CN217404844U - Capacitance compensation circuit, touch panel and electronic equipment - Google Patents
Capacitance compensation circuit, touch panel and electronic equipment Download PDFInfo
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- CN217404844U CN217404844U CN202123152275.1U CN202123152275U CN217404844U CN 217404844 U CN217404844 U CN 217404844U CN 202123152275 U CN202123152275 U CN 202123152275U CN 217404844 U CN217404844 U CN 217404844U
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Abstract
The application provides a capacitance compensation circuit, touch panel and electronic equipment, capacitance compensation circuit includes: the inverting input end of the operational amplifier is used for being connected with the sensor electrode, and the non-inverting input end of the operational amplifier is used for being connected with an excitation signal; a feedback capacitor connected between an inverting input terminal of the operational amplifier and an output terminal of the operational amplifier; the input end of the operational amplifier is connected with a compensation signal, the compensation signal is used for offsetting a parasitic capacitance value of the sensor electrode, and the operational amplifier is used for outputting a capacitance value change signal generated on the sensor electrode after offsetting the parasitic capacitance value. The utility model also provides a touch panel's capacitance compensation method offsets touch panel's parasitic capacitance through the input compensation signal at operational amplifier's input to reach the purpose that reduces chip area.
Description
Technical Field
The application relates to the technical field of touch control, in particular to a capacitance compensation circuit, a touch panel and electronic equipment.
Background
The capacitive touch screen is formed by sticking a layer of transparent special metal conductive substance on the surface of glass. When a finger touches the metal layer, the capacitance of the contact point changes, so that the frequency of an oscillator connected with the contact point changes, and the touch position can be determined by measuring the frequency change to obtain information.
In a human-computer interface, a capacitive Touch control technology is often used to input information, and at present, a Touch screen control Chip mostly uses an Integrated Circuit Chip (IC Chip) of a TDDI (Touch and Display Driver Integration). In TDDI's IC, integrated touch control circuit and display drive circuit, wherein touch control circuit adopts the method of self capacitance detection to detect the state of touch point usually, because self capacitance touch screen is provided with the sensor electrode to form each channel capacitance, detect the capacitance value change of channel capacitance by self capacitance detection circuit, and then can change according to the capacitance value of channel capacitance, reachd the touch condition of touch point.
In order to eliminate the influence of the parasitic capacitance of the sensor and the source line, a signal with the same amplitude as that of the positive terminal is usually applied to the source to eliminate the capacitance, but the influence of the sensor electrode on the parasitic capacitance of the ground cannot be eliminated, and a compensation circuit is usually arranged inside the IC to eliminate the capacitance, wherein the compensation circuit comprises a compensation capacitance usually within 10pF, and occupies a large area, thereby further increasing the area of the IC chip.
SUMMERY OF THE UTILITY MODEL
An object of the embodiments of the present application is to provide a capacitance compensation circuit, a touch panel and an electronic device, which cancel a parasitic capacitance of the touch panel by inputting a compensation signal at an input terminal of an operational amplifier, so as to achieve a purpose of reducing a chip area.
A first aspect of an embodiment of the present application provides a capacitance compensation circuit of a touch panel, including: the inverting input end of the operational amplifier is used for being connected with the sensor electrode, and the non-inverting input end of the operational amplifier is used for being connected with an excitation signal; a feedback capacitor connected between an inverting input terminal of the operational amplifier and an output terminal of the operational amplifier; the reset switch is connected in parallel with the feedback capacitor; one end of the first switch is connected with the inverting input end of the operational amplifier, and the other end of the first switch is connected with the sensor electrode; and one end of the second switch is connected with the sensor electrode, and the other end of the second switch is used for accessing an excitation signal.
In an embodiment, when the excitation signal is at a low level, the reset switch and the second switch are closed, and the first switch is opened, so as to charge a parasitic capacitor of the touch panel.
In an embodiment, when the driving signal changes from a low level to a high level, the reset switch and the second switch are turned off, the first switch is turned on, and the input terminal of the operational amplifier is connected to a first compensation signal to charge a parasitic capacitor of the touch panel, so as to sample a first output voltage of the operational amplifier.
In one embodiment, sampling the first output voltage of the operational amplifier further comprises: and when the excitation signal is at a high level, the reset switch and the second switch are closed, and the first switch is opened, so that the parasitic capacitance of the touch panel is charged.
In one embodiment, the method further comprises: when the excitation signal changes from a high level to a low level, the reset switch and the second switch are opened, the first switch is closed, a second compensation signal is connected to the input end of the operational amplifier to charge a parasitic capacitor of the touch panel, and a second output voltage of the operational amplifier is sampled, wherein the second compensation signal is equal to and opposite to the first compensation signal in phase;
determining a third output voltage of the operational amplifier based on the first output voltage and the second output voltage.
In one embodiment, the magnitude of the compensation signal is calculated by the following formula:
wherein, V OS For the magnitude of the compensation signal, C sense Is the capacitance of the sensor electrode, C base1 Is a first parasitic capacitance, C, between the sensor electrode and the source line base2 Is a second parasitic capacitance between the source line and ground, C fb For said feedback capacitance, VSTIM H For high values of said excitation signal, VSTIM L Is a low value of said excitation signal, V OUT Is the third output voltage of the operational amplifier.
A second aspect of the embodiments of the present application provides a touch panel, including: the capacitance compensation circuit of the touch panel according to the first aspect of the embodiment of the present application and any embodiment thereof.
A third aspect of embodiments of the present application provides an electronic device, including: the touch panel provided by the third aspect of the embodiment of the present application.
The capacitance compensation circuit, the touch panel and the electronic device provided by the application offset the parasitic capacitance of the touch panel by inputting the compensation signal at the input end of the operational amplifier, so that the purpose of reducing the area of a chip is achieved.
Drawings
To more clearly illustrate the technical solutions of the embodiments of the present application, the drawings that are required to be used in the embodiments of the present application will be briefly described below, it should be understood that the following drawings only illustrate some embodiments of the present application and therefore should not be considered as limiting the scope, and that those skilled in the art can also obtain other related drawings based on the drawings without inventive efforts.
FIG. 1A is a schematic diagram of an electronic device according to an embodiment of the present application;
FIG. 1B is a schematic diagram of a touch panel according to an embodiment of the present application;
fig. 2 is a schematic diagram of a capacitance compensation circuit of a touch panel according to an embodiment of the present disclosure;
fig. 3 is a schematic diagram of a capacitance compensation circuit of a touch panel according to an embodiment of the present disclosure;
fig. 4 is a schematic diagram illustrating a compensation result of a capacitance compensation circuit of a touch panel according to an embodiment of the present application.
Detailed Description
The technical solutions in the embodiments of the present application will be described below with reference to the drawings in the embodiments of the present application. In the description of the present application, the terms "first," "second," and the like are used solely to distinguish one from another and are not to be construed as indicating or implying relative importance.
As shown in fig. 1A, the present embodiment provides an electronic device 1 including: at least one processor 11, a memory 12, a touch panel 100 and a capacitance compensation circuit 200 of the touch panel 100, for example, one processor is illustrated in fig. 1. The processor 11, the memory 12, the touch panel 100, and the capacitance compensation circuit 200 are connected by a bus 10. The memory 12 stores instructions executable by the processor 11, and the instructions are executed by the processor 11, so that the electronic device 1 can execute all or part of the processes of the methods in the embodiments described below, and input the compensation signal at the input end of the operational amplifier to cancel the parasitic capacitance of the touch panel, thereby achieving the purpose of reducing the chip area.
As shown in fig. 1B, the present embodiment provides a touch panel, including: the touch panel 100 and the capacitance compensation circuit 200 connected thereto, wherein the touch panel 100 may be a self-capacitance touch panel. The touch panel is provided with sensor electrodes 101 for generating different capacitance values according to a sensing signal to the touch panel. The capacitance compensation circuit 200 is connected to a compensation signal at an input terminal of the operational amplifier for canceling a parasitic capacitance of the touch panel, thereby achieving a purpose of reducing a chip area.
As shown in fig. 2, the present embodiment provides a capacitance compensation circuit 200, which can be applied to the application scenario shown in fig. 1, and the apparatus includes: operational amplifier 210, feedback capacitor 220, reset switch 230, first switch 240, second switch 250.
The operational amplifier 210 includes a positive input terminal, a negative input terminal, and an output terminal;
the feedback capacitor 220 is used to solve the problems of large gain of high-frequency noise of the operational amplifier and unstable system caused by the parasitic capacitance of the touch panel 100.
The switch 230, the first switch 240, and the second switch 250 are reset and selectively turned on or off according to a level state of the excitation signal.
As shown in fig. 3, the present embodiment provides a capacitance compensation circuit 200 of a touch panel, as can be seen from fig. 3, an operational amplifier 210, an inverting input terminal of which is used for connecting to the sensor electrode 101, and a non-inverting input terminal of which is used for accessing to a stimulation signal;
a feedback capacitor 220 connected between the inverting input terminal and the output terminal of the operational amplifier 210;
the reset switch 230 is connected in parallel to the feedback capacitor 220, when the circuit is reset, the reset switch 230 is closed, and at the moment, the voltage at two ends of the feedback capacitor 220 is 0, that is, the input signal is sampled, and the amplification function is not performed; when the reset switch 230 is turned off, the sampled signal is amplified, and the amplification requires a certain time, and the amplification process is a charge conversion process and requires a playback current, so that the output has a certain accuracy.
In one embodiment, Mos transistors may be used as the reset switches.
In one embodiment, the reset circuit can be started in three ways, namely, the reset operation is carried out immediately when the circuit is powered on; secondly, manual operation can be performed when necessary; and thirdly, the operation is automatically carried out according to the requirements of a program or a circuit.
A first switch 240 having one end connected to the inverting input terminal of the operational amplifier and the other end connected to the sensor electrode;
and a second switch 250, one end of which is connected with the sensor electrode and the other end of which is used for connecting in the excitation signal.
The first parasitic capacitance 270 is the parasitic capacitance between the sensor electrode and the source line, typically up to 200 pF.
The second parasitic capacitance 280 is the parasitic capacitance between the source line and ground.
In order to eliminate the first parasitic capacitance and the second parasitic capacitance, the operation principle of the capacitance compensation circuit 200 is as follows:
1: in the first reset phase, the excitation signal is set to a low level, the reset switch and the second switch are closed, and the first switch is opened.
In this embodiment, a low-level driving signal is used as an input signal of an input terminal of the operational amplifier, after the reset switch and the second switch are closed and the first switch is opened, the lower plate of the first parasitic capacitor is connected to the low-level driving signal, and at the same time, the operational amplifier is connected in a unity gain buffer manner, at the phase, the second parasitic capacitor and the first parasitic capacitor are charged, and the charged voltage values are the low-level value VSTIM of the driving signal L 。
2: when the first excitation signal changes from low level to high level in the first integration phase, the input end of the operational amplifier inputs a first compensation signal, the reset switch and the second switch are opened, and the first switch is closed so as to sample the first output voltage of the operational amplifier.
In this embodiment, inputting the first compensation signal to the input terminal of the operational amplifier means applying an offset voltage Vos to the operational amplifier, and the feedback capacitor charges the first parasitic capacitor and the second parasitic capacitor, and the operational amplifier outputs the first voltage value. The first output voltage is the voltage value output by the operational amplifier when the first driving signal changes from low level to high level, and can be denoted as Vout _ H.
3: and in the second reset phase, setting the excitation signal to be high level, closing the reset switch and the second switch, and opening the first switch.
In this embodiment, when the driving signal is set to be at a high level, the reset switch and the second switch are closed, and the first switch is opened, the lower plate of the first parasitic capacitor will be connected to the driving signal at the high level, and meanwhile, the operational amplifier will be in the form of unity gain buffer, at this phase, the second parasitic capacitor and the first parasitic capacitor will be charged, and the charged voltage values are VSTIM value at the high level of the driving signal H 。
4: and when the second excitation signal changes from a high level to a low level in the second integration phase, the input end of the operational amplifier inputs a second compensation signal, the reset switch and the second switch are opened, and the first switch is closed so as to sample a second output voltage of the operational amplifier.
In this embodiment, the second compensation signal and the first compensation signal are in equal-magnitude and opposite-phase, when the second compensation signal is added to the input terminal of the operational amplifier, the feedback capacitor charges the first parasitic capacitor and the second parasitic capacitor, and the operational amplifier outputs the second voltage. The second output voltage is the voltage value output by the operational amplifier when the second driving signal changes from high level to low level, and can be denoted as Vout _ L.
5: a third output voltage of the operational amplifier is determined based on the first output voltage and the second output voltage.
In this embodiment, the third output voltage of the operational amplifier is calculated by:
Vout＝Vout_H–Vout_L
vout is the third output voltage of the operational amplifier, Vout _ H is the first output voltage of the operational amplifier, and Vout _ L is the second output voltage of the operational amplifier.
6: and calculating the magnitude of the compensation signal according to the third output voltage of the operational amplifier.
In this embodiment, the magnitude of the compensation signal is calculated according to the conservation of charge law of the inverting terminal of the operational amplifier, and when the pumping signal is a rising edge, the charge of the negative terminal of the operational amplifier AMP at the first reset phase is:
(C base2 +C sense )*VSTIM L +C fb *V OS
in the first integration phase, the charge at the negative end of the operational amplifier AMP is:
(C base2 +C sense )(VSTIM H -V OS )+(VSTIM H -V OS )+C base1 *(-V OS )+C fb *(VSTIM H -V OS -V OUT )
wherein Vout is the thirdOutput voltage, C fb For feedback capacitance, C base2 Is a second parasitic capacitance, C sense Being equivalent capacitance of sensor, VSTIM L Value of stimulus signal at Low level, VSTIM H Is the value of the excitation signal at the high level.
From the conservation of charge, we obtain:
therefore, as long as it is applied to C base1 The difference between the amplitude of the first pumping signal and the amplitude of the signal applied to the operational amplifier AMP maintains the value of Vos, thereby eliminating unwanted parasitic capacitance.
In one embodiment, assume C base1 ＝200pF，C base2 ＝5pF，C sense ＝1pF，C fb ＝3pF；VSTIM L ＝0，VSTIM H The required value of Vos is 0.212V for setting Vout to 3V at 6V, and as shown in fig. 4, Vos is 0.212V, and in the case where compensation is not required, the resulting Vout voltage is 3V, omitting the compensation circuit.
Although the embodiments of the present invention have been described with reference to the accompanying drawings, those skilled in the art may make various modifications and variations without departing from the spirit and scope of the invention, and such modifications and variations fall within the scope defined by the appended claims.
Claims (5)
1. A capacitance compensation circuit of a touch panel having sensor electrodes, comprising:
the inverting input end of the operational amplifier is used for being connected with the sensor electrode, and the non-inverting input end of the operational amplifier is used for being connected with an excitation signal;
a feedback capacitor connected between an inverting input terminal of the operational amplifier and an output terminal of the operational amplifier;
the input end of the operational amplifier is connected with a compensation signal, the compensation signal is used for offsetting a parasitic capacitance value of the sensor electrode, and the operational amplifier is used for outputting a capacitance value change signal generated on the sensor electrode after offsetting the parasitic capacitance value.
2. The capacitance compensation circuit of a touch panel according to claim 1, further comprising:
and the reset switch is connected in parallel with the feedback capacitor.
3. The capacitance compensation circuit of a touch panel according to claim 2, further comprising:
one end of the first switch is connected with the inverting input end of the operational amplifier, and the other end of the first switch is connected with the sensor electrode;
and one end of the second switch is connected with the sensor electrode, and the other end of the second switch is used for accessing an excitation signal.
4. A touch panel, comprising: the capacitance compensation circuit of the touch panel according to any one of claims 1 to 3.
5. An electronic device, comprising: the touch panel as recited in claim 4.
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| Application Number | Priority Date | Filing Date | Title |
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| CN202123152275.1U CN217404844U (en) | 2021-12-14 | 2021-12-14 | Capacitance compensation circuit, touch panel and electronic equipment |
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| Application Number | Priority Date | Filing Date | Title |
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| CN202123152275.1U CN217404844U (en) | 2021-12-14 | 2021-12-14 | Capacitance compensation circuit, touch panel and electronic equipment |
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| CN217404844U true CN217404844U (en) | 2022-09-09 |
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN116301423A (en) * | 2023-02-28 | 2023-06-23 | 湖南锐阳电子科技有限公司 | Touch array reading circuit and method |
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2021
- 2021-12-14 CN CN202123152275.1U patent/CN217404844U/en active Active
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN116301423A (en) * | 2023-02-28 | 2023-06-23 | 湖南锐阳电子科技有限公司 | Touch array reading circuit and method |
| CN116301423B (en) * | 2023-02-28 | 2024-02-09 | 湖南锐阳电子科技有限公司 | Touch array reading circuit and method |
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