 1 is 100 Hz, and the duty ratio (the ratio of the time during which one scan electrode is selected with respect to one frame) is 1/64. Further, it is assumed that the luminous efficiency is 3 [cd / A] and the maximum luminance required during dimming display is 5 [cd / m ² ]. If the amount of increase in luminance in one selection period is within 0.5 times the maximum luminance (here, 5 [cd / m ² ]), the linearity when displaying a halftone with PWM can be maintained well. .

In this case, the capacity of one pixel is 0.25 [nF / mm ² ] × 0.3 [mm] × 0.3 [mm] = 22.5 [pF]. Since there are 64 pixels in one signal electrode, the capacity of one signal electrode is 22.5 [pF] × 64 = 1440 [pF] = 1.44 [nF].

The current value of the second constant current is (5 [cd / m ² ] × 64 × 0.3 [mm] × 0.3 [mm]) / 3 [cd / A] = 9.6 [μA ]. One selection period is (1 [s] / 100 [Hz]) × (1/64) = 156 [μs].

The electric charge supplied in one selection period is calculated | required by the product of an electric current and time (selection period). Therefore, the charge supplied in one selection period is 9.6 [μA] × 156 [μs] = 1.498 [nC]. Since the amount of increase in luminance in one selection period only needs to be within 0.5 times the maximum luminance, the supplied charge is 0.5 times the charge 1.498 [nC] for obtaining the desired luminance. Only as much may be supplied. The amount of charge that may be supplied more than the charge for obtaining the desired luminance is 1.498 [nC] × 0.5 = 0.649 [nC]. Further, there is a relationship “charge amount = capacity / voltage”. Therefore, when a larger amount of charge is supplied, the signal electrode potential rises by 0.749 [nC] /1.44 [nF] = 520 [mV] = 0.5 [V]. That is, the increase in signal electrode potential is allowed to 0.5 [V]. Therefore, in this example, the non-selection potential V _CH2 at the time of dimming is allowed to a value higher by 0.5 [V] than the potential V _{s2 of the} signal electrode provided with the dummy pixel 21 _a .

In the second embodiment, the dummy pixels 21 _a provided, when the potential change of the signal electrodes dummy pixels 21 _a are provided has subsided, the signal electrode and the capacitor 29 (electrode of which is not grounded 29 _a ) is connected. Without providing dummy pixels 21 _a, when the potential change of the signal electrode pixels constituting an image to be displayed on the viewer there has subsided, it may be configured to be connected and its signal electrode and the capacitor 29. However, in this case, the signal electrode connected to the capacitor 29 varies depending on the display data. Therefore, the controller 22 notifies the switch 28 which signal electrode and capacitor 29 should be connected. The switch 28 may connect the signal electrode notified from the controller 22 to the capacitor 29 while SH is input. The controller 22 selects a pixel in which a period during which the signal electrode potential falls is present (for example, a pixel in which a current continues to flow from the falling timing of the 64th CP to the falling timing of the 128th CP after the selection period starts). Determine based on display data. Then, the switch 28 is notified of the signal electrode in which the pixel exists.

The signal electrode connected to the capacitor 29 (the non-grounded electrode 29 _a ) when the potential change of the signal electrode through which the first constant current or the second constant current flows is at least 1 I need a book. Therefore, when providing the dummy pixel 21 _a, a signal electrode dummy pixel 21 _a is present may be at least one. When the dummy pixel _21a is not provided, the controller 22 may notify the switch 28 that it is connected to the capacitor 29 of at least one signal electrode.

[Third Embodiment] FIG. 11 is a block diagram showing an example of a driving device for an organic EL display device according to a third embodiment of the present invention. The configuration of the display panel (organic EL display device) 41 is the same as that of the display panel 1 in the first embodiment.

The controller 42 includes a memory 42 _a for storing display data. Then, similarly to the controller 2 in the first embodiment, FLM and LP are output to the scan electrode driver 43, and CP, LP, and Data are output to the signal electrode driver 44, and the scan electrode driver 43 and the signal electrode driver 44 are output. To control. In addition, the controller 42 outputs a switching control signal to control switching of a constant current that the signal electrode driver 44 flows. Note that, when switching between normal display and dimming display, the controller 42 may switch the switching control signal in accordance with, for example, the rise timing of LP (the end timing of the selection period), as in the first embodiment. .

The external MPU 46 instructs the controller 42 as to which of normal display and dimming display is to be executed, as with the external MPU 6 described in the first embodiment. The controller 42 switches the switching control signal in accordance with an instruction from the external MPU 46. The external MPU46 performs processing of rewriting the display data stored in the memory 42 _a.

The scan electrode driver 43 performs the same operation as that of the scan electrode driver 3 of the first embodiment. That is, to set the potential of the selected scanning electrodes to select at potential V _SS, setting the potential of the scan electrodes of the non-selected row V _{CH1 (normal} display time) or V _{CH2 (dimming} display time). Further, between the time the end of the selection period until the next selection period start (in this embodiment, is. Equipotential selection time potential V _SS) potential reset potential of the scanning electrodes is set to. However, the scan electrode driver 43 is supplied with the voltage V _SS from the power supply circuit 45 and supplied with the voltages V _CH1 and V _CH2 from the signal electrode driver 44.

The signal electrode driver 44 performs the same operation as that of the signal electrode driver 4 of the first embodiment. That is, the signal electrode driver 44 applies a constant current to the organic thin film on the scanning electrode selected from the signal electrode in which the pixel to emit light exists during the selection period. When the normal display is instructed by the switching control signal output from the controller 42, the signal electrode driver 44 passes the first constant current. On the other hand, when the dimming display is instructed by the switching control signal, the second constant current is passed. Note that, as in the first embodiment, the second constant current amount is smaller than the first constant current amount. Further, the signal electrode driver 44 displays a halftone by adjusting the time for which a constant current is supplied to the pixel based on the display data. Further, between the time the end of the selection period until the next selection period start, setting the potential of the scan electrodes in the reset potential V _SS.

However, in the present embodiment, the signal electrode driver 44 is a voltage that changes linearly according to a constant current output to the signal electrode (that is, a voltage expressed as a linear function with the current value of the constant current as a variable). Is output to the scan electrode driver 43. Since a relatively small constant current (second constant current) is output during dimming display, the signal electrode driver 44 outputs a voltage V _CH2 corresponding to the second constant current to the scan electrode driver 43. In addition, since the first constant current larger than the second constant current is output during normal display, the signal electrode driver 44 outputs the voltage V _CH1 corresponding to the first constant current to the scan electrode driver 43.

Power supply circuit 45, as in the first embodiment, the signal electrode driver 44 supplies a voltage _{V SS,} and a power supply voltage _{V SH} signal electrode driver. In addition, the voltage _VSS is supplied to the scan electrode driver 43. However, the voltages V _CH1 and V _CH2 are not output. Therefore, in this embodiment, the controller 42 does not need to output a switching control signal to the power supply circuit 45.

  FIG. 12 is an explanatory diagram showing a configuration example of the signal electrode driver 44 that outputs a voltage that linearly changes according to a constant current. As shown in FIG. 12, the signal electrode driver 44 includes a DA conversion circuit 61. The DA conversion circuit 61 performs DA conversion on the switching control signal output from the controller 42. The DA conversion circuit 61 is connected to the + terminal of the first operational amplifier 62. The output of the first operational amplifier 62 is connected to the base of the first transistor 63. The emitter of the first transistor 63 is connected to the negative terminal of the first operational amplifier 62 and the first resistor 64. The other end of the first resistor 64 (the opposite side of the first transistor 63) is kept at a constant potential. In this example, the case where the other end of the first resistor 64 is grounded and maintained at a potential of 0 V is shown as an example. Note that the first resistor 64 is often provided outside the signal electrode driver 44.

A second resistor 65 and a plurality of third resistors 66 are connected in parallel to the wiring 60 to which the signal electrode driver power supply voltage V _SH is input. The other end (opposite side of the wiring 60) of each third resistor 66 is input to the emitter of the second transistor 67. Each third resistor 66 and each second transistor 67 correspond one to one. The resistance values of the third resistors 66 are all equal. The other end of the second resistor 65 (the opposite side of the wiring 60) is connected to the collector of the first transistor and the base of each second transistor.

  Except for one second transistor, the collector of each second transistor causes a constant current to flow from the output terminal of the signal electrode driver 44 to the signal electrode.

The collector of the second transistor 66 not connected to the signal electrode is connected to the fourth resistor 68. The fourth resistor 68 is connected in series with the fifth resistor 69. The other end of the fifth resistor (the opposite side of the fourth resistor 68) is connected to a grounded constant voltage power supply 70. In addition, a second operational amplifier 71 connected as a voltage follower is connected to a connection portion between the fourth resistor 68 and the fifth resistor 69. The voltage value V _L of the constant voltage power supply 70 is approximately the same as the light emission start voltage.

  A constant current equal to the constant current flowing through the signal electrode also flows from the second transistor 67 to the fourth resistor 68. The second operational amplifier 71 receives the voltage at the connection between the fourth resistor 68 and the fifth resistor 69 and outputs a voltage equal to the voltage. The voltage value output from the second operational amplifier 71 changes linearly with respect to the constant current value flowing through the fourth resistor 68. The voltage output from the second operational amplifier 71 is supplied to the scan electrode driver 43. The scan electrode driver 43 sets a non-selection potential with this voltage. Accordingly, the voltage value output from the second operational amplifier 71 is equal to the value of the non-selection potential.

In the configuration shown in FIG. 12, the constant current value I _ref flowing through the first transistor is determined by the output of the DA converter circuit 61 and the resistance value of the first resistor 64. Then, the potential at the other end a of the second resistor 65 (on the opposite side of the wiring 60) is determined by the second resistor 65 and the current value _Iref . Furthermore, the current value of the constant current output from the signal electrode driver 44 to the signal electrode is determined by the potential at the other end a of the second resistor 65 and the resistance value of the third resistor 66.

  The switching control signal input to the DA conversion circuit 61 differs between the normal display and the dimming display. Accordingly, the output of the DA conversion circuit 61 is also different. As a result, the current value of the constant current output to the signal electrode is different between the normal display and the dimming display, and the first constant current is output during the normal display, and the second constant current is output during the dimming display. .

The voltage output from the second operational amplifier 71 when the second constant current flows through the fourth resistor 68 is _{defined as VCH2} . Possible range of the V _CH2 is the same as the possible range of V _CH2 described in the first embodiment. That is, the range that V _CH2 can take is that when the current value of the second constant current is I ₂ and the potential of the signal electrode when the second constant current flows is V _s2 , Equations 1 to 3 can be simultaneously applied. This is a satisfactory range.

A voltage output from the second operational amplifier 71 when the first constant current flows through the fourth resistor 68 is _defined as V _CH1 . Possible range of the V _CH1 is similar to the possible range of V _CH1 described in the first embodiment. That is, the range that V _CH1 can take is that when the current value of the first constant current is I ₁ and the potential of the signal electrode when the first constant current flows is V _s1 , Equations 4 and 5 are simultaneously used. This is a satisfactory range.

The resistance value of the fourth resistor 68, the resistance value of the fifth resistor 69, and the voltage value V _L of the constant voltage power source 70 are within the range where the voltage V _CH2 satisfies Equations 1 to 3 simultaneously, and the voltage V _CH1 is What is necessary is just to define so that it may be settled in the range which satisfies Formula 4 and Formula 5 simultaneously.

  In the present embodiment, the voltage output means is realized by the fourth resistor 68, the fifth resistor 69, the constant voltage power supply 70, and the operational amplifier 71.

The solid line shown in FIG. 13 indicates the relationship between the current that flows from the signal electrode to the scan electrode in the selected row (equal to the current that flows through the fourth resistor 68) and the output voltage of the second operational amplifier 71. As shown in FIG. 13, the output voltage of the second operational amplifier 71 changes linearly with respect to the current value. In other words, the output voltage of the second operational amplifier 71 is expressed as a linear function of the current value of the constant current flowing through the signal electrode. When the second constant current (current value I ₂ ) flows, the output voltage of the second operational amplifier 71 becomes V _CH2 . Further, when the first constant current (current value I ₁ ) is supplied, the output voltage of the second operational amplifier 71 becomes V _CH1 .

Further, a curve represented by a broken line in FIG. 13 indicates a relationship between a current flowing from the signal electrode to the scanning electrode of the selected row and a potential of the signal electrode. As shown in FIG. 13, when the second constant current (current value I ₂ ) is passed from the signal electrode to the scan electrode, the potential of the signal electrode becomes V _s2 . Further, when the first constant current (current value I ₁ ) is passed from the signal electrode to the scan electrode, the potential of the signal electrode becomes V _s1 .

When no current is passed from the signal electrode to the scan electrode (when the current value is 0 [A]), the output voltage of the second operational amplifier 71 is _VL .

When the second constant current is passed during dimming display, the potential difference between the signal electrode potential _Vs2 and the non-selection potential _VCH2 is relatively small as shown in FIG. Therefore, the potential of the signal electrode that allows the second constant current to flow at the start of the selection period is prevented from becoming higher than _Vs2 . Then, the signal electrode potential is kept substantially constant while the second constant current is flowing. Therefore, a good linearity can be obtained when displaying a halftone by PWM.

Similarly, when the first constant current is passed during normal display, the potential difference between the signal electrode potential _Vs1 and the non-selection potential _VCH1 is relatively small as shown in FIG. Therefore, the potential of the signal electrode that allows the first constant current to flow at the start of the selection period is prevented from becoming higher than V _s1 . The signal electrode potential is kept substantially constant while the first constant current is flowing. Therefore, a good linearity can be obtained when displaying a halftone by PWM.

Note that, when a current having an intermediate value between the current values I ₁ and I ₂ is passed, the difference between the signal electrode potential and the non-selection potential (the output voltage of the second operational amplifier 71) increases. However, since such a current is not passed during normal display and dimming display, there is no possibility that good linearity cannot be obtained.

  In each of the above embodiments, the case where each signal electrode potential and each scan electrode potential are set to the reset potential from the end of the selection period to the start of the next selection period has been described as an example. As in the driving method described in Patent Document 2, the potential of the scan electrode that has been selected until then is set to the non-selection potential from the end of the selection period to the start of the next selection period. The potential of each scan electrode may be set to the reset potential. Alternatively, from the end of the selection period to the start of the next selection period, the potential of the next scan electrode to be selected may be set to the non-selection potential, and the potential of each of the other scan electrodes may be set to the reset potential. . Alternatively, from the end of the selection period to the start of the next selection period, the potential of the scan electrode that has been selected up to that point and the potential of the next scan electrode to be selected are set to non-selection potentials, and each of the other scan electrodes May be set to the reset potential.

  INDUSTRIAL APPLICABILITY The present invention is applicable to an organic EL display device, and in particular, performs high-brightness image display and low-brightness image display, respectively, and also displays high-brightness image display and low-brightness image display. Application to an organic EL display device that displays a halftone in each case is useful. For example, application to a display device or the like of an in-vehicle navigation system that displays an image with high luminance when the surroundings are bright and displays an image with low luminance when the surroundings are dark is useful.

The block diagram which shows the example of the drive device of the organic electroluminescent display apparatus of the 1st Embodiment of this invention. Explanatory drawing which shows the condition where a signal electrode driver performs halftone display by PWM. The block diagram which shows the structural example of the output part of voltage _VCH1 and _VCH2 in a power supply circuit. Explanatory drawing of the lower limit of _VCH2 . Explanatory drawing which shows the output timing of the control signal which a controller outputs to a signal electrode driver. Explanatory drawing which shows the output timing of the control signal which a controller outputs to a scanning electrode driver. Explanatory drawing which shows the example of the drive waveform at the time of driving a display panel with the drive device of this invention. Explanatory drawing which shows the example of the drive waveform at the time of driving a display panel with the drive device of this invention. The block diagram which shows the example of the drive device of the organic EL display apparatus of the 2nd Embodiment of this invention. Explanatory drawing which shows the period which connects the signal electrode in which a dummy pixel is provided to a capacitor | condenser. The block diagram which shows the example of the drive device of the organic electroluminescent display apparatus of the 3rd Embodiment of this invention. Explanatory drawing which shows the structural example of the signal electrode driver in 3rd Embodiment. Explanatory drawing which shows the relationship between the electric current sent from the signal electrode to the scanning electrode of the selected row, and the output voltage of a 2nd operational amplifier. Explanatory drawing which shows the example of the drive waveform in the conventional drive method. Explanatory drawing which shows the example of a drive waveform at the time of switching to a dimming display by reducing a constant current value in the conventional drive method.

Explanation of symbols

1 Organic EL display device (display panel)
2 Controller 2 _a Memory 3 Scan electrode driver 4 Signal electrode driver 5 Power supply circuit 6 External MPU

Claims (5)

A driving device for an organic EL display device in which an organic thin film is disposed between a plurality of scanning electrodes and a plurality of signal electrodes,
A scan electrode driver that scans scan electrodes while selecting individual scan electrodes;
A signal electrode driver for supplying a constant current to the organic thin film on the scanning electrode selected from the signal electrode in which the pixel to be lit is present;
The signal electrode driver passes a first constant current or a second constant current having a current value lower than the first constant current,
When the signal electrode driver passes the first constant current, the scan electrode driver sets the selected scan electrode to the selected potential, sets the unselected scan electrode to the first non-selected potential, When the driver passes the second constant current, the selected scan electrode is set to the selected potential, and the unselected scan electrode is set to the second unselected potential that is lower than the first unselected potential. A drive device for an organic EL display device. A power supply circuit that outputs a voltage for setting the scan electrode to the first non-selection potential and a voltage for setting the scan electrode to the second non-selection potential to the scan electrode driver;
Control means for controlling switching of a constant current supplied by the signal electrode driver and switching of a voltage output from the power supply circuit to the scan electrode driver,
When the first constant current is allowed to flow through the signal electrode driver, the control means causes the power supply circuit to output a voltage for setting the scan electrode to the first non-selection potential, and causes the signal electrode driver to output the second constant current. , The voltage for setting the scan electrode to the second non-selection potential is output to the power supply circuit,
2. The organic EL according to claim 1, wherein the scan electrode driver sets the potential of the unselected scan electrode to the first non-selection potential or the second non-selection potential according to the voltage output from the power supply circuit. Drive device for display device. A capacitor with one electrode connected to a constant voltage;
Within the selection period of each scan electrode, when the potential change of the signal electrode through which the first constant current or the second constant current flows is settled, at least one of the signal electrodes and the capacitor A connecting means for connecting the other electrode and storing in the capacitor a charge corresponding to the potential of the signal electrode connected to the other electrode;
The capacitor outputs a voltage corresponding to the accumulated charge to the scan electrode driver,
2. The organic EL according to claim 1, wherein the scan electrode driver sets the potential of the scan electrode that is not selected to the first non-selection potential or the second non-selection potential according to the voltage output from the capacitor. Drive device for display device. The signal electrode driver includes voltage output means for outputting a voltage that changes linearly according to a current value of a constant current flowing through the signal electrode,
2. The organic device according to claim 1, wherein the scan electrode driver sets the potential of the unselected scan electrode to the first non-selection potential or the second non-selection potential according to the voltage output from the voltage output means. Drive device for EL display device. The light emission start voltage of the organic thin film is V _p [V], the current value of the second constant current is I ₂ [μA], and the potential of the signal electrode when the second constant current is passed by the signal electrode driver is V _s2 [V], the length of the selection period is t [μs], the sum of the capacitances of the pixels existing in one signal electrode is C [nF], and the selection potential is V _SS [V]. When the second non-selection potential is V _CH2 [V], the second non-selection potential V _CH2 is
V _s2 −V _p <V _CH2 ,
V _SS + V _p <V _CH2 and V _CH2 ≦ V _s2 + (I ₂ · t · 0.5 / C) · 10 ⁻³
The drive device for an organic EL display device according to any one of claims 1 to 4, wherein:

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