CN115562513A

CN115562513A - Capacitive touch sensor and capacitive touch sensing method

Info

Publication number: CN115562513A
Application number: CN202111119635.XA
Authority: CN
Inventors: 光宇; 许有津
Original assignee: Raydium Semiconductor Corp
Current assignee: Raydium Semiconductor Corp
Priority date: 2021-07-01
Filing date: 2021-09-24
Publication date: 2023-01-03
Also published as: TW202303372A; TWI768996B

Abstract

The invention discloses a capacitive touch sensor and a capacitive touch sensing method, which are used for eliminating noise caused by a display screen. The capacitive touch sensing method comprises the following steps: (a) Dividing noise caused by a display screen during the charge transfer; and (b) alternating current coupling the divided noise to the positive input end of the charge amplifier to eliminate common mode noise and improve the signal-to-noise ratio of capacitive touch sensing.

Description

Capacitive touch sensor and capacitive touch sensing method

Technical Field

The present invention relates to capacitive touch sensing, and more particularly, to a capacitive touch sensor with noise cancellation and a capacitive touch sensing method.

Background

As shown in fig. 1 and fig. 2, fig. 1 and fig. 2 are schematic diagrams of a Self-capacitance (Self-capacitance) touch panel TP and a Self-capacitance touch sensing circuit 2 thereof, respectively, of a conventional display screen that is externally mounted or embedded in an Active Matrix Organic Light Emitting Diode (AMOLED). As shown in fig. 1 and fig. 2, the noise NO from the cathode of the AMOLED display screen is coupled to the negative input terminal of the Charge amplifier (Charge amplifier) CAMP through the parasitic capacitor Cb, thereby seriously affecting the signal-to-noise ratio of the self-capacitance touch sensing circuit 2 for self-capacitance touch sensing.

As shown in fig. 3 and 4, fig. 3 and 4 are schematic diagrams of a conventional Mutual-capacitance (Mutual-capacitance) touch panel TP and a Mutual-capacitance touch sensing circuit 4 thereof, which are externally attached to or embedded in an Active Matrix Organic Light Emitting Diode (AMOLED) display screen. As shown in fig. 3 and 4, the noise NO from the cathode of the AMOLED display screen is coupled to the negative input terminal of the Charge amplifier (Charge amplifier) CAMP through the parasitic capacitor Cb, thereby seriously affecting the signal-to-noise ratio of the mutual capacitance touch sensing circuit 4 for performing the mutual capacitance touch sensing.

As can be seen from the above, the conventional capacitive touch sensing circuit externally connected to or embedded in the Active Matrix Organic Light Emitting Diode (AMOLED) display screen is easily affected by noise caused by the AMOLED display screen, especially noise from the Cathode (Cathode) of the AMOLED display screen, so that the signal-to-noise ratio (SNR) of the capacitive touch sensing circuit is not good, and improvement is needed.

Disclosure of Invention

In view of the above, the present invention provides a capacitive touch sensor with noise cancellation function and a capacitive touch sensing method, so as to solve the aforementioned problems encountered in the prior art.

One embodiment of the present invention includes self-capacitive touch sensing circuits, systems, devices, and components.

Another embodiment of the invention includes mutual capacitance touch sensing circuits, systems, devices, and elements.

Still another embodiment of the present invention includes capacitive touch sensing circuits, systems, devices and components embedded in an AMOLED display screen.

Still another embodiment of the present invention includes capacitive touch sensing circuits, systems, devices and components integrated with AMOLED display driver circuits.

An embodiment of the invention is a capacitive touch sensing method. In this embodiment, the capacitive touch sensing method is used to eliminate noise caused by the display screen. The capacitive touch sensing method comprises the following steps: (a) Dividing the noise caused by the display screen during the charge transfer; and (b) alternating current coupling the divided noise to the positive input end of the charge amplifier to eliminate common mode noise and improve the signal-to-noise ratio of capacitive touch sensing.

Another embodiment of the present invention is a capacitive touch sensor. In this embodiment, the capacitive touch sensor is used to eliminate noise caused by the display screen. The capacitive touch sensor includes a charge amplifier and a noise cancellation circuit. The noise elimination circuit comprises an input end, an output end, a first resistor, a second resistor and a capacitor, wherein the first resistor and the second resistor are connected between the input end and the grounding end in series, one end of the capacitor is coupled to the output end, and the other end of the capacitor is coupled between the first resistor and the second resistor. During the charging period, the touch pad on the panel is charged to the working voltage or the grounding voltage, the positive input terminal of the charge amplifier is coupled to the reference voltage through the first switch, the positive input terminal of the charge amplifier is coupled to the output terminal of the noise cancellation circuit, and the input terminal of the noise cancellation circuit is coupled to the first pole of the panel. During the charge transfer, coupling a touch pad on the panel to a negative input terminal of the charge amplifier through a second switch, disconnecting a first switch coupling a positive input terminal of the charge amplifier to a reference voltage, so that the positive input terminal of the charge amplifier is in a floating state, the positive input terminal of the charge amplifier is coupled to an output terminal of the noise cancellation circuit, and an input terminal of the noise cancellation circuit is coupled to a first pole of the panel; and during the charge transfer, the noise elimination circuit divides the voltage of the noise of the first pole of the panel by the first resistor and the second resistor and then performs alternating current coupling to the positive input end of the charge amplifier in a floating state, so that the voltage of the positive input end of the charge amplifier is changed along with the noise of the first pole of the panel, common mode noise generated by the fact that the noise of the first pole of the panel is coupled to the negative input end of the charge amplifier through the parasitic capacitor is eliminated, the signal-to-noise ratio of capacitive touch sensing is improved, and the resistance value proportion of the first resistor and the second resistor is equal to or approximate to the capacitance value proportion of a feedback capacitor and the parasitic capacitor which are coupled with the charge amplifier.

In one embodiment, the first electrode of the panel is a cathode or an anode.

In one embodiment, the first resistor and the second resistor in the noise cancellation circuit are replaced by a first capacitor and a second capacitor, the capacitor in the noise cancellation circuit is removed to directly couple the junction between the first capacitor and the second capacitor as the output terminal of the noise cancellation circuit to the positive input terminal of the charge amplifier, and the capacitance ratio of the first capacitor to the second capacitor is equal to or similar to the capacitance ratio of the parasitic capacitor to the feedback capacitor coupled to the charge amplifier.

In one embodiment, a junction between the first resistor and the second resistor in the noise cancellation circuit is coupled to an input terminal of the analog buffer, and an output terminal of the analog buffer is coupled to one end of the capacitor.

In an embodiment, a junction between a first resistor and a second resistor in the noise cancellation circuit is coupled to one end of a plurality of capacitors, the other ends of the capacitors are respectively coupled to positive input ends of a plurality of charge amplifiers, the noise cancellation circuit generates a voltage division by using the first resistor and the second resistor, and then the voltage division is ac-coupled to the positive input ends of the plurality of charge amplifiers in a floating state through the capacitors, so that voltages of the positive input ends of the plurality of charge amplifiers are respectively changed along with noise of a first pole of a panel, common mode noise generated when the noise of the first pole of the panel is respectively coupled to negative input ends of the plurality of charge amplifiers through a plurality of parasitic capacitors is eliminated, and a signal-to-noise ratio of capacitive touch sensing is improved.

In one embodiment, a junction between the first resistor and the second resistor in the noise cancellation circuit is coupled to an input terminal of the analog buffer, and an output terminal of the analog buffer is coupled to one terminal of the plurality of capacitors.

In one embodiment, the first resistor and the second resistor in the noise cancellation circuit are replaced by a first capacitor and a second capacitor, and the capacitance ratio of the first capacitor and the second capacitor is equal to or similar to the capacitance ratio of the parasitic capacitor and the feedback capacitor coupled to the charge amplifier.

Another embodiment of the present invention is a capacitive touch sensor. In this embodiment, the capacitive touch sensor is used to eliminate noise caused by the display screen. The capacitive touch sensor includes a driving circuit and a capacitive sensing circuit. The capacitance sensing circuit is coupled to the driving circuit. The capacitance sensing circuit includes a charge amplifier and a noise cancellation circuit. The noise elimination circuit comprises an input end, an output end, a first resistor, a second resistor and a capacitor, wherein the first resistor and the second resistor are connected between the input end and the grounding end in series, one end of the capacitor is coupled to the output end, and the other end of the capacitor is coupled between the first resistor and the second resistor. During the charging period, at least one touch driving channel on the panel is charged to a working voltage or a ground voltage and a touch sensing channel on the panel is charged to a reference voltage, a positive input terminal of the charge amplifier is coupled to the reference voltage through a first switch, the positive input terminal of the charge amplifier is simultaneously coupled to an output terminal of the noise cancellation circuit, and an input terminal of the noise cancellation circuit is coupled to a first pole of the panel. During the charge transfer period, charging the touch driving channel to a working voltage or a grounding voltage, simultaneously coupling the touch sensing channel to the negative input end of the charge amplifier, and disconnecting the first switch which couples the positive input end of the charge amplifier to a reference voltage to enable the positive input end of the charge amplifier to be in a floating state; and during the charge transfer, the noise elimination circuit divides the voltage of the noise of the first pole of the panel through the first resistor and the second resistor and then carries out alternating current coupling to the positive input end of the charge amplifier in a floating state, so that the voltage of the positive input end of the charge amplifier is changed along with the noise of the first pole of the panel, common mode noise generated by the fact that the noise of the first pole of the panel is coupled to the negative input end of the charge amplifier through the parasitic capacitor is eliminated, the signal to noise ratio of capacitive touch sensing is improved, and the resistance value proportion of the first resistor and the second resistor is equal to or approximate to the capacitance value proportion of a feedback capacitor and the parasitic capacitor which are coupled with the charge amplifier.

In one embodiment, the first electrode of the panel is a cathode or an anode.

In an embodiment, the first resistor and the second resistor of the noise cancellation circuit are replaced by a first capacitor and a second capacitor, the capacitor of the noise cancellation circuit is removed to directly couple the junction between the first capacitor and the second capacitor to the positive input terminal of the charge amplifier as the output terminal of the noise cancellation circuit, and the capacitance ratio of the first capacitor to the second capacitor is equal to or similar to the capacitance ratio of the parasitic capacitor to the feedback capacitor.

In one embodiment, a junction between the first resistor and the second resistor in the noise cancellation circuit is coupled to an input terminal of the analog buffer, and an output terminal of the analog buffer is coupled to one terminal of the capacitor.

In one embodiment, the first resistor and the second resistor in the noise cancellation circuit are replaced by a first capacitor and a second capacitor.

Another embodiment according to the present invention is a capacitive touch sensor. In this embodiment, the capacitive touch sensor is used to eliminate noise caused by the display screen. The capacitive touch sensor includes a driving circuit and a capacitive sensing circuit. The capacitance sensing circuit is coupled to the driving circuit. The capacitance sensing circuit includes a charge amplifier, an output analog buffer and a noise cancellation circuit. The noise elimination circuit comprises a first input end, a first output end, a first resistor, a second resistor, a first capacitor, a second input end, a second output end, a third resistor, a fourth resistor and a second capacitor, wherein the first resistor and the second resistor are connected between the first input end and the grounding end in series; during the charging period, charging at least one touch driving channel on the panel to a first driving voltage and charging a touch sensing channel on the panel to a reference voltage, wherein a positive input terminal of a charge amplifier is coupled to the reference voltage through a first switch, the positive input terminal of the charge amplifier is simultaneously coupled to a first output terminal of a noise cancellation circuit, and a first input terminal of the noise cancellation circuit is coupled to a first pole of the panel; during the charging period, the positive input end of the output analog buffer of the driving voltage source of the driving channel is also coupled to the driving reference voltage through the second switch, and the positive input end of the output analog buffer is also coupled to the second output end of the noise elimination circuit; during the charge transfer, coupling the touch driving channel to the second driving voltage through the third switch, coupling the touch sensing channel to the negative input terminal of the charge amplifier, and disconnecting the first switch coupling the positive input terminal of the charge amplifier to the reference voltage, so that the positive input terminal of the charge amplifier is in a floating state, the positive input terminal of the charge amplifier is coupled to the first output terminal of the noise cancellation circuit, and the first input terminal of the noise cancellation circuit is coupled to the first pole of the panel; during the charge transfer period, the second switch which also couples the positive input end of the output analog buffer to the driving reference voltage is opened, so that the positive input end of the output analog buffer is in a floating state, the positive input end of the output analog buffer is coupled to the second output end of the noise elimination circuit, and the second input end of the noise elimination circuit is coupled to the first pole of the panel; during the charge transfer period, the noise elimination circuit divides the voltage of the noise of the first pole of the panel through the first resistor and the second resistor and then carries out alternating current coupling to the positive input end of the charge amplifier in a floating state, so that the voltage of the positive input end of the charge amplifier is changed along with the noise of the first pole of the panel, common mode noise generated when the noise of the first pole of the panel is coupled to the negative input end of the charge amplifier through the parasitic capacitor is eliminated, and the signal-to-noise ratio of capacitive touch sensing is improved; during the charge transfer period, the noise cancellation circuit ac-couples the noise of the first electrode of the panel to the positive input terminal of the output analog buffer in a floating state after dividing the voltage by the third resistor and the fourth resistor, so that the voltage of the positive input terminal of the output analog buffer changes with the noise of the first electrode of the panel, thereby canceling the common mode noise generated when the noise of the first electrode of the panel is coupled to the negative input terminal of the charge amplifier via the parasitic capacitor, and increasing the signal-to-noise ratio of the capacitive touch sensing.

In one embodiment, the first electrode of the panel is a cathode or an anode.

In an embodiment, a junction between a first resistor and a second resistor in the noise cancellation circuit is coupled to one end of a plurality of first capacitors and one end of a second capacitor, the other end of the plurality of first capacitors are respectively coupled to positive input ends of a plurality of charge amplifiers, the noise cancellation circuit generates voltage division by using the first resistors and the second resistors, and then the voltage division is respectively ac-coupled to the positive input ends of the plurality of charge amplifiers and the positive input end of the output analog buffer in a floating state through the plurality of first capacitors and the second capacitors, so that voltages of the positive input ends of the plurality of charge amplifiers and the positive input end of the output analog buffer are respectively changed along with noise of a first pole of a panel, and the second driving voltage and the voltages of the positive input ends of the plurality of charge amplifiers are simultaneously jittered to cancel the noise.

In an embodiment, the noise levels of the voltages at the positive input terminals of the charge amplifiers are adjusted by separately adjusting the resistance ratio of the first resistor to the second resistor in the noise cancellation circuit, and the noise level of the second driving voltage is adjusted by separately adjusting the resistance ratio of the third resistor to the fourth resistor in the noise cancellation circuit, so as to optimize the noise cancellation effect.

Compared with the prior art, the capacitive touch sensor and the capacitive touch sensing method of the invention utilize the charge amplifier to perform alternating current coupling on the noise of the cathode or the anode of the AMOLED display screen to the positive input end of the charge amplifier after the voltage division through the resistor or the capacitor during the charge transfer period, so as to achieve the specific effects of eliminating the common mode noise and improving the signal-to-noise ratio of the capacitive touch sensing.

The advantages and spirit of the present invention will be further understood by the following detailed description of the invention and the accompanying drawings.

Drawings

Fig. 1 and 2 are schematic diagrams of a conventional self-capacitance touch panel and a self-capacitance touch sensing circuit thereof externally attached to or embedded in an AMOLED display screen.

Fig. 3 and 4 are schematic diagrams of a mutual capacitance touch panel and a mutual capacitance touch sensing circuit thereof, respectively, which are externally attached to or embedded in an AMOLED display screen.

Fig. 5 is a schematic diagram of a self-capacitance touch sensing circuit of a capacitive touch sensor during a charging period and a transferring period according to an embodiment of the invention.

Fig. 6 to 9 are schematic diagrams of different embodiments of a noise cancellation circuit in a capacitive touch sensor, respectively.

Fig. 10 is a schematic diagram of a noise cancellation circuit including a self-capacitance touch sensing circuit having a plurality of capacitors respectively coupled to a plurality of charge amplifiers.

Fig. 11 is a schematic diagram of a self-capacitance touch sensing circuit of a capacitive touch sensor during a charging period and a transferring period according to another embodiment of the invention.

Fig. 12 is a schematic diagram of a mutual capacitance touch sensing circuit of a capacitive touch sensor during a charging period and a transferring period in another embodiment of the invention.

Fig. 13 is a schematic diagram of a mutual capacitance touch sensing circuit in which a noise cancellation circuit includes a plurality of capacitors respectively coupled to a plurality of charge amplifiers.

Fig. 14 is a schematic diagram of a mutual capacitance touch sensing circuit of a capacitive touch sensor during a charging period and a transferring period according to another embodiment of the invention.

Fig. 15 is a schematic diagram of a mutual capacitance touch sensing circuit of a capacitive touch sensor during a charging period and a transferring period in another embodiment of the invention.

Fig. 16A and 16B are schematic diagrams of a mutual capacitance touch sensing circuit in which the noise cancellation circuit includes a plurality of first capacitors respectively coupled to a plurality of charge amplifiers and a second capacitor coupled to an output analog buffer.

Fig. 17A and 17B are schematic diagrams of a mutual capacitance touch sensing circuit in which a noise cancellation circuit includes a plurality of capacitors respectively coupled to a plurality of charge amplifiers.

Fig. 18 is a flowchart of a capacitive touch sensing method according to another embodiment of the invention.

Description of the main element symbols:

self-capacitance touch sensing circuit

Self-capacitance touch panel

Pad

A capacitance sensing circuit

Mutual capacitance touch sensing circuit

TS

Cathode for CAT

Noise no

CAMP

Reference voltage

Output voltage

Parasitic capacitance

Feedback capacitor

DRC

TX 1-TX8

RX 1-rx8

Mutual capacitance

Touch drive channel

Touch sensing channel

Operating voltage of VDD

Touch pad

5. 10-17

Noise cancellation circuit

First resistance

R2

Capacitor

Front input end

Negative input

Voltage of VCM

C1

C2

ABF

Capacitance of Cnc 1-CncN

Touch pad

Cb 1-CbN

Feedback capacitor Cf 1-CfN

CAMP 1-CAMPN

Organic light emitting diode

Anode of no

Touch driving channel from CHTX1 to CHTXN

CHRX 1-CHRXN

Output analog buffer for OABF

R1tx

R2tx

First noise cancellation circuit

Second noise cancellation circuit

Capacitor Cctcx

Voltage vcmtx

Vreftx

A first driving voltage

A second driving voltage

W1-W2

WA-WF

S10-S12

Detailed Description

The term "coupled", as used throughout the specification of the present invention, may refer to any direct or indirect connection means. For example, if a first device couples to a second device, that connection may be through a direct connection, or through an indirect connection via other devices and some means of connection.

One embodiment according to the present invention is a capacitive touch sensor. In this embodiment, the capacitive touch sensor can be applied to an AMOLED display screen for eliminating noise caused by the AMOLED display screen, and the capacitive touch sensor can be a self-capacitive touch sensing circuit or a mutual-capacitive touch sensing circuit, but not limited thereto.

As shown in fig. 5, fig. 5 is a schematic diagram of the capacitive touch sensor in the embodiment during a charging period and a transferring period. As shown in fig. 5, the capacitive touch sensor 5 is a self-capacitive touch sensor, which includes a charge amplifier CAMP and a noise cancellation circuit NCC. The noise cancellation circuit NCC includes a first resistor R1, a second resistor R2, and a capacitor Cnc. The first resistor R1 and the second resistor R2 are connected in series between the cathode CAT of the AMOLED display screen and the ground terminal. The capacitor Cnc has one end coupled to the positive input terminal + of the charge amplifier CAMP and the other end coupled between the first resistor R1 and the second resistor R2.

During the charging period, the touch pad on the panel is charged to the working voltage VDD or the ground voltage (GND), the positive input terminal + of the charge amplifier CAMP is coupled to the reference voltage VREF through the switch W1, the positive input terminal + of the charge amplifier CAMP is coupled to the output terminal of the noise cancellation circuit NCC, and the input terminal of the noise cancellation circuit NCC is coupled to the cathode CAT of the AMOLED display screen.

During the charge transfer, the touch pad on the panel is coupled to the negative input terminal of the charge amplifier CAMP through the switch WE, and the positive input terminal of the charge amplifier CAMP + the switch W1 coupled to the reference voltage VREF is turned off, so that the positive input terminal + of the charge amplifier CAMP is in a floating state. The positive input + of the charge amplifier CAMP is coupled to the output of the noise cancellation circuit NCC. The input of the noise cancellation circuit NCC is coupled to the cathode CAT.

During the charge transfer, the noise cancellation circuit NCC ac couples the noise NO of the cathode CAT to the positive input terminal + of the floating charge amplifier CAMP after dividing the voltage across the first resistor R1 and the second resistor R2, so that the voltage VCM at the positive input terminal + of the charge amplifier CAMP is varied with the noise NO of the cathode CAT, thereby canceling the Common-mode noise (Common-mode noise) generated when the noise NO of the cathode CAT is coupled to the negative input terminal of the charge amplifier CAMP through the parasitic capacitor Cb, thereby improving the signal-to-noise ratio of the capacitive touch sensor 5 for capacitive touch sensing.

It should be noted that the ratio of the resistance values of the first resistor R1 and the second resistor R2 is equal to or similar to the ratio of the capacitance values of the feedback capacitor Cf and the parasitic capacitor Cb coupled to the charge amplifier CAMP. The reference voltage VREF may be the operating voltage VDD or the ground voltage (GND) or any voltage.

In an embodiment, the first resistor R1 and the second resistor R2 of the noise cancellation circuit NCC in fig. 5 can be replaced by the first capacitor C1 and the second capacitor C2 in fig. 6, but not limited thereto.

In an embodiment, the first resistor R1 and the second resistor R2 of the noise cancellation circuit NCC in fig. 5 can be replaced by the first capacitor C1 and the second capacitor C2 in fig. 7. As shown in fig. 7, the capacitor Cnc in the noise cancellation circuit NCC is removed and the junction of the first capacitor C1 and the second capacitor C2 is directly coupled to the positive input terminal of the charge amplifier CAMP as the output terminal of the noise cancellation circuit NCC. The capacitance ratio of the first capacitor C1 and the second capacitor C2 is equal to or similar to the capacitance ratio of the parasitic capacitor Cb and the feedback capacitor Cf, but not limited thereto.

In one embodiment, as shown in fig. 8, the junction between the first resistor R1 and the second resistor R2 in the noise cancellation circuit NCC is coupled to the positive input terminal of the analog buffer ABF, and the output terminal of the analog buffer ABF is coupled to one terminal of the capacitor cn c and the negative input terminal-of the analog buffer ABF, but not limited thereto.

In an embodiment, the first resistor R1 and the second resistor R2 of the noise cancellation circuit NCC in fig. 8 can be replaced by the first capacitor C1 and the second capacitor C2 in fig. 9, but not limited thereto.

In one embodiment, as shown in fig. 10, the junctions between the first resistor R1 and the second resistor R2 in the noise cancellation circuit NCC are respectively coupled to one end of the capacitors Cnc1 to CncN. The other ends of the capacitors Cnc1 to CncN are respectively coupled to the positive input ends + of the charge amplifiers CAMP1 to CAMP. The noise cancellation circuit NCC generates a voltage division by using the first resistor R1 and the second resistor R2, and ac couples the divided voltage to the positive input terminals of the plurality of charge amplifiers CAMP1 to CAMP in a floating state through the plurality of capacitors Cnc1 to CncN, so that the voltages VCM of the positive input terminals of the plurality of charge amplifiers CAMP1 to CAMP + respectively vary with the noise NO of the cathode CAT, and the noise NO of the cathode CAT is coupled to the negative input terminals of the plurality of charge amplifiers CAMP1 to CAMP through the plurality of parasitic capacitors Cb1 to CbN, thereby eliminating a common mode noise generated when the noise NO of the cathode CAT is coupled to the negative input terminals of the plurality of charge amplifiers CAMP1 to CAMP, and thus improving the signal-to-noise ratio of capacitive touch sensing.

In an embodiment, the first resistor R1 and the second resistor R2 in the noise cancellation circuit NCC in fig. 10 may also be coupled to the positive input terminal of the analog buffer ABF as shown in fig. 8, the output terminal of the analog buffer ABF is coupled to one terminal of the capacitors Cnc1 to CncN and the negative input terminal of the analog buffer ABF, and the first resistor R1 and the second resistor R2 may also be replaced by the first capacitor C1 and the second capacitor C2 in fig. 9, but not limited thereto.

It should be noted that, although the cathode CAT of the AMOLED display screen is taken as an example in the above embodiments, the input terminal of the noise cancellation circuit NCC may also be coupled to the anode ANO of the AMOLED display screen, as shown in fig. 11, but not limited thereto.

As shown in fig. 12, in another embodiment, the capacitive touch sensor 12 is a mutual capacitive touch sensor, which includes a driving circuit and a capacitive sensing circuit. The capacitance sensing circuit includes a charge amplifier CAMP and a noise cancellation circuit NCC. The noise cancellation circuit NCC includes a first resistor R1, a second resistor R2, and a capacitor Cnc. The first resistor R1 and the second resistor R2 are connected in series between the cathode CAT of the AMOLED display screen and the ground terminal, one end of the capacitor Cnc is coupled to the positive input terminal + of the charge amplifier CAMP, and the other end is coupled between the first resistor R1 and the second resistor R2.

During the charging, at least one touch driving channel CHTX on the panel is charged to the operating voltage VDD or the ground voltage (GND) and a touch sensing channel CHRX on the panel is charged to the reference voltage VREF. The positive input + of the charge amplifier CAMP is coupled to the reference voltage VREF via the switch W1. The positive input + of the charge amplifier CAMP is simultaneously coupled to the output of the noise cancellation circuit NCC. The input of the noise cancellation circuit NCC is coupled to the cathode CAT.

During the charge transfer, the touch driving channel CHTX is charged to the working voltage VDD or the ground voltage (GND), and the touch sensing channel CHRX is coupled to the negative input terminal of the charge amplifier CAMP, and the positive input terminal of the charge amplifier CAMP + the switch W1 coupled to the reference voltage VREF is turned off, so that the positive input terminal + of the charge amplifier CAMP is in a floating state. The positive input + of the charge amplifier CAMP is coupled to the output of the noise cancellation circuit NCC. The input of the noise cancellation circuit NCC is coupled to the cathode CAT.

During the charge transfer, the noise cancellation circuit NCC divides the voltage of the noise NO of the cathode CAT by the first resistor R1 and the second resistor R2 and then ac couples the divided voltage to the positive input terminal of the floating charge amplifier CAMP, so that the voltage VCM of the positive input terminal + of the charge amplifier CAMP is changed with the noise NO of the cathode CAT, thereby canceling the common mode noise generated when the noise NO of the cathode CAT is coupled to the negative input terminal of the charge amplifier CAMP through the parasitic capacitor Cb, and thus the signal-to-noise ratio of the capacitive touch sensing can be improved. The ratio of the resistance values of the first resistor R1 and the second resistor R2 is equal to or similar to the ratio of the capacitance values of the feedback capacitor Cf coupled to the charge amplifier CAMP and the parasitic capacitor Cb.

In practical applications, the first resistor R1 and the second resistor R2 of the noise cancellation circuit NCC are coupled to the input terminal of the analog buffer ABF, and the output terminal of the analog buffer ABF is coupled to one end of the capacitor Cnc; the first resistor R1 and the second resistor R2 in the noise cancellation circuit NCC may be replaced by a first capacitor C1 and a second capacitor C2, and the capacitor Cnc in the noise cancellation circuit NCC may be removed to directly couple the junction between the first capacitor C1 and the second capacitor C2 as the output terminal of the noise cancellation circuit NCC to the positive input terminal of the charge amplifier CAMP +; the capacitance ratio of the first capacitor C1 and the second capacitor C2 is equal to or similar to the capacitance ratio of the parasitic capacitor Cb and the feedback capacitor Cf, but not limited thereto.

In an embodiment, as shown in fig. 13, a contact point between the first resistor R1 and the second resistor R2 in the noise cancellation circuit NCC is coupled to one end of the capacitors Cnc1 to CncN, the other ends of the capacitors Cnc1 to CncN are coupled to positive input terminals of the charge amplifiers CAMP1 to CAMP respectively, and the noise cancellation circuit NCC generates a voltage division by using the first resistor R1 and the second resistor R2, and then ac-couples the voltage division to the positive input terminals of the charge amplifiers CAMP1 to CAMP in a floating state through the capacitors Cnc1 to CncN, so that the voltage VCM of the positive input terminals of the charge amplifiers CAMP1 to CAMP respectively varies with CAT noise NO of the cathode CAT, so as to cancel the touch noise generated by the noise NO of the cathode CAT being coupled to the negative input terminals of the charge amplifiers CAMP1 to CAMP through the parasitic capacitors Cb1 to bccn respectively, thereby improving the signal-to-noise ratio of the capacitance sensing.

It should be noted that, although the cathode CAT of the AMOLED display screen is taken as an example in the above embodiments, the input terminal of the noise cancellation circuit NCC may also be coupled to the anode ANO of the AMOLED display screen, as shown in fig. 14, but not limited thereto.

As shown in fig. 15, in another embodiment, the capacitive touch sensor 15 is a mutual capacitive touch sensor, which includes a driving circuit and a capacitive sensing circuit for simultaneously eliminating noise introduced by the parasitic capacitance Cb of the touch driving channel CHTX and the touch sensing channel CHRX. The capacitance sensing circuit includes a charge amplifier CAMP, an output analog buffer OABF, and a noise cancellation circuit NCC. The noise cancellation circuit NCC includes a first noise cancellation circuit NCC _ RX and a second noise cancellation circuit NCC _ TX. The first noise cancellation circuit NCC _ RX includes a first input terminal, a first output terminal, a first resistor R1, a second resistor R2, and a first capacitor cn. The second noise cancellation circuit NCC _ TX includes a second input terminal, a second output terminal, a third resistor R1TX, a fourth resistor R2TX, and a second capacitor Cnctx. The first resistor R1 and the second resistor R2 are connected in series between the first input terminal of the first noise cancellation circuit NCC _ RX and the ground terminal, the cathode CAT of the AMOLED display screen is coupled to the first input terminal of the first noise cancellation circuit NCC _ RX, one end of the first capacitor Cnc is a first output terminal of the first noise cancellation circuit NCC _ RX, and is coupled to the positive input terminal + of the charge amplifier CAMP, and the other end is coupled between the first resistor R1 and the second resistor R2. The third resistor R1TX and the fourth resistor R2TX are connected in series between the second input terminal of the second noise cancellation circuit NCC _ TX and the ground terminal, the cathode CAT of the AMOLED display screen is coupled to the second input terminal of the second noise cancellation circuit NCC _ TX, one end of the second capacitor Cnctx is the second output terminal of the second noise cancellation circuit NCC _ TX, which is coupled to the positive input terminal + of the output analog buffer OABF, and the other end is coupled between the third resistor R1TX and the fourth resistor R2TX.

During the charging, at least one touch driving channel CHTX on the panel is charged to the first driving voltage VFF and the touch sensing channel CHRX on the panel is charged to the reference voltage VREF. The positive input + of the charge amplifier CAMP is coupled to the reference voltage VREF via the switch W1. A positive input terminal + of the charge amplifier CAMP is simultaneously coupled to the first output terminal of the first noise cancellation circuit NCC _ RX. A first input of the first noise cancellation circuit NCC _ RX is coupled to the cathode CAT.

During charging, the positive input terminal + of the output analog buffer OABF is also coupled to the driving reference voltage VREFtx via the switch W2, and is also coupled to the second output terminal of the second noise cancellation circuit NCC _ TX.

During the charge transfer, the touch driving channel CHTX is coupled to a second driving voltage VEE via the switch WA, the second driving voltage VEE is an output voltage of the output analog buffer OABF, the touch sensing channel CHRX is coupled to the negative input terminal of the charge amplifier CAMP, the positive input terminal of the charge amplifier CAMP + the switch W1 coupled to the reference voltage VREF is disconnected, the positive input terminal + of the charge amplifier CAMP is in a floating state, the positive input terminal + of the charge amplifier CAMP + is coupled to the first output terminal of the first noise cancellation circuit NCC _ RX, and the first input terminal of the first noise cancellation circuit NCC is coupled to the cathode CAT.

During the charge transfer, the positive input terminal + of the output analog buffer OABF is also coupled to the switch W2 of the driving reference voltage VREFtx in an open circuit, so that the positive input terminal + of the output analog buffer OABF is in a floating state, the positive input terminal + of the output analog buffer OABF is coupled to the second output terminal of the second noise cancellation circuit NCC _ TX, the second input terminal of the second noise cancellation circuit NCC _ TX is coupled to the cathode CAT, and the second driving voltage VEE of the output analog buffer OABF is varied with the noise NO of the cathode CAT.

During the charge transfer, the first noise cancellation circuit NCC _ RX ac couples the noise NO of the cathode CAT to the positive input terminal of the floating charge amplifier CAMP + after dividing the voltage across the first resistor R1 and the second resistor R2, so that the voltage VCM at the positive input terminal of the charge amplifier CAMP + varies with the noise NO of the cathode CAT to cancel the common mode noise generated when the noise NO of the cathode CAT is coupled to the negative input terminal of the charge amplifier CAMP through the parasitic capacitor Cb, thereby improving the signal-to-noise ratio of the capacitive touch sensing.

During the charge transfer, the second noise cancellation circuit NCC _ TX divides the voltage of the noise NO of the cathode CAT by the third resistor R1TX and the fourth resistor R2TX and then ac couples the divided voltage to the positive input terminal of the floating output analog buffer OABF, so that the voltage VCMTX of the positive input terminal + of the output analog buffer OABF varies with the noise NO of the cathode CAT, thereby canceling the common mode noise generated when the noise NO of the cathode CAT is coupled to the negative input terminal of the charge amplifier CAMP through the parasitic capacitor Cb, and thus improving the signal-to-noise ratio of the capacitive touch sensing.

In practical applications, the first driving voltage VFF and the second driving voltage VEE have different potentials; the resistance ratio of the first resistor R1 and the second resistor R2 is equal to or similar to the capacitance ratio of the feedback capacitor Cf coupled to the charge amplifier CAMP and the parasitic capacitor Cb; the resistance ratio of the third resistor R1tx to the fourth resistor R2tx is equal to or similar to the capacitance ratio of the feedback capacitor Cf coupled to the charge amplifier CAMP and the parasitic capacitor Cb.

In one embodiment, as shown in fig. 16A and 16B, the capacitive touch sensor 16 is a mutual capacitive touch sensor for simultaneously eliminating noise introduced by the plurality of parasitic capacitances Cb1 to CbN of the plurality of touch driving channels CHTX1 to CHTXN and the plurality of touch sensing channels CHRX1 to CHRXN. The first resistor R1 and the second resistor R2 of the noise cancellation circuit NCC are coupled to one end of the first capacitors Cnc1 to CncN and the second capacitor Cnctx. The other ends of the first capacitors Cnc1 to CncN are respectively coupled to the positive input ends + of the charge amplifiers CAMP1 to CAMP. The noise cancellation circuit NCC generates a voltage division by using the first resistor R1 and the second resistor R2, and ac-couples the divided voltages to the positive input terminals + of the plurality of charge amplifiers CAMP1 to CAMP1 in a floating state and the positive input terminal + of the output analog buffer OABF through the plurality of first capacitors Cnc1 to CncN and the second capacitor Cnctx, respectively, so that the voltage VCM at the positive input terminals + of the plurality of charge amplifiers CAMP1 to CAMP1 and the voltage VCMTX at the positive input terminal + of the output analog buffer OABF are respectively changed according to the noise NO of the cathode CAT, and the second driving voltage VEE and the voltage VCM at the positive input terminals + of the plurality of charge amplifiers CAMP1 to CAMP1 are simultaneously dithered to cancel the noise.

In one embodiment, as shown in fig. 17A and 17B, the capacitive touch sensor 17 is a mutual capacitive touch sensor for simultaneously eliminating noise introduced by the parasitic capacitances Cb1 to CbN of the touch driving channels CHTX1 to CHTXN and the touch sensing channels CHRX1 to CHRXN. Since the noise cancellation circuit NCC includes the first noise cancellation circuit NCC _ RX and the second noise cancellation circuit NCC _ TX, which have different impedance voltage-dividing circuits, the noise magnitudes of the voltages at the positive input terminals + of the plurality of charge amplifiers CAMP1 to CAMP may be adjusted by separately adjusting the resistance ratio of the first resistor R1 to the second resistor R2, and the noise magnitude of the second driving voltage VEE may be adjusted by separately adjusting the resistance ratio of the third resistor R1TX to the fourth resistor R2TX, so as to optimize the noise cancellation effect.

Another embodiment of the present invention is a capacitive touch sensing method. In this embodiment, the capacitive touch sensing method is used to eliminate noise caused by the AMOLED screen. As shown in fig. 18, the capacitive touch sensing method includes the following steps:

step S10: dividing the noise caused by the display screen during the charge transfer; and

step S12: and the noise subjected to voltage division is subjected to alternating current coupling to the positive input end of the charge amplifier so as to eliminate common mode noise and improve the signal to noise ratio of capacitive touch sensing.

Claims

1. A capacitive touch sensing method for eliminating noise caused by a display screen, the capacitive touch sensing method comprising:

(a) Dividing the noise caused by the display screen during the charge transfer; and

(b) And the noise subjected to voltage division is subjected to alternating current coupling to the positive input end of the charge amplifier so as to eliminate common mode noise and improve the signal-to-noise ratio of capacitive touch sensing.

2. A capacitive touch sensor for eliminating noise caused by a display screen, the capacitive touch sensor comprising:

a charge amplifier; and

the noise elimination circuit comprises an input end, an output end, a first resistor, a second resistor and a capacitor, wherein the first resistor and the second resistor are connected between the input end and a grounding end in series;

during the charging period, the touch pad on the panel is charged to a working voltage or a grounding voltage, the positive input end of the charge amplifier is coupled to a reference voltage through a first switch, the positive input end of the charge amplifier is coupled to the output end of the noise elimination circuit, and the input end of the noise elimination circuit is coupled to the first pole of the panel;

during the charge transfer, the touch pad on the panel is coupled to the negative input terminal of the charge amplifier through a second switch, the first switch, which couples the positive input terminal of the charge amplifier to the reference voltage, is turned off, so that the positive input terminal of the charge amplifier is in a floating state, the positive input terminal of the charge amplifier is coupled to the output terminal of the noise cancellation circuit, and the input terminal of the noise cancellation circuit is coupled to the first pole of the panel; and

during the charge transfer, the noise cancellation circuit ac-couples the noise of the first electrode of the panel to the positive input terminal of the charge amplifier in a floating state after dividing the voltage across the first resistor and the second resistor, so that the voltage at the positive input terminal of the charge amplifier is changed along with the noise of the first electrode of the panel, thereby canceling the common mode noise generated by coupling the noise of the first electrode of the panel to the negative input terminal of the charge amplifier through the parasitic capacitor, and improving the signal-to-noise ratio of capacitive touch sensing.

3. The capacitive touch sensor of claim 2, wherein the first electrode of the panel is a cathode or an anode.

4. The capacitive touch sensor of claim 3, wherein the first and second resistors of the noise cancellation circuit are replaced with first and second capacitors, and the capacitor of the noise cancellation circuit is removed to directly couple the junction between the first and second capacitors as the output of the noise cancellation circuit to the positive input of the charge amplifier.

5. The capacitive touch sensor of claim 3, wherein a junction between the first resistor and the second resistor of the noise cancellation circuit is coupled to an input of an analog buffer, and an output of the analog buffer is coupled to an end of the capacitor.

6. The capacitive touch sensor according to claim 3, wherein a contact between the first resistor and the second resistor in the noise cancellation circuit is coupled to one end of a plurality of capacitors, the other ends of the plurality of capacitors are coupled to the plurality of output terminals, the plurality of output terminals are coupled to positive input terminals of a plurality of charge amplifiers, the noise cancellation circuit generates a voltage division by the first resistor and the second resistor, and then ac-couples the divided voltage to the positive input terminals of the plurality of charge amplifiers in a floating state through the plurality of capacitors, so that voltages of the positive input terminals of the plurality of charge amplifiers are respectively changed according to the noise of the first pole of the panel, thereby eliminating common mode noise generated by the noise of the first pole of the panel being coupled to negative input terminals of the plurality of charge amplifiers through the plurality of parasitic capacitors, and improving a signal-to-noise ratio of capacitive touch sensing.

7. The capacitive touch sensor of claim 6, wherein a junction between the first resistor and the second resistor of the noise cancellation circuit is coupled to an input of an analog buffer, and an output of the analog buffer is coupled to one end of the plurality of capacitors.

8. The capacitive touch sensor of any one of claims 3, 5, 6, and 7, wherein the first resistor and the second resistor of the noise cancellation circuit are replaced by a first capacitor and a second capacitor.

9. A capacitive touch sensor for eliminating noise caused by a display screen, the capacitive touch sensor comprising:

the capacitance sensing circuit is coupled to the driving circuit, and includes a charge amplifier and a noise cancellation circuit:

during the charging period, at least one touch driving channel on the panel is charged to a working voltage or a grounding voltage and a touch sensing channel on the panel is charged to a reference voltage, a positive input terminal of the charge amplifier is coupled to the reference voltage through a first switch, a positive input terminal of the charge amplifier is simultaneously coupled to an output terminal of the noise cancellation circuit, and an input terminal of the noise cancellation circuit is coupled to a first pole of the panel;

during the charge transfer period, charging the touch driving channel to the working voltage or the ground voltage, coupling the touch sensing channel to the negative input terminal of the charge amplifier, and disconnecting the first switch coupling the positive input terminal of the charge amplifier to the reference voltage to make the positive input terminal of the charge amplifier in a floating state, wherein the positive input terminal of the charge amplifier is coupled to the output terminal of the noise cancellation circuit, and the input terminal of the noise cancellation circuit is coupled to the first pole of the panel; and

during the charge transfer period, the noise elimination circuit divides the voltage of the noise of the first pole of the panel by the first resistor and the second resistor and then ac couples the divided voltage to the positive input end of the charge amplifier in a floating state, so that the voltage of the positive input end of the charge amplifier is changed along with the noise of the first pole of the panel, common mode noise generated when the noise of the first pole of the panel is coupled to the negative input end of the charge amplifier by a parasitic capacitor is eliminated, and the signal-to-noise ratio of capacitive touch sensing is improved.

10. The capacitive touch sensor of claim 9, wherein the first electrode of the panel is a cathode or an anode.

11. The capacitive touch sensor of claim 10, wherein the first and second resistors of the noise cancellation circuit are replaced with first and second capacitors, and the capacitor of the noise cancellation circuit is removed to directly couple the junction between the first and second capacitors as the output of the noise cancellation circuit to the positive input of the charge amplifier.

12. The capacitive touch sensor of claim 10, wherein a junction between the first resistor and the second resistor of the noise cancellation circuit is coupled to an input of an analog buffer, and an output of the analog buffer is coupled to an end of the capacitor.

13. The capacitive touch sensor according to claim 10, wherein a contact between the first resistor and the second resistor in the noise cancellation circuit is coupled to one end of a plurality of capacitors, the other ends of the plurality of capacitors are coupled to the plurality of output terminals, the output terminals of the noise cancellation circuit are coupled to positive input terminals of a plurality of charge amplifiers, and the noise cancellation circuit generates a voltage division by the first resistor and the second resistor and then ac-couples the divided voltage to the positive input terminals of the plurality of charge amplifiers in a floating state through the plurality of capacitors, so that the voltages of the positive input terminals of the plurality of charge amplifiers are respectively changed according to the noise of the first pole of the panel, thereby eliminating common mode noise generated by the noise of the first pole of the panel being coupled to negative input terminals of the plurality of charge amplifiers through the plurality of parasitic capacitors, and improving a signal-to-noise ratio of capacitive touch sensing.

14. The capacitive touch sensor of claim 10, wherein the first resistor and the second resistor of the noise cancellation circuit are coupled to an input of an analog buffer, and an output of the analog buffer is coupled to one end of the plurality of capacitors.

15. The capacitive touch sensor of any one of claims 10, 12, 13, and 14, wherein the first resistor and the second resistor of the noise cancellation circuit are replaced with a first capacitor and a second capacitor.

16. A capacitive touch sensor for eliminating noise caused by a display screen, the capacitive touch sensor comprising a driving circuit and a capacitive sensing circuit:

the capacitance sensing circuit is coupled to the driving circuit, and includes a charge amplifier, an output analog buffer, and a noise cancellation circuit:

the noise elimination circuit comprises a first input end, a first output end, a first resistor, a second resistor, a first capacitor, a second input end, a second output end, a third resistor, a fourth resistor and a second capacitor, wherein the first resistor and the second resistor are connected between the first input end and a grounding end in series;

during charging, at least one touch driving channel on the panel is charged to a first driving voltage and a touch sensing channel on the panel is charged to a reference voltage, a positive input terminal of the charge amplifier is coupled to the reference voltage through a first switch, the positive input terminal of the charge amplifier is coupled to a first output terminal of the noise cancellation circuit, and a first input terminal of the noise cancellation circuit is coupled to a first pole of the panel;

during the charging period, the positive input end of the output analog buffer of the driving voltage source of the driving channel is coupled to the driving reference voltage through the second switch, and the positive input end of the output analog buffer is coupled to the second output end of the noise elimination circuit;

during the charge transfer period, coupling the touch driving channel to a second driving voltage through a third switch, coupling the touch sensing channel to the negative input terminal of the charge amplifier, and disconnecting the first switch, which couples the positive input terminal of the charge amplifier to the reference voltage, so that the positive input terminal of the charge amplifier is in a floating state, the positive input terminal of the charge amplifier is coupled to the first output terminal of the noise cancellation circuit, and the first input terminal of the noise cancellation circuit is coupled to the first pole of the panel;

during the charge transfer, the second switch, which also couples the positive input terminal of the output analog buffer to the driving reference voltage, is turned off, so that the positive input terminal of the output analog buffer is in a floating state, the positive input terminal of the output analog buffer is coupled to the second output terminal of the noise cancellation circuit, and the second input terminal of the noise cancellation circuit is coupled to the first electrode of the panel;

during the charge transfer, the noise cancellation circuit ac-couples the noise of the first electrode of the panel to the positive input end of the charge amplifier in a floating state after dividing the voltage by the first resistor and the second resistor, so that the voltage of the positive input end of the charge amplifier changes with the noise of the first electrode of the panel, thereby canceling the common mode noise generated by coupling the noise of the first electrode of the panel to the negative input end of the charge amplifier through a parasitic capacitor, and improving the signal-to-noise ratio of capacitive touch sensing;

during the charge transfer period, the noise cancellation circuit ac-couples the noise of the first electrode of the panel to the positive input terminal of the output analog buffer in a floating state after dividing the voltage across the third resistor and the fourth resistor, so that the voltage at the positive input terminal of the output analog buffer changes with the noise of the first electrode of the panel, thereby canceling the common mode noise generated by coupling the noise of the first electrode of the panel to the negative input terminal of the charge amplifier via the parasitic capacitor, and improving the signal-to-noise ratio of capacitive touch sensing, wherein the first driving voltage and the second driving voltage have different potentials.

17. The capacitive touch sensor of claim 16, wherein the first electrode of the panel is a cathode or an anode.

18. The capacitive touch sensor of claim 17, wherein a contact between the first resistor and the second resistor of the noise cancellation circuit is coupled to one end of a plurality of first capacitors and one end of a plurality of second capacitors, the other ends of the plurality of first capacitors are coupled to a plurality of first input terminals, the plurality of first input terminals are coupled to positive input terminals of a plurality of charge amplifiers, and the noise cancellation circuit generates a voltage division by the first resistor and the second resistor and is ac-coupled to the positive input terminals of the plurality of charge amplifiers and the positive input terminal of the output analog buffer in a floating state through the plurality of first capacitors and the second capacitors, respectively, such that voltages of the positive input terminals of the plurality of charge amplifiers and the positive input terminal of the output analog buffer change with the noise of the first electrode of the panel, respectively, and the second driving voltage and the voltages of the positive input terminals of the plurality of charge amplifiers simultaneously cancel the noise.

19. The capacitive touch sensor of claim 17, wherein noise levels of a plurality of voltages at the positive input terminal of the charge amplifier are adjusted by separately adjusting a resistance ratio of the first resistor to the second resistor, and noise levels of the second driving voltage are adjusted by separately adjusting a resistance ratio of the third resistor to the fourth resistor, so as to optimize noise cancellation.