WO2018126459A1

WO2018126459A1 - Capacitance measurement circuit and electronic device

Info

Publication number: WO2018126459A1
Application number: PCT/CN2017/070492
Authority: WO
Inventors: 陈圣凯; 文亚南; 杨富强
Original assignee: 深圳市汇顶科技股份有限公司
Priority date: 2017-01-06
Filing date: 2017-01-06
Publication date: 2018-07-12
Also published as: CN109496290A

Abstract

A capacitance measurement circuit (12), comprising: a driving circuit (120) coupled to multiple transmitting electrodes (TX_1-TX_N) and used for generating a driving signal (tx1-txN) for the multiple transmitting electrodes (TX_1-TX_N); an impedance unit (122) coupled to the driving circuit (120) and used for receiving the driving signal (tx1-txN) and for generating multiple virtual electrode signals (rx1'-rxM'), multiple internal impedances (Z_ij_in) being formed in the impedance unit (122), the multiple virtual electrode signals (rx1'-rxM') being associated with the multiple internal impedances (Z_ij_in); and multiple first amplifiers (Amp_pre_1-Amp_pre_M) coupled to multiple receiving electrodes (RX_1~RX_M) and the impedance unit (122), multiple first output signals (Vo_pre_1-Vo_pre_M) outputted by the multiple first amplifiers (Amp_pre_1-Amp_pre_M) being associated with the magnitudes of multiple capacitances (Cij) between the multiple transmitting electrodes (TX_1-TX_N) and the multiple receiving electrodes (RX_1-RX_M).

Description

Capacitance detection circuit and electronic device

Technical field

The present application relates to a capacitance detecting circuit and an electronic device, and more particularly to a capacitance detecting circuit and an electronic device capable of canceling external impedance and eliminating common mode noise.

Background technique

With the advancement of technology, the operational interfaces of various electronic products have gradually become more humanized in recent years. For example, through the touch panel, the user can directly operate on the screen with a finger or a stylus, input information/text/pattern, and save the trouble of using an input device such as a keyboard or a button. In fact, the touch screen usually consists of a sensing panel and a display disposed behind the sensing panel. The electronic device judges the meaning of the touch according to the position touched by the user on the sensing panel and the picture presented by the display at the time, and executes the corresponding operation result.

In recent years, flexible display panels have become more popular in the market due to their flexibility and making certain operations more convenient. However, the capacitance between the electrode disposed on the flexible display screen and the ground terminal is too large, so that the amount of capacitance change caused by the touch on the electrode is not significant, and the touch device cannot distinguish whether it is an effective touch, thereby reducing the product. performance. In addition, the electrodes disposed on the display screen are affected by noise from the display screen, which is a common mode noise, and have a disadvantage that the signal to noise ratio is too low. Therefore, the prior art is necessary for improvement.

Summary of the invention

Accordingly, a primary object of some embodiments of the present invention is to provide a capacitance detecting circuit and an electronic device that can cancel external impedance and eliminate common mode noise to improve the disadvantages of the prior art.

In order to solve the above technical problem, the present application provides a capacitance detecting circuit coupled to a plurality of transmitting electrodes and a plurality of receiving electrodes, the capacitance detecting circuit including a driving circuit coupled to the plurality of transmitting electrodes, Generating a driving signal to the plurality of transmitting electrodes, wherein the plurality of transmitting electrodes and the plurality of receiving electrodes have a plurality of external impedances; an impedance unit coupled to the driving circuit for receiving Driving the signal and generating a plurality of dummy electrode signals, wherein the impedance unit is formed with a plurality of internal impedances, the plurality of virtual electrode signals are related to the plurality of internal impedances; and a plurality of first amplifiers, each The first amplifier has a first input end and a second input end, and the first input end of the plurality of first amplifiers is coupled to the plurality of receiving electrodes, the plurality of first amplifiers The second input end is coupled to the impedance unit, and the plurality of first amplifiers generate a plurality of first output signals; wherein the plurality of first output signals are related to the plurality of transmissions Receiving a plurality of the plurality of the capacitances between the electrodes.

For example, the impedance unit includes at least one capacitor; and at least one resistor coupled to the at least one capacitor, the at least one capacitor and the at least one resistor forming the plurality of internal impedances.

For example, the impedance unit further includes an adjusting unit coupled to the at least one resistor for adjusting a resistance value of the at least one resistor such that an external impedance of the plurality of external impedances and the plurality of internal portions An impedance difference of an internal impedance of the impedance is less than a specific value.

For example, the specific value is 0.4 times the external impedance.

For example, the adjustment unit includes a storage unit, the storage unit stores a plurality of impedance adjustment values, and the adjustment unit adjusts a resistance value of the at least one resistor according to the plurality of impedance adjustment values.

For example, the capacitance detecting circuit further includes a control logic circuit coupled to the memory unit, and the control logic circuit is controlled by a control unit for outputting the plurality of impedance adjustment values.

For example, the storage unit is a Non-Volatile Memory (NVM).

For example, the storage unit is a Volotile Memory.

For example, the capacitance detecting circuit further includes at least one second amplifier coupled to the plurality of first amplifiers for canceling a common mode noise received by the plurality of transmitting electrodes (Common Mode) Noise) to generate at least one second output signal; wherein the at least one second output signal is related to the plurality of capacitance sizes between the plurality of transmitting electrodes and the plurality of receiving electrodes.

For example, the at least one second amplifier is a Programmable Gain Amplifier.

For example, the capacitance detecting circuit further includes a duplexer coupled between the plurality of first amplifiers and the at least one second amplifier.

For example, the capacitance detecting circuit further includes a control logic circuit coupled to the reworker, the control logic circuit is controlled by a control unit for controlling the reworker to A portion of the first output signal of the output signal is passed to an input of the at least one second amplifier.

For example, the drive signal is an alternating current (AC) signal.

The present application further provides an electronic device including a plurality of transmitting electrodes, a plurality of receiving electrodes, and a capacitance detecting circuit coupled to the plurality of transmitting electrodes and the plurality of receiving electrodes, wherein the capacitance detecting circuit includes a driving circuit. The plurality of transmitting electrodes are coupled to the plurality of transmitting electrodes for generating a driving signal to the plurality of transmitting electrodes, wherein the plurality of transmitting electrodes and the plurality of receiving electrodes have a plurality of external impedances; an impedance unit, And coupled to the driving circuit, configured to receive the driving signal, and generate a plurality of virtual electrode signals, wherein the impedance unit is formed with a plurality of internal impedances, and the plurality of virtual electrode signals are related to the plurality of internal electrodes And a plurality of first amplifiers, each of the first amplifiers having a first input end and a second input end, the first input end of the plurality of first amplifiers being coupled to the plurality of receiving electrodes The second input end of the plurality of first amplifiers is coupled to the impedance unit, and the plurality of first amplifiers generate a plurality of first output signals; wherein the plurality of first Signals associated with the plurality of electrodes between the plurality of transfer electrodes receiving the plurality of capacitor size.

DRAWINGS

FIG. 1 is a schematic top view of an electronic device according to an embodiment of the present application.

2 is a schematic diagram of a capacitance detecting circuit according to an embodiment of the present application.

FIG. 3 is a schematic diagram of an impedance unit according to an embodiment of the present application.

detailed description

In order to make the objects, technical solutions, and advantages of the present application more comprehensible, the present application will be further described in detail below with reference to the accompanying drawings and embodiments. It is understood that the specific embodiments described herein are merely illustrative of the application and are not intended to be limiting.

Please refer to FIG. 1. FIG. 1 is a schematic top view of an electronic device 10 according to an embodiment of the present disclosure. The electronic device 10 can be a touch-operated electronic device such as a smart phone, a tablet computer, a smart wearable device, or an in-vehicle display device. The electronic device 10 includes transmission electrodes (or driving electrodes) TX_1 to TX_N, receiving electrodes RX_1 to RX_M, a capacitance detecting circuit 12, a flexible display panel 14, and a control unit 16. The control unit 16 can be a microcontroller/microcontroller unit (MCU). The flexible display 14 is used to display a picture to be displayed by the electronic device 10, which has flexibility. The transmitting electrodes TX_1-TX_N and the receiving electrodes RX_1-RX_M are disposed on/in the flexible display screen 14. The capacitance detecting circuit 12 is coupled to the transmitting electrodes TX_1-TX_N and the receiving electrodes RX_1-RX_M for detecting the transmitting electrodes TX_1-TX_N. The size of the plurality of capacitors between the receiving electrodes RX_1 and RX_M to determine the position at which the touch occurs.

It should be noted that since the flexible display 14 has flexibility, the capacitances corresponding to the transmitting electrodes TX_1 to TX_N and the receiving electrodes RX_1 to RX_M are larger than those of the conventional Rigid Type Panel (usually larger than the hard screen). Nearly 10 times). In order to solve the problem that the capacitances of the transmitting electrodes TX_1-TX_N and the receiving electrodes RX_1-RX_M in the flexible display screen 14 are excessively large, the present application uses the impedance unit of the capacitance detecting circuit 12 to form between the transmitting electrodes TX_1-TX_N and the receiving electrodes RX_1-RX_M. a plurality of internal impedances for canceling a plurality of external impedances between the transmitting electrodes TX_1-TX_N and the receiving electrodes RX_1-RX_M, wherein the plurality of external impedances include the transmitting electrodes TX_1-TX_N and the receiving electrodes RX_1-RX_M with respect to a ground terminal capacitance.

Specifically, please refer to FIG. 2. FIG. 2 is a schematic functional block diagram of a capacitance detecting circuit 12 according to an embodiment of the present disclosure. The capacitor detecting circuit 12 includes a driving circuit 120, an impedance unit 122, a reworker 124, and a logic control circuit. Logic Control Circuit 126, a front end circuit 128, a determination circuit 130, and an amplifier Amp and preamplifiers Amp_pre_1 to Amp_pre_M. The logic control circuit 126 is coupled to the impedance unit 122 and the duplexer 124 for controlling the impedance unit 122 and the duplexer 124 according to the indication of the control unit 16. The driving circuit 120 (via the duplexer 124) is coupled to the transmitting electrodes TX_1-TX_N for generating the driving signals tx1 to txN to the transmitting electrodes TX_1-TX_N, and the driving signals tx1-txN may be alternating currents (AC) having the same waveform. The signal may be an alternating current signal such as a square wave, a triangular wave, a sine wave, or a trapezoidal wave. A plurality of external impedances Z_ex (impedances formed outside the capacitance detecting circuit 12) are formed between the transmitting electrodes TX_1 to TX_N and the receiving electrodes RX_1 to RX_M. For convenience of explanation, FIG. 2 only shows between the transmitting electrode TX_j and the receiving electrode RX_i. The external impedance Z_ij_ex), the receiving electrodes RX_1 to RX_M carry the electrode signals rx1 to rxM, and the electrode signals rx1 to rxM are related to the plurality of external impedances Z_ex. The impedance unit 122 is coupled to the driving circuit 120 for generating a plurality of virtual electrode signals rx1' to rxM' according to the driving signals tx1 to txN. In addition, the impedance unit 122 can form a plurality of internal impedances, where the internal impedance refers to It is an impedance formed within the capacitance detecting circuit 12, and the virtual electrode signals rx1' to rxM' are related to a plurality of internal impedances. Each of the preamplifiers Amp_pre_1 to Amp_pre_M has a first input terminal and a second input terminal. The first input terminals of the preamplifiers Amp_pre_1 to Amp_pre_M are coupled to the receiving electrodes RX_1 RXX_M to receive the electrode signals rx1 r rxM. The second input ends of the amplifiers Amp_pre_1 ～Amp_pre_M are coupled to the impedance unit 122 to receive the virtual electrode signals rx1 ′ rxm′. The preamplifiers Amp_pre_1 to Amp_pre_M may be differential amplifiers for subtracting the electrode signals rx1 to rxM from the virtual electrode signals rx1' to rxM', respectively, to generate output signals Vo_pre_1 to Vo_pre_M, in other words, The output signal Vo_pre_m is related to (proportional to) a difference between the electrode signal rxm and the virtual electrode signal rxm', that is, the output signal Vo_pre_m can be expressed as Vo_pre_m=Av(rxm-rxm')+n, where Av represents the preamplifier Amp_pre_m A gain, n represents noise, which may include/represent a common mode noise (Common Mode Noise) received by the receiving electrode RX_m. The output signals Vo_pre_1 to Vo_pre_M are related to the magnitudes of the plurality of capacitances between the transmission electrodes TX_1 to TX_N and the reception electrodes RX_1 to RX_M.

In detail, the impedance unit 122 may form a plurality of internal impedances to cancel a plurality of external impedances between the transmitting electrodes TX_1 to TX_N and the receiving electrodes RX_1 to RX_M. For example (transfer electrode The external impedance Z_ij_ex between the TX_j and the receiving electrode RX_i is taken as an example. Since the transmitting electrode TX_j receives the driving signal txj, the electrode signal rxi at the receiving electrode RX_i is related to txj*Z_ij_ex (for convenience of explanation, the electrode signal rxi will be described in the following description. The simplified representation is rxi=txj*Z_ij_ex). In this case, the impedance unit 122 can form an internal impedance Z_ij_in inside the capacitance detecting circuit 12, and generate a virtual electrode signal rxi' according to the driving signal txj (where the virtual electrode signal rxi' can be simplified as rxi=txj*Z_ij_in), The preamplifier Amp_pre_m can subtract the electrode signal rxi from the virtual electrode signal rxi' to generate the output signal Vo_pre_m, and the output signal Vo_pre_m can be expressed as Vo_pre_m=Av*txj*(Z_ij_ex-Z_ij_in). It should be noted that for the output of the preamplifier Amp_pre_m, the impedance equivalent to the transfer electrode TX_j and the receive electrode RX_i is only (Z_ij_ex-Z_ij_in), in other words, when the true external impedance Z_ij_ex is large. The impedance unit 122 can be utilized to form the internal impedance Z_ij_in to cancel the true external impedance Z_ij_ex such that the impedance seen at the output of the preamplifier Amp_pre_m (and its back end circuit) is only (Z_ij_ex-Z_ij_in). In an embodiment, a difference between the external impedance Z_ij_ex and the internal impedance Z_ij_in is less than 0.4 times the external impedance Z_ij_ex, ie Z_ij_ex-Z_ij_in<0.4*Z_ij_ex. Of course, this multiple relationship is only for illustration, and can be set to other values. In addition, the equivalent circuit of the external impedance Z_ij_ex is as shown in FIG. 2. The external impedance Z_ij_ex includes capacitors Cij, Cdg, Csg and resistors Rd, Rs, wherein the capacitance Cij represents the mutual capacitance between the transmitting electrode TX_j and the receiving electrode RX_i (Mutual Capacitance) The capacitor Cdg represents the capacitance of the transmitting electrode TX_j to the ground, the capacitor Csg receives the capacitance of the electrode RX_i to the ground, the resistor Rd represents the equivalent resistance corresponding to the transmitting electrode TX_j, and the resistor Rs represents the equivalent resistance corresponding to the receiving electrode RX_i.

Please refer to FIG. 3. FIG. 3 is a schematic diagram of an impedance unit 122 according to an embodiment of the present application. In the embodiment of FIG. 3, the impedance unit 122 can form an internal impedance Z_ij_in. To form the internal impedance Z_ij_in, the impedance unit 122 can include capacitors Cij', Cdg', Csg', resistors Rd', Rs', and an adjustment unit 30, The adjusting unit 30 can be coupled to the resistors Rd', Rs' for adjusting the resistance values of the resistors Rd', Rs' such that the internal impedance Z_ij_in formed by the impedance unit 122 satisfies Z_ij_ex-Z_ij_in<0.4*Z_ij_ex or other relationship. In addition, the adjustment unit 30 includes a storage unit 32, which stores The storage unit 32 stores impedance adjustment values corresponding to the resistors Rd' and Rs', and the adjustment unit 30 adjusts the resistance values of the resistors Rd' and Rs' based on the impedance adjustment value. In a specific embodiment, the storage unit 32 can be a Non-Volatile Memory (NVM), which can be an electrically erasable programmable read only memory (EEPROM), fast. Flash Memory, One-Time Programmable Erasable Programmable Read Only Memory (OTP-EPROM) or electronic fuse memory (e-fuse), in other words, The impedance adjustment value may be stored in the memory unit 32 in advance (via the logic control circuit 126) to adjust the resistances Rd', Rs' in the internal impedance Z_ij_in. In addition, in another embodiment, the storage unit 32 can be a volatile memory (Volatile Memory), which can be a Synchronous Dynamic Random Access Memory (SDRAM), and the impedance adjustment value can be controlled by the control unit. 16 is generated and stored in the memory unit 32 by the logic control circuit 126 to adjust the resistors Rd', Rs' in the internal impedance Z_ij_in.

In addition, referring to FIG. 2, the front end circuit 128 may include an anti-alias filter (AAF), a band pass filter (BPF), and an analog-to-digital converter (Analog-to-Digital). The converter circuit (ADC) determines the size of the plurality of capacitors between the transmitting electrodes TX_1 to TX_N and the receiving electrodes RX_1 to RX_M according to the output signal of the analog-to-digital converter to determine the position at which the touch occurs. In addition, the amplifier Amp can be a Programmable Gain Amplifier (PGA), and the amplifier Amp can be used to eliminate the common mode noise received by the receiving electrodes RX_1~RX_M, wherein the common mode noise can come from the display noise of the flexible display screen 14 ( Such as LCD noise). In detail, the amplifier Amp is coupled to the preamplifiers Amp_pre_1 to Amp_pre_M through the duplexer 124, and the duplexer 124 can transmit the K output signals of the output signals Vo_pre_1 to Vo_pre_M to the amplifier Amp to eliminate the receiving electrodes RX_1 to RX_M. Common mode noise, where K can be a multiple of two. Further, the duplexer 124 can be controlled by the logic control circuit 126 (and the logic control circuit 126 can be controlled by the control unit 16), and K output signals whose channel characteristics/noise characteristics are similar, and K The output signal is passed to the amplifier Amp. In this way, not only can the amplification of the output signals Vo_pre_1~Vo_pre_M be related to the touch The semaphore can effectively eliminate the common mode noise, so that the operational amplifier in the amplifier Amp does not enter the saturated state due to noise, and fully utilizes a dynamic range of the analog-to-digital converter and improves Signal-to-Noise Ratio (SNR).

It should be noted that the foregoing embodiments are used to explain the concept of the present application, and those skilled in the art can make various modifications, and are not limited thereto. For example, the capacitance detecting circuit is not limited to include only one programmable gain amplifier. The capacitance detecting circuit of the present application may include a plurality of programmable gain amplifiers, as long as the input end (through the duplexer) is coupled to the output of the preamplifier, The Parallel Processing method eliminates common mode noise and also satisfies the requirements of the present application and falls within the scope of the present application.

In summary, the present application utilizes an impedance unit to form a plurality of internal impedances and utilizes a preamplifier to cancel a true plurality of external impedances between the transmitting and receiving electrodes. In addition, the present application utilizes a duplexer (and logic control circuit) to select an output signal with similar channel characteristics/noise characteristics, and uses a programmable gain amplifier to eliminate common mode noise and amplify the touch signal to improve the signal to noise ratio.

The above description is only a part of the embodiments of the present application, and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the scope of the present invention. within.

Claims

A capacitance detecting circuit is coupled to the plurality of transmitting electrodes and the plurality of receiving electrodes, wherein the capacitance detecting circuit comprises:

a driving circuit coupled to the plurality of transmitting electrodes for generating a driving signal to the plurality of transmitting electrodes, wherein the plurality of transmitting electrodes and the plurality of receiving electrodes have a plurality of external impedances;

An impedance unit coupled to the driving circuit for receiving the driving signal and generating a plurality of virtual electrode signals, wherein the impedance unit is formed with a plurality of internal impedances, and the plurality of virtual electrode signals are related to Describe a plurality of internal impedances;

a plurality of first amplifiers, each of the first amplifiers having a first input end and a second input end, the first input end of the plurality of first amplifiers being coupled to the plurality of receiving electrodes, The second input end of the plurality of first amplifiers is coupled to the impedance unit, and the plurality of first amplifiers generate a plurality of first output signals;

The plurality of first output signals are related to a plurality of capacitance sizes between the plurality of transmitting electrodes and the plurality of receiving electrodes.
The capacitance detecting circuit according to claim 1, wherein said impedance unit comprises:

At least one capacitor;

The at least one resistor is coupled to the at least one capacitor, and the at least one capacitor forms the plurality of internal impedances with the at least one resistor.
The capacitance detecting circuit of claim 2, wherein the impedance unit further comprises:

An adjustment unit coupled to the at least one resistor for adjusting a resistance value of the at least one resistor such that an external impedance of the plurality of external impedances and an impedance of an internal impedance of the plurality of internal impedances The difference is less than a specific value.
The capacitance detecting circuit according to claim 3, wherein said specific value is 0.4 times said external impedance.
The capacitance detecting circuit according to claim 3, wherein said adjusting unit comprises a storage unit, said storage unit stores a plurality of impedance adjustment values, said adjusting unit adjusting said said plurality of impedance adjustment values The resistance value of at least one resistor.
The capacitance detecting circuit of claim 5, further comprising a control logic circuit coupled to said memory unit, said control logic circuit being controlled by a control unit for outputting said plurality of impedance adjustment values .
The capacitance detecting circuit according to claim 5, wherein said memory unit is a nonvolatile memory.
The capacitance detecting circuit according to claim 5, wherein said memory unit is a volatile memory.
The capacitance detecting circuit of claim 1 further comprising:

The at least one second amplifier is coupled to the plurality of first amplifiers for canceling a common mode noise received by the plurality of transmitting electrodes to generate at least one second output signal;

The at least one second output signal is related to the plurality of capacitor sizes between the plurality of transmitting electrodes and the plurality of receiving electrodes.
The capacitance detecting circuit of claim 9, wherein said at least one second amplifier is a programmable gain amplifier.
The capacitance detecting circuit according to claim 9, wherein the method further comprises:

A duplexer coupled between the plurality of first amplifiers and the at least one second amplifier.
The capacitance detecting circuit according to claim 11, wherein the method further comprises:

a control logic circuit coupled to the reworker, the control logic circuit being controlled by a control unit for controlling the reworker to convert a portion of the first output signals of the plurality of first output signals Passed to the input of the at least one second amplifier.
The capacitance detecting circuit according to claim 1, wherein said driving signal is an alternating current signal.
An electronic device, including

Multiple transfer electrodes;

Multiple receiving electrodes;

A capacitance detecting circuit, the capacitance detecting circuit being the capacitance detecting circuit according to any one of claims 1-13.