JP2013058871A - Touch panel controller, and input device and electronic apparatus using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the detection sensitivity of or shorten the sensing time of a mutual capacitance type input device.SOLUTION: A transmission circuit 20 applies a transmission signal S1 including a plurality of pulse signals to a transmission electrode 10 at every single cycle of sensing. An A/D converter 44 converts a detection voltage Vs depending on an output voltage of an operational amplifier 32 to a digital value at a positive edge of each pulse signal to generate a first data series DR, and converts the detection voltage Vs to a digital value at a negative edge of each pulse signal to generate a second data series DF. A DSP 102 calculates differences between corresponding digital values included in the first data series DR and the second data series DF, respectively, and integrates the differences between the digital values.

Description

  The present invention relates to a mutual capacitance type touch panel.

  In recent years, electronic devices such as computers, mobile phone terminals, PDAs (Personal Digital Assistants), tablet terminals, and digital cameras are mainly provided with input devices for operating electronic devices by touching with a finger or a pen. ing. As such an input device, a mutual capacitance system is known (Patent Document 1).

International Publication No. 09/078944 Pamphlet

  The present invention has been made in such a situation, and one of exemplary purposes of an aspect thereof is to improve detection sensitivity of a mutual capacitor type input device or to shorten sensing time.

  One embodiment of the present invention relates to a touch panel controller that detects a change in capacitance of a capacitive sensor that includes a transmission electrode and a reception electrode that are capacitively coupled to each other. The touch panel controller includes a transmission circuit that applies a transmission signal including a plurality of pulse signals to the transmission electrode for each sensing operation, an operational amplifier in which a predetermined reference voltage is applied to the first input terminal, and an output of the operational amplifier A feedback capacitor provided between the terminal and the second input terminal, and a first switch which is provided between the receiving electrode and the second input terminal of the operational amplifier and which is turned on during the generation of a plurality of pulse signals. And generating a first data series by converting a detection voltage corresponding to the output voltage of the operational amplifier into a digital value for each positive edge of each pulse signal, and for each negative edge of each pulse signal, the detection voltage An A / D converter that generates a second data series by converting the signal into a digital value.

  According to this aspect, since the first data series is generated corresponding to the positive edge of each pulse and the second data series is generated corresponding to the negative edge of each pulse, the two data series are used. The amount of information is doubled compared to the case of acquiring only positive edges or only negative edges. Therefore, compared with the case where only one edge is used, the sensing time can be shortened or the sensitivity at the same sensing time can be improved.

The touch panel controller according to an aspect may further include an arithmetic processing unit that calculates a difference between digital values corresponding to each other included in each of the first data series and the second data series and integrates the difference between the digital values.
By calculating the difference between the first data series and the second data series, low-frequency in-phase noise superimposed on the first data series and the second data series can be removed.

  The touch panel controller according to an aspect may further include a filter that receives an output voltage of the operational amplifier and removes a frequency higher than a predetermined cutoff frequency.

  Another aspect of the present invention relates to an input device. The input device includes a capacitance sensor including a transmission electrode and a reception electrode that are capacitively coupled to each other, and the above-described touch panel controller that detects a change in capacitance of the capacitance sensor.

  Still another embodiment of the present invention relates to an electronic device. The electronic apparatus includes a capacitive sensor including a transmission electrode and a reception electrode that are capacitively coupled to each other, and the above-described touch panel controller that detects a change in capacitance of the capacitive sensor.

  Note that any combination of the above-described components, or a conversion of the expression of the present invention between methods, apparatuses, and the like is also effective as an aspect of the present invention.

  According to an aspect of the present invention, the detection sensitivity of a mutual capacitor type capacitance sensor can be improved, or the sensing time can be shortened.

It is a block diagram which shows the structure of an electronic device provided with the touch-type input device which concerns on embodiment. It is a circuit diagram which shows the structure of the input device which has the touchscreen controller which concerns on embodiment. It is a time chart which shows operation | movement of the touch panel controller which concerns on embodiment. It is a time chart which shows operation | movement of a touch panel controller when external noise mixes. It is a circuit diagram which shows the structure of the capacity | capacitance detection circuit which concerns on a modification.

  The present invention will be described below based on preferred embodiments with reference to the drawings. The same or equivalent components, members, and processes shown in the drawings are denoted by the same reference numerals, and repeated descriptions are omitted as appropriate. The embodiments do not limit the invention but are exemplifications, and all features and combinations thereof described in the embodiments are not necessarily essential to the invention.

In this specification, “the state in which the member A is connected to the member B” means that the member A and the member B are electrically connected to each other in addition to the case where the member A and the member B are physically directly connected. It includes cases where the connection is indirectly made through other members that do not substantially affect the general connection state, or that do not impair the functions and effects achieved by their combination.
Similarly, “the state in which the member C is provided between the member A and the member B” refers to the case where the member A and the member C or the member B and the member C are directly connected, as well as their electric It includes cases where the connection is indirectly made through other members that do not substantially affect the general connection state, or that do not impair the functions and effects achieved by their combination.

  FIG. 1 is a block diagram illustrating a configuration of an electronic device 1 including a touch input device 2 according to an embodiment. The electronic device 1 is a computer, a mobile phone terminal, a PDA (Personal Digital Assistant), a tablet terminal, or a digital camera. The input device (touch input device) 2 is disposed, for example, at a position overlapping with an LCD (Liquid Crystal Display) 8, that is, on the surface layer of the LCD 8, and functions as a touch panel. Alternatively, it may be an input device such as a track pad arranged at a different location from the LCD 8.

  The input device 2 includes a touch panel (sensor unit) 4 and a touch panel controller 3. The touch panel 4 is a mutual capacitance matrix touch panel, and includes a plurality of transmission electrodes 10 provided for each column of the matrix and a plurality of reception electrodes 12 provided for each column of the matrix. Row and column assignments may be reversed. At each intersection of the transmitting electrode 10 and the receiving electrode 12, the two electrodes are capacitively coupled to each other. A pair of the transmission electrode 10 and the reception electrode 12 at each intersection forms one capacitive sensor 5. That is, the touch panel 4 includes a plurality of capacitive sensors 5 arranged in a matrix. When an object 6 such as a user's finger or pen touches or approaches a certain capacitance sensor 5, the mutual capacitance formed by the capacitance sensor 5 changes.

  The touch panel controller 3 includes a capacitance detection circuit 100 and a DSP (Digital Signal Processor) 102.

  The capacitance detection circuit 100 applies a transmission signal cyclically to the plurality of transmission electrodes 10 in order, and selects a column to be subjected to capacitance detection. The capacitance detection circuit 100 detects a change in capacitance formed between the selected transmission electrode 10 and each of the plurality of reception electrodes 12.

  FIG. 2 is a circuit diagram showing a configuration of the input device 2 having the touch panel controller 3 according to the embodiment. Although FIG. 2 shows the touch panel 4 having one transmission electrode 10 and a plurality of reception electrodes 12 orthogonal thereto, a plurality of transmission electrodes 10 may be provided.

A transmission electrode 10, a plurality of receiving electrodes ₁₂ 1 to 12 _m are respectively capacitively coupled, between them, the capacitive sensor ₅ 1 to 5 _m comprising a mutual capacitance _{C M} is formed. The capacitance detection circuit 100 includes a transmission circuit 20, an initialization circuit 33, an amplification circuit 30, a filter 36, a sample hold circuit 40, an amplifier 42, an A / D converter 44, and a control unit 50. Capacitance detection circuit 100 sequentially sensing a change in the plurality of capacitive sensors _{5 1 to m} each mutual capacitance _{C M.}

The capacitance detection circuit 100 includes a transmission terminal (TX terminal) and a reception terminal (RX terminal) provided for each reception electrode 12. The TX terminal of the capacitance detection circuit 100 is connected to the transmission electrode 10, and each RX _i terminal of the capacitance detection circuit 100 is connected to the corresponding reception electrode 12 _i .

The transmission circuit 20 applies a transmission signal S1 including a plurality of pulse signals to the transmission electrode 10 _i for each sensing. The signal generator 22 generates a periodic clock signal. The driver 24 receives the clock signal and outputs a transmission signal S1 synchronized therewith to the transmission electrode 10. Transmission signal S1 is a periodic signal that alternately repeats a first voltage level (for example, power supply voltage Vdd) and a second voltage level (for example, ground voltage Vss). In the touch panel 4 provided with a plurality of transmission electrodes 10, the transmission signal S <b> 1 is applied to the selected transmission electrode 10, and a fixed voltage level, for example, the ground voltage Vss is applied to the other transmission electrodes 10.

Amplifier circuit 30 detects the amount of change in the mutual capacitance C _M of the capacitive sensor 5 _{1 to m} in which a plurality of receiving electrodes 12 respectively formed. The amplifier circuit 30 includes an operational amplifier 32, a feedback capacitor C _FB , a drive buffer 34, a first switch SW1, and a third switch SW3.

A predetermined reference voltage V _REF is applied to the first input terminal (non-inverting input terminal) of the operational amplifier 32. The feedback capacitor C _FB is provided between the output terminal of the operational amplifier 32 and its second input terminal (inverting input terminal).

Each of the plurality of first switch _{SW1 1 to m,} is provided for each receiving electrode _{12 1 to m.} The first switch SW1 _i is provided between the corresponding receiving electrode 12 _i and the inverting input terminal of the operational amplifier 32. Each first switch SW1 _i is in an ON state during a period in which a plurality of pulse signals of the transmission signal S1 are generated when the corresponding capacitive sensor 5 is a sensing target.

A plurality of third switches SW3 1- _m are also provided for each of the receiving electrodes _121-m . The third switches SW31 to _m are turned on when the capacitance detection circuit 100 is in an inoperative state, and are provided to fix the potentials of the lines to which the third switches SW31 to _m are connected.

The plurality of first switches SW11 to _SWm can be grasped as a selector (multiplexer) MUX for selecting the reception electrode 12 to be detected.

Prior to sensing, the initialization circuit 33 initializes the potential of the receiving electrode 12 to the reference voltage _VREF . The initialization circuit 33 includes a feedback resistor R _FB provided in parallel with the feedback capacitor C _FB between the output terminal of the operational amplifier 32 and its second input terminal (inverting input terminal).

When the transmission signal S1 is applied, it is charged mutual capacitance C _M is, charge is stored in accordance with the capacitance value. When the voltage level of the transmission signal S1 is changed, the charge stored in the mutual capacitance C _M is charged and discharged, current I _RX is generated. The amplifier circuit 30 generates a detection voltage Vs corresponding to the current I _RX .

  The low pass filter 46 filters the detection voltage Vs from the operational amplifier 32. The cut-off frequency of the low-pass filter 46 is set higher than the transmission frequency of the transmission circuit 20, and removes high-frequency noise contained in the detection voltage Vs.

  The sample hold circuit 40 samples and holds the detection voltage Vs that has passed through the low pass filter 46. The amplifier 42 amplifies the detection voltage Vs sampled and held as necessary. The A / D converter 44 converts the amplified detection voltage Vs into a digital value Ds. This digital value Ds indicates a change in capacitance of each capacitance sensor 5.

  The sample hold circuit 40 samples and holds the detection voltage Vs corresponding to the output voltage of the operational amplifier 32 for each positive edge (also referred to as a rising edge or a leading edge) of each pulse signal of the transmission signal S 1, and the A / D converter 44. Generates the first data series DR by converting the sampled and held detection voltage Vs into a digital value Ds. The sample hold circuit 40 samples and holds the detection voltage Vs for each negative edge (also referred to as a falling edge or a trailing edge) of each pulse signal of the transmission signal S1, and the A / D converter 44 is sampled and held. A second data series DF is generated by converting the detection voltage Vs into a digital value Ds. The timing of sample and hold by the sample and hold circuit 40 is set a predetermined time after the positive edge and the negative edge. When the A / D converter 44 has a sample and hold function, the sample and hold circuit 40 may be omitted.

  The control unit 50 performs sequence control on the ON / OFF state of the transmission circuit 20, the first switch SW1, and the third switch SW3, the sample hold operation of the sample hold circuit 40, and the conversion operation of the A / D converter 44.

  The first data series DR and the second data series DF generated by the capacity detection circuit 100 are input to the DSP 102 at the subsequent stage. The DSP 102 includes a first data series DR and a second data series DF.

  The DSP 102 calculates a difference between digital values corresponding to each other included in each of the first data series DR and the second data series DF to generate a difference data series DD. The DSP 102 integrates (integrates) the elements of the difference data series DD, which is the difference between the digital values.

The above is the configuration of the touch panel controller 3. Next, the operation will be described. FIG. 3 is a time chart showing the operation of the touch panel controller 3 according to the embodiment. The switch state indicates that the high level is on and the low level is off. Here simplicity of explanation, for ease of understanding, attention is paid to one of the receiving electrodes 12, the operation will be described for detecting the mutual capacitance C _M to it form.

The first switch SW1 is turned on at time t0. Immediately before the first switch SW1 is turned on, the potential of the inverting input terminal (−) of the operational amplifier 32 becomes equal to the reference voltage V _REF by feedback of the feedback resistor _RFB . Further, the output voltage Vs of the operational amplifier 32 is also equal to the reference voltage _VREF . When the first switch SW1 is turned on in this state, the voltage of the receiving electrode 12 is initialized to the reference voltage _VREF .

During one sensing, the transmission signal S1 includes N pulse signals P _{1 to} P _N. The first switch SW1 is kept on during a period in which _N pulse signals P _{1 to} P _N are generated. A current I _RX flows from the reception electrode 12 via the RX terminal in accordance with the positive edge and the negative edge of each of the pulse signals P _{1 to} P _N. When mutual capacitance _{C M} is large, the amplitude of the current _{I RX} increases, when mutual capacitance CM is small, the amplitude of the current _{I RX} decreases. The direction of the current I _RX is opposite between the positive edge and the negative edge of the transmission signal S1.

When the current I _RX flows in the first direction in response to the positive edges of the pulse signals P _{1 to} P _N , the feedback capacitor C _FB is charged and the detection voltage Vs rises. When the current I _RX flows in the second direction in response to the negative edges of the pulse signals P _{1 to} P _N , the feedback capacitor C _FB is discharged and the detection voltage Vs decreases. As described above, since the magnitude of the current I _RX depends on the mutual capacitance C _M , the detection voltage Vs has an amplitude corresponding to the mutual capacitance C _M.

The sample hold circuit 40 and the A / D converter 44 convert the detection voltage Vs after being fluctuated by the current I _RX corresponding to the positive edge into a digital value for each of the pulse signals P _{1 to} P _N , and the first data series DR Is generated. Further, the sample hold circuit 40 and the A / D converter 44 convert the detection voltage Vs after being fluctuated by the current I _RX corresponding to the negative edge into a digital value for each of the pulse signals P _{1 to} P _N , and the second data series Generate a DF.

The above is the operation of the capacitance detection circuit 100.
According to the capacitance detection circuit 100, the first data series DR is generated corresponding to the positive edge of each pulse, and the second data series DF is generated corresponding to the negative edge of each pulse. By using the series DR and DF, the amount of information is doubled compared to the case of acquiring only positive edges or only negative edges. Therefore, compared with the case where only one edge is used, the sensing time can be shortened or the sensitivity at the same sensing time can be improved.

The DSP 102 calculates a difference between the first data series DR and the second data series DF, generates a difference data series DD, and integrates each data of the difference data series DD.
Digital value DRi and DFi difference corresponding to each other of the first data sequence DR and the second data sequence DF (DRi-DFi) shows the amplitude of the voltage _{V RX} of the receiving electrode 12, i.e., the capacitance value of the mutual capacitance _{C M.} Therefore, the difference value (DRi-DFi) by integrating the _{Σ i = 1: N (DRi} -DFi) is a data corresponding to the capacitance value of the mutual capacitance _{C M.}

  By the above-described processing of the DSP 102, the influence of low frequency noise mixed in the reception electrode 12 can be reduced. Consider a situation in which external noise having a frequency lower than the transmission frequency is superimposed on the reception electrode 12 in addition to the pulse signal. FIG. 4 is a time chart showing the operation of the touch panel controller 3 when external noise is mixed.

Each data of the first data sequence DR includes a component DR in response to a change in the mutual capacitance _{C M} of the capacitive sensor 5, a component Dnoise corresponding to noise. The same applies to each data of the second data series DF. Here, when the frequency of the noise is low, the magnitude of the noise at the timing of the positive edge and the negative edge of the same pulse signal is almost equal and can be regarded as in-phase noise. Therefore, by calculating the difference between the first data series DR and the second data series DF, it is possible to remove the influence of noise and accurately detect the input operation.

  The present invention has been described based on the embodiments. This embodiment is an exemplification, and it will be understood by those skilled in the art that various modifications can be made to combinations of the respective constituent elements and processing processes, and such modifications are within the scope of the present invention. is there. Hereinafter, such modifications will be described.

FIG. 5 is a circuit diagram showing a configuration of a capacitance detection circuit 100a according to a modification. The initialization circuit 33 of the capacitance detection circuit 100a includes a drive buffer 34 and second switches _SW21 to _m .
The drive buffer 34 receives the potential of the inverting input terminal of the operational amplifier 32. For example, the drive buffer 34 is a voltage follower circuit.

The second switches SW2 1 to _m are provided for each of the receiving electrodes ₁₂₁ to _m . The second switch SW2 _i is provided between the corresponding receiving electrode 12 _i and the output terminal of the drive buffer 34. The second switch SW2 _i is turned on prior to sensing.

Also with this configuration, the same effect as that of the capacitance detection circuit 100 of FIG. 2 can be obtained. 2 does not require the drive buffer 34 and the second switches SW21 to _m , and therefore has an advantage that the circuit area is smaller than that in FIG.

  Although the present invention has been described using specific terms based on the embodiments, the embodiments only illustrate the principles and applications of the present invention, and the embodiments are defined in the claims. Many variations and modifications of the arrangement are permitted without departing from the spirit of the present invention.

DESCRIPTION OF SYMBOLS 1 ... Electronic device, 2 ... Input device, 4 ... Touch panel, 5 ... Capacitance sensor, 6 ... Finger, 8 ... LCD, 10 ... Transmission electrode, 12 ... Reception electrode, 20 ... Transmission circuit, 22 ... Driver, 30 ... Amplification circuit 32 ... operational amplifier 34 ... drive buffer _CFB ... feedback capacitor _RFB ... feedback resistor SW1 ... first switch SW2 ... second switch SW3 ... third switch 40 ... sample hold circuit 42 ... amplifier , 43... Differential amplifier, 44... A / D converter, 50... Control unit, 100... Capacitance detection circuit, 102 ... DSP, C _M ... Mutual capacitance, S1.

Claims (7)

A touch panel controller that detects a change in capacitance of a capacitive sensor including a transmission electrode and a reception electrode that are capacitively coupled to each other,
A transmission circuit that applies a transmission signal including a plurality of pulse signals to the transmission electrode for each sensing;
An operational amplifier in which a predetermined reference voltage is applied to the first input terminal;
A feedback capacitor provided between the output terminal of the operational amplifier and its second input terminal;
A first switch that is provided between the reception electrode and the second input terminal of the operational amplifier and is turned on during a period in which the plurality of pulse signals are generated;
For each positive edge of each pulse signal, a detection voltage corresponding to the output voltage of the operational amplifier is converted into a digital value to generate a first data series, and for each negative edge of each pulse signal, the detection voltage is An A / D converter that generates a second data series by converting the digital value;
An arithmetic processing unit for calculating a difference between digital values corresponding to each other included in each of the first data series and the second data series, and integrating the difference between the digital values;
A touch panel controller comprising:   The touch panel controller according to claim 1, further comprising a filter that removes high frequency noise included in an output voltage of the operational amplifier.   The touch panel controller according to claim 1, further comprising an initialization circuit that initializes the potential of the reception electrode prior to the sensing. The initialization circuit includes:
The touch panel controller according to claim 3, further comprising a feedback resistor provided in parallel with the feedback capacitor between the output terminal of the operational amplifier and the second input terminal. The initialization circuit includes:
A drive buffer for receiving a potential of the second input terminal of the operational amplifier;
A second switch provided between the output terminal of the drive buffer and the receiving electrode and turned on prior to sensing;
The touch panel controller according to claim 3, further comprising: A capacitive sensor including a transmit electrode and a receive electrode capacitively coupled to each other;
The touch panel controller according to claim 1, which detects a change in capacitance of the capacitance sensor;
An input device comprising: A capacitive sensor including a transmit electrode and a receive electrode capacitively coupled to each other;
The touch panel controller according to claim 1, which detects a change in capacitance of the capacitance sensor;
An electronic device comprising:

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