JPH0718987B2 - Display device - Google Patents

Description

The present invention relates to a matrix type display device using a liquid crystal held between a substrate having a plurality of row electrodes and a counter substrate having a plurality of column electrodes.

In the conventional matrix type display device, as the number of row electrodes increases, the drive duty ratio decreases and the operation margin decreases.
Further, there is a problem that a cross effect occurs because each pixel is not independent, and as a means for solving this, it was considered to insert a diode in series with the liquid crystal in each pixel to separate them. FIG. 1 is a block diagram of one pixel of a display device proposed in the past. (1) is a row electrode (2) is a column electrode,
(3) is a diode, (5) is a liquid crystal of one pixel,
(3) is located between the display electrodes (4) of (1) and (5). (1) and (2) are formed on two substrates facing each other, and (3) is integrated on the substrate on which (1) is formed. However, this conventional display device has a problem in display quality because it is difficult to drive the liquid crystal in an alternating current.

An object of the present invention is to eliminate the above drawbacks in a matrix type display device, and to provide a high density information display device.

In the matrix type display device of FIG. 1, two diodes are arranged between the display electrode and the row electrode so as to be bidirectional, and if a drive signal is devised, an inversion potential is applied between the drive electrodes of the liquid crystal and AC drive is performed. be able to.

According to the present invention based on this idea, liquid crystal is sandwiched between a substrate having a plurality of row electrodes and a counter electrode substrate having a plurality of column electrodes, the row electrodes and the column electrodes are arranged in a matrix, and two rows are provided. A pair of electrodes is provided, pixels are provided corresponding to the intersections with the column electrodes, and a forward direction is provided between the first row electrode (1) and the second row electrode (6) which are a pair of row electrodes. Two diodes serially connected to each other are provided, the anode of the first diode (3) is connected to the first row electrode (1), and the cathode of the second diode (7) is the second row electrode. The display electrode (4), which is one of the electrodes of the liquid crystal (5), is connected to the connection point of the cathode of the first diode (3) and the anode of the second diode (7). The other electrode of the liquid crystal (5) is connected to the electrode (2) and is a table showing the signal potential of the display electrode (4) of the liquid crystal (5). Voltage liquid crystal voltages between the pixel signal potential of the column electrodes applied to the other electrode of the electrode potential Vd and the liquid crystal (5) V _LC (liquid crystal voltages V _LC = applied to the display electrode potential Vd- other electrode A pixel device having a pixel electrode potential of a column electrode) and performing AC driving, and one frame period including a pixel selection period in which a row electrode is selected and a non-selection period in which another row electrode is selected. Is formed, AC driving is performed by applying an inversion potential between the display electrode (4) of the liquid crystal (5) and the other electrode in two frame periods, and a pixel selection period in the pixel of row k and column l in the in the first signal potential V _r ^k ₁ row electrodes and the signal potential V _r ^k ₂ of the second row electrode is made to almost the same potential, pixel selection period S1 of one frame period two potential V _r ^k ₁ of the present row electrodes, V _r ^k ₂ is the first selection potential V1, this time First display electrode potential Vd _S1 is defined, the potential V _r ^k ₁ of the two row electrodes in the pixel selection period S2 of the other frame period, V _r ^k ₂ is the second selection potential V2, the Sometimes, the second display electrode potential Vd _S2 is determined (second selection potential V2> first selection potential V1), and the pixel signal potential V _c ^l of the column electrode is changed according to the pixel. pixel signal potential second selection potential V2 ≧ column electrodes V _c ^l ≧ first selection potential V1, is the desired voltage value that satisfies the relationship, the pixel signal voltage V _c ^l of column electrodes in a pixel selection period S1 1 of the pixel signal voltage V _c ^l _-S1, pixel selection period S1, the pixel signal voltage V _c ^l of column electrodes in a pixel selection period S2 is the second pixel signal voltage V _c ^l _-S2 to the row electrodes are selected, in S2, the first display electrode potential Vd _S1 - the first pixel signal voltage V _c ^l _-S1 =
-1 ((second display electrode potential Vd _S2 -second pixel signal potential
V _c ^l _-S2 ), and in the non-selection periods H1 and H2 following the pixel selection periods S1 and S2, respectively, l
The pixel signal potential V _c ^l of the column electrode of the column is changed according to the pixel selection period of the row electrodes other than the k row, and at this time, k
The potential applied to the two row electrodes of the row is the signal potential V _r ^k _{2 of the second} row electrode> the pixel signal potential V _{c of the} column electrode.
^l + the liquid crystal voltage V _LC applied in the selection period> the signal potential V _r ^k ₁ of the first row electrode is satisfied, and the non-selection period H1 in one frame period is satisfied.
In the liquid crystal voltage V _LC which is held in the non-selection period of the liquid crystal voltages V _LC and the other frame period is held H2 absolute value thereof substantially equal polarity is summarized in that comprising inverted.

FIG. 2 is a block diagram of one pixel in the display device of the present invention. FIG. 2 is different from FIG. 1 in that the row electrode is composed of two row electrodes that make a pair, that is, a first row electrode (1) and a second row electrode (6), and a display electrode (4). A first diode (3) and a second diode (7) which are opposite to each other are formed between the first row electrode (1), the first diode (3) and the display electrode (4). ), The second row electrode (6),
It differs from FIG. 1 in that the second diode (7) is formed on the same substrate. The same potential is applied to the first row electrode (1) and the second row electrode (6) during the selection period of the pixels in this row, and the potential of the display electrode (4) is set to that potential,
A voltage between the pixel signal potential applied to the column electrode (2) formed on the counter substrate and the potential of the display electrode (4) is applied to the liquid crystal in the pixel. This is the liquid crystal voltage V _LC .

Further, in the non-selection period, the first diode (3) and the second diode (7) are reversed to the first row electrode (1) and the second row electrode (6) with respect to the display electrode (4). A display is performed by applying a potential biased in the direction, holding the voltage between the drive electrodes of the liquid crystal applied during the pixel selection period in which the pixel is selected, controlling the alignment of the liquid crystal molecules, and applying optical modulation. Here, the same potential applied to the two electrodes forming a pair of row electrodes during the pixel selection period can be set to a potential in the vicinity, typically within a range of 100 mV.

Various potentials are applied to the column electrodes during the non-selection period, but a capacitor is inserted between the display electrodes and the column electrodes so as to eliminate the voltage attenuation during this period and obtain a sufficient contrast. (8)
Is the capacity, that is, the display voltage storage capacity between the drive electrodes of the liquid crystal. The display voltage storage capacity (8) is equal to the first row electrode (1),
It is integrated on the same substrate as the second row electrode (6). Therefore, the substrate having a plurality of row electrodes has a plurality of column electrodes individually connected to the column electrodes of the counter substrate, and the capacitor is formed between the column electrodes and the display electrodes. Therefore, in FIG. 2, the column electrode (2) formed on the counter substrate is connected to the opposing substrate at the end of the substrate, and the connected column electrode has the electrode on one side of the display voltage storage capacitor (8). Connected.

FIG. 3 is a drive waveform diagram of the embodiment of the display device of the present invention, and shows the waveform in the pixel at the k-th row and the l-th column.
V _r ^k ₁ , V _r ^k ₂ , V _c ^l , Vd, and V _LC are (1) and (1) in FIG. 2, respectively.
Signal potentials or voltages corresponding to the drive electrodes of (6), (2), (4), and (5), which are the signal potential V _r ^k ₁ of the first row electrode and the signal of the second row electrode. potential V _r ^k ₂ ,, column pixel signal voltage V _c ^l of electrodes, the display electrode potential Vd, a liquid crystal voltage V _LC.

Signal potential V _r ^k ₁ of the first row electrode, signal potential of the second row electrode
V _r ^k ₂ has the same potential in the pixel selection periods S1 and S2 (the potential in the pixel selection period S1 is the first selection potential V1 and the potential in the pixel selection period S2 is the second selection potential V2) , Non-selection period H1, H2
Therefore, the two diodes are biased in the opposite direction with respect to the display electrode potential Vd. V _c ^l is a pixel signal potential O～V, signal potential V _r ^k ₁ of the first row electrode in the pixel selection period S1, the signal potential V _r ^k ₂ That display electrode potential of the second row electrode
Since Vd is 0, the liquid crystal voltage V _LC
Becomes (0-V _c ^l ). Since the non-selected interval H1 in two diodes are biased in the reverse direction in terms of the display electrodes of FIG. 2 (4) becomes a high impedance state, the display electrode potential Ji order signal change of the pixel signal voltage V _c ^l since Vd is changed, the liquid crystal voltage V _LC = Vd-V _c ^l is kept substantially uniform within this period. That is, the voltage value between the driving electrode plates of the liquid crystal is almost maintained.

In the pixel selection period S2, the signal potential V _r ^k ₁ of the _first row electrode, the second row electrode
Since the signal potential V _r ^k ₂ That display electrode potential Vd of the row electrodes is V, the pixel signal voltage V _c ^l is the (V- pixel signal voltage V _c ^l _-S1 when the pixel selection period S1), liquid crystal voltages V _LC is {pixel signal voltage V _c ^l _-S1 × when the pixel selection period S1 (-1)}. The non-selection period H2 is the same as the non-selection period H1 in the pixel selection period.
Holds the liquid crystal voltage V _LC at S2. Display electrode potential Vd is −
It changes with the potential of V to 2V.

Thus the signal potential V _r ^k ₁ of the first row electrodes, -V-alpha to the signal potential V _r ^k ₂ of the second row electrodes reverse bias the two diodes in the non-selection period is achieved, It has a potential of. The reverse bias of the two diodes should be the same for pixels in any column of row k. Then, the pixel selection period S1 / non-selection period H1 (first frame period) and the subsequent pixel selection period S2 /
Non-selection period H2 period (adjacent second frame period)
Then, the pixel signal potential V _c ^l is a potential inverted around V / 2,
The liquid crystal voltage V _LC is a voltage whose sign is inverted, and AC driving of the liquid crystal is achieved.

The voltage value of the display electrode (4) in the pixel selection period S1 is Vd _S1 , and that in the pixel selection period S2 is Vd _S2 .

FIG. 4 is a drive waveform diagram of a reference example related to the present invention,
The waveforms at the pixels in the k-th row and the l-th column are shown.
Defining _{^{V r k 1, V r k}} 2, V c l, Vd, V LC, S1, S2, H1, H2 is the same as the embodiment of FIG. 3,. The difference from Fig. 3 is the pixel selection period
S1, S2 at the signal potential V _r ^k ₁ of the first row electrodes, the signal potential V _r ^k ₂ potential is equal 0 for the second row electrode, the pixel signal voltage V _c ^l is -V
That is, the potential is ~ V. Pixel selection period S1
In period and the pixel selection period S2 · non-selection period periods of H2 in a non-selection period H1, the pixel signal voltage V _c ^l, the liquid crystal voltage V _LC is inverted voltage reference numerals, has a potential, the display electrode potential Vd - 2V ~ 2V
The signal potential V _r ^k ₁ of the first row electrode and the signal potential V _r ^k ₂ of the second row electrode are − in order to achieve the reverse bias of the two diodes during the non-selection period. 2V-α, It has a potential of.

In the embodiment of FIG. 3, the pixel signal potentials applied to the column electrodes are pixel selection period S1, non-selection period H1 and pixel selection period S2.
-It is possible to display gradation by changing the voltage by setting the potential to be a binary value or more that is inverted in the non-selection period H2, while the voltage applied to the liquid crystal display electrode (4) is Vd depending on the pixel selection period.
_S1 ≠ Vd _S2 .

Further, color display can be realized by further disposing a color filter on the counter substrate. In addition, the period during which the pixels are lit in the plurality of frame periods is individually changed by the pixel signal to change the effective liquid crystal drive voltage value for gradation display, and the entire area of the display device or a selected area is displayed. By selecting the same for all pixels, it is possible to display by changing the duty ratio.

The diode in the present invention is formed by a PIN junction diode made of polycrystalline silicon or amorphous silicon, and an insulating substrate such as glass or ceramics is used as the substrate. In particular, amorphous silicon diodes produced by plasma CVD have many advantages because they can be continuously formed in a laminated structure by changing the dopant such as B ₂ H ₆ and PH ₃ at a relatively low temperature.

The display system can be applied to both a reflective type and a transmissive type, and the diode is shielded by a metal electrode so as to eliminate the influence of light, but this is also used by the electrode of the diode.

In FIG. 3 (shown as a reference example in FIG. 3), the two electrodes of the row electrodes that are changing at the same time do not change at the same time when the same potential is applied, but at the same time. The order of this change may be changed between the pixel selection period S1 and the pixel selection period S2.

The capacitance parasitic on the diode becomes equal under the same bias condition if the first diode (3) and the second diode (7) in FIG. 2 are selected to have the same shape. Throughout the pixel selection period S1, the non-selection period H1, the pixel selection period S2, and the non-selection period H2, the electric potentials _Vr ^k ₁ and V _r ^k ₂ of the two electrodes of the row electrode as a whole
Is selected so as to change in the same amount in the opposite direction as shown in FIG. 3 (FIG. 4 is a reference example), so that the DC component of the potential change of the display electrode due to the parasitic capacitance can be canceled. The storage capacity of the display voltage inserted in parallel with the liquid crystal in the pixel can be selected to be large enough for the parasitic capacitance of the diode and the capacitance sum of the liquid crystal, and a stable liquid crystal drive voltage can be applied throughout the pixel selection period and non-selection period. To be Also, the one-side electrode to which the capacitor is connected can be connected to a column-shaped electrode that changes the potential in the vicinity but is equal in synchronization with the potential change of the corresponding column electrode of the counter substrate. The striped electrodes are formed on the substrate separately from the column electrodes on the counter substrate. Further, this capacitance is formed by various dielectric films, but when the diode is made of amorphous silicon by plasma CVD, it is formed by a silicon nitride film, a silicon oxide film, a silicon oxynitride film by plasma CVD.

As described above, the display device of the present invention is a matrix type device which has been solved by devising a driving system by inserting a diode in a pixel, which has been conventionally difficult. Plasma created at relatively low temperatures
A CVD film can be used, and a glass substrate is used, which is a great advantage in terms of cost performance.

INDUSTRIAL APPLICABILITY The display device of the present invention can be applied as an information display device in various fields because it has a high density and is driven almost statically, a wide viewing angle with a high contrast ratio is realized.

[Brief description of drawings]

 FIG. 1 is a block diagram of a pixel of a conventional display device. FIG. 2 is a block diagram of one pixel in the display device of the present invention. FIG. 3 is a drive waveform diagram of an embodiment of the display device of the present invention. FIG. 4 is a drive waveform diagram of a reference example of the present invention. (1) …… First row electrode (6) …… Second row electrode (2) …… Column electrode (3) …… First diode (7) …… Second diode (4) …… Display electrode (5) …… Liquid crystal (8) …… Display voltage storage capacity

Claims (5)

[Claims] 1. A liquid crystal is sandwiched between a substrate having a plurality of row electrodes and a counter electrode substrate having a plurality of column electrodes, the row electrodes and the column electrodes are arranged in a matrix, and two rows have one row electrode. A pixel is provided corresponding to the intersection with the column electrode,
Two diodes connected in series in the forward direction are provided between the first row electrode (1) and the second row electrode (6) which are a pair of row electrodes, and the first diode (3) Is connected to the first row electrode (1), the cathode of the second diode (7) is connected to the second row electrode (6), and the cathode of the first diode (3) and the second The display electrode (4) which is one electrode of the liquid crystal (5) is connected to the connection point of the anode of the diode (7), the other electrode of the liquid crystal (5) is connected to the column electrode (2), and the liquid crystal ( The voltage between the display electrode potential Vd, which is the signal potential of the display electrode (4) of 5), and the pixel signal potential of the column electrode applied to the other electrode of the liquid crystal (5) is the liquid crystal voltage V _LC (liquid crystal voltage V _LC ). _LC
= Display electrode potential Vd−pixel signal potential of the column electrode applied to the other electrode) and performing AC drive, and a pixel selection period in which a certain row electrode is selected and another row electrode One frame period is composed of a non-selection period in which is selected, and an alternating potential is applied between the display electrode (4) of the liquid crystal (5) and the other electrode in the two frame periods to perform AC driving. The signal potential V _r ^k ₁ of the first row electrode and the signal potential V _r ^k ₂ of the second row electrode are set to substantially the same potential during the pixel selection period in the pixel of row k and column l. The potentials V _r ^k ₁ and V _r ^k ₂ of the _two row electrodes in the pixel selection period S1 of one of the frame periods are set to the first selection potential V1, and at this time, the first display electrode potential Vd _S1 is The electric potentials V _r ^k ₁ and V 2 of the two row electrodes in the pixel selection period S2 of the other frame period. _r ^k ₂ is the second selection potential V2, at this time the second display electrode potential Vd _S2 is determined (second selection potential V2> first selection potential V1), and the pixel signal of the column electrode The potential V _c ^l is changed according to the pixel, and is set to a desired voltage value satisfying the relationship of the second selection potential V 2 ≧ the pixel signal potential V _c ^{l of the} column electrode ≧ the first selection potential V 1, and the pixel selection is performed. pixel signal pixel signal voltage V _c ^l first row electrode potential in the period S1 V _c ^l _-S1, the second pixel signal potential pixel signal voltage V _c ^l of column electrodes in a pixel selection period S2 V _c ^l _- in _S2 the pixel selection period S1, the row electrode is selected when, S2, the first display electrode potential Vd _S1 - the first pixel signal voltage V _c ^l _-S1 =
-1 ((second display electrode potential Vd _S2 -second pixel signal potential
V _c ^l _-S2 ), and in the non-selection periods H1 and H2 following the pixel selection periods S1 and S2, respectively, l
The pixel signal potential V _c ^l of the column electrode of the column is changed according to the pixel selection period of the row electrodes other than the k row, and at this time, k
The potential applied to the two row electrodes of the row is the signal potential V _r ^k _{2 of the second} row electrode> the pixel signal potential V _{c of the} column electrode.
^l + the liquid crystal voltage V _LC applied in the selection period> the signal potential V _r ^k ₁ of the first row electrode is satisfied, and the non-selection period H1 in one frame period is satisfied.
In a display device substantially equal polarity absolute value thereof to the liquid crystal voltage V _LC held by the non-selection period H2 of the liquid crystal voltage V _LC and the other frame period is characterized by comprising been inverted to be retained. 2. Between the display electrode (4) and the column electrode (2),
The display device according to claim 1, further comprising a display voltage storage capacity (8). 3. A display device according to claim 1, wherein the diode used is a PIN junction diode made of polycrystalline silicon. 4. The display device according to claim 1 or 2, wherein the diode used is a PIN junction diode made of amorphous silicon. 5. The display device according to any one of claims 1 to 4, wherein the substrate used is glass.