CN117836746A

CN117836746A - Touch signal-to-noise ratio increasing circuit, chip and electronic equipment

Info

Publication number: CN117836746A
Application number: CN202380011950.1A
Authority: CN
Inventors: 谢浩
Original assignee: Shenzhen Goodix Technology Co Ltd
Current assignee: Shenzhen Goodix Technology Co Ltd
Priority date: 2023-11-23
Filing date: 2023-11-23
Publication date: 2024-04-05

Abstract

The embodiment of the application provides a touch signal-to-noise ratio increasing circuit, a chip and electronic equipment, wherein the touch signal-to-noise ratio increasing circuit is characterized in that a first bias resistor and a first-stage operational amplification module are arranged behind an output end of a touch sensor, a first end of the first bias resistor is connected with preset voltage, a second end of the first bias resistor is connected with an output end of the touch sensor, and an in-phase input end of a first-stage operational amplifier is connected. Therefore, the in-phase amplification of the electric signal output by the electric signal receiving module of the touch sensor based on the voltage can be realized, the traditional method for amplifying based on the current is abandoned, the noise gain cannot be increased along with the increase of the load capacitance, the attenuation of the signal output by the touch sensor due to the change of the cathode plate is further reduced, the influence of the increase of the size of the capacitive screen on the SNR signal to noise ratio is reduced, the SNR of the capacitive screen is increased, and the signal precision of the touch sensor of the capacitive screen is improved.

Description

Touch signal-to-noise ratio increasing circuit, chip and electronic equipment

Technical Field

The application relates to the technical field of display screens, in particular to a touch signal-to-noise ratio increasing circuit, a chip and electronic equipment.

Background

The capacitive screen is a screen for further determining a touch position of a user by acquiring an induced current when a human body is touched by means of a touch sensor. With the development of capacitive screen technology, capacitive screens are increasingly being widely used in various display scenes, and the size of the capacitive screens is also increasing.

However, the increase of the size of the capacitive screen can make the size of a Cathode (Cathode) plate arranged in the capacitive screen become larger, and the increase of the size of the capacitive screen can also make the distance between the Cathode plate and the touch sensor become closer and closer, so that the capacitance between the electrode plates becomes larger and larger, and charges are easy to flow away from the Cathode plate more and more. Further, the SNR (Signal Noise Ratio, signal to noise ratio) of the capacitive screen is easy to be lower and lower, and the signal precision of the touch sensor of the capacitive screen is further affected.

In the application, the capacitance between the polar plates is generally called as the load capacitance of the touch sensor, and how to improve the SNR of the capacitive screen under the large-size and large-load capacitance becomes a technical problem to be solved in the field.

Disclosure of Invention

In view of this, the application provides a touch signal-to-noise ratio increasing circuit, a chip and an electronic device, so as to improve the SNR of a capacitive screen under a large-size and large-load capacity.

In a first aspect, the present application provides a touch signal-to-noise ratio increasing circuit, the touch signal-to-noise ratio increasing circuit comprising:

The first offset resistor, the first-stage reverse phase input resistor and the first-stage operational amplification module; the first-stage operational amplification module is an in-phase amplification module;

the first end of the first bias resistor is connected with a preset voltage, the second end of the first bias resistor is connected with the output end of the touch sensor, and the second end of the first bias resistor is connected with the non-inverting input end of the first-stage operational amplifier module;

if the touch signal-to-noise ratio increasing circuit is powered by a single power supply, a first end of the first-stage inverting input resistor is connected with an inverting input end of the first-stage operational amplification module, and a second end of the first-stage inverting input resistor is grounded; or if the touch signal-to-noise ratio increasing circuit is powered by a dual power supply, the first end of the first-stage inverting input resistor is connected with the inverting input end of the first-stage operational amplification module, and the second end of the first-stage inverting input resistor is connected with the preset voltage.

In some possible embodiments, the touch signal-to-noise ratio increasing circuit further includes: a first bias capacitor, wherein:

the first end of the first bias capacitor is connected with the preset voltage, and the second end of the first bias capacitor is connected with the non-inverting input end of the first-stage operational amplification module.

In some possible embodiments, the touch signal-to-noise ratio increasing circuit further includes: a filter, wherein:

the filter is connected with the output end of the first-stage operational amplification module and is used for outputting a target filtering result based on the output result of the first-stage operational amplification module.

In some possible embodiments, the touch signal-to-noise ratio increasing circuit further includes: an analog-to-digital conversion module, wherein:

the analog-to-digital conversion module is connected with the output end of the filter and is used for converting the target filtering result into a target digital signal.

In some possible implementations, the first stage operational amplifier module is a buffer, and the touch signal-to-noise ratio increasing circuit further includes:

the output end of the buffer is connected with the first end of the second-stage non-inverting input resistor, and the second end of the second-stage non-inverting input resistor is connected with the non-inverting input end of the second-stage operational amplification module;

the first end of the second-stage inverting input resistor is connected with the inverting input end of the second-stage operational amplification module, and the second end of the second-stage inverting input resistor is grounded.

the second-stage operational amplifier module, a second-stage non-inverting input resistor and a second-stage inverting input resistor, wherein:

the non-inverting output end of the buffer is connected with the first end of the second-stage non-inverting input resistor, and the second end of the second-stage non-inverting input resistor is connected with the non-inverting input end of the second-stage operational amplification module;

the inverting output end of the buffer is connected with the first end of the second-stage inverting input resistor, and the second end of the second-stage inverting input resistor is connected with the inverting input end of the second-stage operational amplification module.

In some possible implementations, the in-phase amplifying module includes: the in-phase amplifier is connected with the first-stage amplification feedback resistor, the first end of the first-stage amplification feedback resistor is connected with the output end of the in-phase amplifier, and the second end of the first-stage amplification feedback resistor is connected with the inverting input end of the in-phase amplifier.

In some possible embodiments, the touch signal-to-noise ratio increasing circuit further includes:

the second-stage operational amplifier module, a second-stage in-phase input resistor, a second-stage anti-phase input resistor and a filter, wherein:

The first end of the second-stage in-phase input resistor is connected with the output end of the in-phase amplifying module, and the second end of the second-stage in-phase input resistor is connected with the in-phase input end of the second-stage operational amplifying module;

the first end of the second-stage inverting input resistor is connected with the inverting input end of the second-stage operational amplification module, and the second end of the second-stage inverting input resistor is grounded;

and the output end of the second-stage operational amplification module is connected with the filter.

In some possible embodiments, the gain of the in-phase amplification module is less than a preset gain threshold.

In some possible embodiments, the touch signal-to-noise ratio increasing circuit further includes: the second-stage non-inverting input resistor, the second-stage inverting input resistor and the second-stage operational amplification module, wherein:

the in-phase output end of the first-stage operational amplification module is connected with the first end of the second-stage in-phase input resistor, and the second end of the second-stage in-phase input resistor is connected with the in-phase input end of the second-stage operational amplification module;

the inverting output end of the first-stage operational amplification module is connected with the first end of the second-stage inverting input resistor, and the second end of the second-stage inverting input resistor is connected with the inverting input end of the second-stage operational amplification module.

the first control switch, the second control switch, the first differential connecting resistor, the second differential connecting resistor, wherein:

the first end of the first control switch is connected with the second end of the second-stage non-inverting input resistor of the ith path RX channel, the second end of the first control switch is connected with the first end of the first differential connection resistor, and the second end of the first differential connection resistor is connected with the second end of the second-stage inverting input resistor of the (i+1) path RX channel;

the first end of the second control switch is connected with the second end of the second-stage inverting input resistor of the ith path RX channel, the second end of the second control switch is connected with the first end of the second differential connection resistor, and the second end of the second differential connection resistor is connected with the second end of the second-stage non-inverting input resistor of the (i+1) th path RX channel;

the ith path of RX channel and the (i+1) th path of RX channel are two paths adjacent to each other in the multipath Rx channels; the RX channel is a touch signal-to-noise ratio increasing circuit corresponding to the RX electrode.

In some possible implementations, when the first control switch is closed, the in-phase output terminal in the i-th path RX path is adjacent to the opposite-phase output terminal in the i+1-th path RX path by a difference; when the second control switch is closed, the opposite phase output end in the ith path RX channel is adjacent to the in-phase output end in the (i+1) path RX channel for difference, and a target difference result is obtained.

In some possible embodiments, the touch sensor further comprises a reference channel; the reference channel comprises: the first offset resistor, the first-stage reverse phase input resistor and the first-stage operational amplification module; wherein the first-stage operational amplification module is an in-phase amplification module,

the first end of the first bias resistor is connected with a preset voltage, the second end of the first bias resistor is connected with the touch sensor, and the second end of the first bias resistor is connected with the non-inverting input end of the first-stage operational amplifier module;

the first end of the first-stage inverting input resistor is connected with the inverting input end of the first-stage operational amplification module, and the second end of the first-stage inverting input resistor is connected with the preset voltage.

In some possible embodiments, the second stage in-phase input resistor includes: a first second-stage in-phase input resistor, a second-stage in-phase input resistor, the second-stage inverting input resistor comprising: a first second-stage inverting input resistor, a second-stage inverting input resistor, wherein:

a first end of a first second-stage in-phase input resistor in an i-th path RX channel is connected with an in-phase output end of the first-stage operational amplification module, and a second end of the first second-stage in-phase input resistor is connected with a second end of a second-stage in-phase input resistor in the i-th path RX channel and an in-phase input end of the second-stage operational amplification module in the i-th path RX channel;

The first end of the second-stage non-inverting input resistor in the ith path of RX channel is connected with the first end of the second-stage non-inverting input resistor in each path of RX channel and the inverting output end of the reference channel;

a first end of a first second-stage inverting input resistor in the ith path RX channel is connected with an inverting output end of the first-stage operational amplifier module, and a second end of the first second-stage inverting input resistor is connected with a second end of a second-stage inverting input resistor in the ith path RX channel and an inverting input end of a second-stage operational amplifier in the ith path RX channel;

the first end of the second-stage inverting input resistor in the ith path of RX channel is connected with the first end of the second-stage inverting input resistor in each path of RX channel and the in-phase output end in the reference channel;

the in-phase output end of the ith path RX channel is differenced with the anti-phase output end of the reference channel, and the anti-phase output end of the ith path RX channel is differenced with the in-phase output end of the reference channel to obtain a target differential result; the RX channel is a touch signal-to-noise ratio increasing circuit corresponding to the RX electrode, and the reference channel is a touch signal-to-noise ratio increasing circuit corresponding to the reference electrode.

In some possible implementations, the touch signal-to-noise ratio increasing circuit further includes a mean value generating channel;

the mean value generation channel comprises: the device comprises an average value in-phase input resistor, an average value reverse phase input resistor, a second-stage operational amplification module, a filter and a sampling retainer, wherein the average value generation channel is used for collecting the average value of output results of all paths of RX channels.

In some possible embodiments, the second stage in-phase input resistor includes: a first second-stage in-phase input resistor, a second-stage in-phase input resistor, the second-stage inverting input resistor comprising: a first second-stage inverting input resistor and a second-stage inverting input resistor;

the second end of the average value in-phase input resistor is connected with the in-phase input end of the second-stage operational amplification module, the output end of the second-stage operational amplification module is connected with the input end of the filter, and the output end of the filter is connected with the input end of the sampling holder;

each path of RX channel and the mean value generation channel comprises: the first input resistor, the second input resistor, first input capacitor, second input capacitor, wherein:

The first end of a first second-stage in-phase input resistor in an i-th RX channel is connected with the in-phase output end of a first-stage operational amplification module of the i-th channel and the first end of the input first input resistor, and the second end of the first second-stage in-phase input resistor of the i-th RX channel is connected with the second end of a second-stage in-phase input resistor of the i-th RX channel and the in-phase input end of a second-stage operational amplification module of the i-th RX channel;

the first end of the second-stage non-inverting input resistor of the ith path of RX channel is connected with the first end of the second-stage non-inverting input resistor of each path of RX channel and the inverting output end of the second-stage operational amplification module of the average value generation channel;

the first end of the first second-stage inverting input resistor of the ith path RX channel is connected with the inverting output end of the first-stage operational amplification module of the ith path and the first end of the second input resistor; the second end of the first second-stage inverting input resistor of the ith RX channel is connected with the second end of the second-stage inverting input resistor of the ith RX channel and the inverting input end of the second-stage operational amplifier of the ith RX channel;

The first end of the second-stage inverting input resistor of the ith path of RX channel is connected with the first end of the second-stage inverting input resistor of each path of RX channel and the in-phase output end of the second-stage operational amplification module of the average value generation channel;

the second end of the first input resistor is connected with the first end of the mean value in-phase input resistor and the first end of the first input capacitor; the second end of the first input capacitor is grounded;

the second end of the second input resistor is connected with the first end of the mean value inverting input resistor and the first end of the second input capacitor; the second end of the second input capacitor is grounded;

and the in-phase output end of the ith path RX channel is differenced with the opposite-phase output end of the average value generation channel, and the opposite-phase output end of the ith path RX channel is differenced with the in-phase output end of the average value generation channel, so that a target differential result is obtained.

In a second aspect, the present application provides a capacitive screen, where the capacitive screen includes the touch signal-to-noise ratio increasing circuit of any one of the first aspects.

In a third aspect, the present application provides a chip, where the chip includes the touch signal-to-noise ratio increasing circuit of any one of the first aspects.

In a fourth aspect, the present application provides an electronic device, where the electronic device includes the chip in the third aspect.

Compared with the prior art, the beneficial effect that this application embodiment produced lies in:

Drawings

Further details, features and advantages of the present application are disclosed in the following description of exemplary embodiments, with reference to the following drawings, wherein:

FIG. 1 is a schematic diagram of an electrical signal amplifying circuit of a touch sensor commonly used in the prior art;

fig. 2 is a schematic circuit diagram of a touch signal-to-noise ratio increasing circuit according to an embodiment of the present disclosure;

fig. 3 is a schematic circuit diagram of another touch signal-to-noise ratio increasing circuit according to an embodiment of the present disclosure;

fig. 4 is a schematic circuit diagram of another touch signal-to-noise ratio increasing circuit according to an embodiment of the present disclosure;

fig. 5 is a schematic circuit diagram of another touch signal-to-noise ratio increasing circuit according to an embodiment of the present disclosure;

fig. 6 is a schematic circuit diagram of another touch signal-to-noise ratio increasing circuit according to an embodiment of the present disclosure;

fig. 7 is a schematic circuit diagram of another touch signal-to-noise ratio increasing circuit according to an embodiment of the present disclosure;

fig. 8 is a schematic circuit diagram of another touch signal-to-noise ratio increasing circuit according to an embodiment of the present disclosure;

fig. 9 is a schematic circuit diagram of another touch signal-to-noise ratio increasing circuit according to an embodiment of the present disclosure;

Fig. 10 is a schematic circuit diagram of another touch signal-to-noise ratio increasing circuit according to an embodiment of the present disclosure;

fig. 11 is a schematic circuit diagram of another touch signal-to-noise ratio increasing circuit according to an embodiment of the present disclosure;

fig. 12 is a schematic circuit diagram of another touch signal-to-noise ratio increasing circuit according to an embodiment of the present disclosure;

fig. 13 is a schematic diagram showing a technical effect of a measured SNR of a touch signal-to-noise ratio increasing circuit according to an embodiment of the present application.

Detailed Description

Embodiments of the present application will be described in more detail below with reference to the accompanying drawings. While certain embodiments of the present application are shown in the drawings, it is to be understood that the present application may be embodied in various forms and should not be construed as limited to the embodiments set forth herein, but rather are provided to provide a more thorough and complete understanding of the present application. It should be understood that the drawings and examples of the present application are for illustrative purposes only and are not intended to limit the scope of the present application.

The term "including" and variations thereof as used herein are intended to be open-ended, i.e., including, but not limited to. The term "based on" is based at least in part on. The term "one embodiment" means "at least one embodiment"; the term "another embodiment" means "at least one additional embodiment"; the term "some embodiments" means "at least some embodiments. Related definitions of other terms will be given in the description below. It should be noted that the terms "first," "second," and the like herein are merely used for distinguishing between different devices, modules, or units and not for limiting the order or interdependence of the functions performed by such devices, modules, or units.

It should be noted that references to "one" or "a plurality" in this application are intended to be illustrative rather than limiting, and those of ordinary skill in the art will appreciate that "one or more" is intended to be interpreted as "one or more" unless the context clearly indicates otherwise.

In the field of capacitive screens, capacitive screen mutual capacitance detection is to consider a capacitive screen as an induction matrix formed by a plurality of RX electrodes and TX electrodes, and a touch sensor determines a region where finger touch occurs by identifying the RX electrodes and the TX electrodes which specifically generate touch so as to achieve touch identification.

In particular, in capacitive screens, the TX electrodes may be referred to as drive electrodes. The RX electrode may be referred to as an inductive electrode. When the capacitive screen is touched, for example, when a finger touches, the coupling capacitance is changed due to the touch of the finger, and the touch sensor determines a touch area by identifying the changed capacitance value.

Thus, the circuit arranged inside the capacitive screen can be composed of the following partial circuits:

a first part: and acquiring a touch sensor of the touch operation of the user. The touch sensor can be equivalently a circuit combination of the cross-coupled capacitor Cm, the self-capacitance Cr1 between the TX electrode and the cathode plate, the self-capacitance Cr2 between the RX electrode and the cathode plate, and the trace impedance Rr as shown in fig. 1. One end of the touch sensor is connected with the TX electrode, the other end of the touch sensor is connected with the RX electrode, and when the mutual capacitance detection is carried out on the TX electrode and the RX electrode, an excitation signal is input on the TX electrode, and after the combined action of the cross coupling capacitor and the self capacitor in the touch sensor, a response signal is output from the RX electrode end.

A second part: and the amplifying circuit is used for amplifying the response signal output by the touch sensor. The amplifying circuit commonly used in the prior art may be as shown in fig. 1, and the first stage current amplifying module Trans-impedance amplifier (Trans-Impedance Amplifier, TIA) performs current amplification to obtain an amplified response signal.

Third section: and a signal processing circuit for filtering and analog-to-digital converting the amplified response signal to obtain a final target digital signal.

In the second part of the circuit, a transimpedance amplifier commonly used in the prior art acts on the output voltage which varies the input current proportionally, i.e. the transimpedance amplifier is essentially an inverting amplifier. In addition, as described in the background art, when the size of the capacitive screen is gradually increased, the size of the cathode plate is also gradually increased, and the load capacitance of the touch sensor is also gradually increased, which causes the charge signal to flow away from the cathode plate more and more, and further causes the amount of charge entering the transimpedance amplifier to be gradually decreased, so that the output voltage signal amount obtained by the transimpedance amplifier is easily reduced, and further causes the SNR of the capacitive screen circuit to be gradually reduced, and the signal precision of the touch sensor is reduced.

In view of this, the application provides a touch signal to noise ratio increasing circuit, a chip and an electronic device, which are used for increasing the SNR signal to noise ratio of a capacitive screen circuit and improving the accuracy of a touch sensor.

In some embodiments, the touch signal-to-noise ratio increasing circuit provided in the embodiments of the present application may be a composite circuit of the three partial circuits, or may be an amplifying circuit of the second partial circuit, or any combination circuit of the amplifying circuit and circuits of the other two partial circuits.

In some embodiments, the capacitive screen signal-to-noise ratio enhancing circuit provided in the present application may be as shown in fig. 2, and specifically includes the following parts:

the circuit comprises a first bias resistor Rb1, a first-stage reverse-phase input resistor R12 and a first-stage operational amplifier module. Wherein the first-stage operational amplification module is an in-phase amplification module.

Specifically, in some embodiments, the first stage operational amplifier module may include, as shown in fig. 2: the first stage operational amplifier, a first feedback resistor Rf1 and a first feedback capacitor Cf1. The connection relationship between the first feedback resistor Rf1 and the first feedback capacitor Cf1 is shown in fig. 2, and the two are connected in parallel between the inverting input terminal (-) and the non-inverting output terminal (+) of the first stage operational amplifier.

As shown in fig. 2, the connection relationship between the elements of the touch signal-to-noise ratio increasing circuit provided in the embodiment of the present application may be:

the first end of the first bias resistor Rb1 is connected with a preset voltage, the second end of the first bias resistor Rb1 is connected with the output end of the touch sensor, and the second end of the first bias resistor Rb1 is connected with the non-inverting input end (+) of the first-stage operational amplification module;

if the touch signal-to-noise ratio increasing circuit is powered by a single power supply, a first end of the first-stage inverting input resistor R12 is connected with an inverting input end (-) of the first-stage operational amplification module, and a second end of the first-stage inverting input resistor R12 is grounded.

In some embodiments, the touch sensor is equivalent to a capacitor in the mutual capacitance detection process, and the capacitor has the characteristic of only passing an ac signal and not passing a dc signal, so that the dc signal generated in the mutual capacitance detection process cannot enter the amplifying circuit through the touch sensor, and the amplifying circuit needs positive and negative power supplies to supply power. Based on this, in the embodiment of the application, by adding a preset voltage to the touch sensor, the preset voltage is essentially a dc bias power supply, and is used for providing a single power supply for the circuit, and adding a dc bias to the response signal without the dc bias transmitted by the touch sensor, so that the response signal output by the touch sensor can smoothly enter the amplifying circuit for amplification.

As an embodiment, the preset voltage is VCMI (Voltage Control Mode Input, common mode voltage input), which may be 1/2 of the supply voltage of the first stage operational amplifier, preferably the preset voltage VCMI is in the range of 1-2V.

Since the preset voltage is connected to the touch sensor, no impedance exists between the preset voltage VCMI and the first-stage operational amplifier module, at this time, the response signal output by the touch sensor easily flows out from the short circuit of the preset voltage VCMI without entering the first-stage operational amplifier module. Based on this, in the embodiment of the present application, a first bias resistor Rb1 is added between the preset voltage VCMI and the output end of the touch sensor, and the first bias resistor should be a high-impedance resistor, so that the response signal output by the touch sensor cannot flow out from the preset voltage VCMI. As one embodiment, the resistance value of the first bias resistor Rb1 ranges from 2kΩ to 50kΩ, and preferably, the resistance value of the first bias resistor Rb1 is 10kΩ.

Therefore, compared with the scheme that the response signal output by the touch sensor is input into the inverting amplifier to amplify the current in fig. 1, the touch signal-to-noise ratio increasing circuit provided by the embodiment of the invention has the advantages that the response signal output by the touch sensor is input into the non-inverting input end (+) of the first-stage operational amplification module, when the capacitive screen is in single-ended power supply, the direct current bias is increased by means of the preset voltage, under the condition that the load capacitance of the touch sensor is increased, the attenuation of charges caused by the size increase of the cathode plate or the quantity of charges flowing from the cathode plate is reduced, the influence of the size increase of the capacitive screen on the signal-to-noise ratio SNR is reduced, the SNR of the capacitive screen is increased, and the signal precision of the touch sensor of the capacitive screen is improved.

In some embodiments, as shown in fig. 3, the touch signal-to-noise ratio increasing circuit provided in the embodiments of the present application may further include not only the first bias resistor Rb1 but also the first bias capacitor Cb1 between the preset voltage VCMI and the first stage operational amplifier. The first end of the first bias capacitor Cb1 is connected to a preset voltage, and the second end of the first bias capacitor Cb1 is connected to the non-inverting input terminal (+) of the first stage operational amplifier module. Namely, the first bias resistor Rb1 and the first bias capacitor Cb1 are connected in parallel between the output end of the touch sensor and the two ends of the preset voltage output end, and the first bias resistor Rb1 and the first bias capacitor Cb1 are connected in parallel between the non-inverting input end (+) of the first-stage operational amplifier module and the two ends of the preset voltage output end.

Because the capacitive screen detects whether touch control occurs by monitoring the capacitance change between the TX/RX electrodes, the specific coordinate change of the touch control is detected. And because the distance between the touch sensor and the display layer is very close, when the display layer has touch, the display layer is easy to interfere the capacitance change between the TX/RX electrodes, so that the touch sensor detects that errors exist. In the application, the interference generated by the display layer on the capacitance change between the TX/RX electrodes is determined as display interference, and the signal amplitude of the display interference is far beyond the amplitude of the touch signal detected by the touch sensor.

Based on this, in the embodiment of the present application, a first bias capacitor Cb1 is connected in parallel to the first bias resistor Rb1, and a low-pass filter is formed by combining the first bias capacitor Cb1 with the first bias resistor Rb1, so that a display interference signal with high amplitude flows out from the first bias capacitor Cb1 and does not enter the first stage operational amplifier. Therefore, the display interference signal and the common mode interference signal can be effectively reduced and enter the first-stage operational amplification module, and the conversion accuracy of the first-stage operational amplification module is further improved. As an embodiment, the capacitance value of the first bias capacitor Cb1 ranges from 0.5pf to 20pf, and preferably, the capacitance value of the first bias capacitor Cb1 is 10pf.

In some embodiments, if the circuit of the capacitive screen is powered by dual power sources, the touch signal-to-noise ratio increasing circuit provided in the present application is adaptively adjusted based on the dual power source condition, and a specific adjusting circuit structure schematic diagram is shown in fig. 4, in which the second end of the first-stage inverting input resistor R12 is adjusted from original ground to a preset voltage VCMI at the second end of the first-stage inverting input resistor R12, and the other circuits are not adjusted.

In the embodiment of the application, under the condition that the capacitive screen supplies power to the dual power sources, one power source is connected to the preset voltage VCMI through the first bias resistor Rb1, and the other power source is connected to the preset voltage VCMI through the first-stage inverting input resistor R12. Therefore, the touch signal to noise ratio increasing circuit provided by the application is not only suitable for a capacitive screen powered by a single power supply, but also suitable for a capacitive screen powered by double power supplies.

In some embodiments, the power supply of the capacitive screen is divided into two types: the voltage range of the analog power supply is as follows: 2.6V-3.6V, the voltage range of the digital power supply is as follows: the specific power supply of 1.8V-3.3V depends on the main board of the capacitive screen. If the analog power supply or the digital power supply is used for supplying power in a mode of selecting one of the analog power supply and the digital power supply to supply power for the single power supply, the analog power supply and the digital power supply are used for supplying power for the double power supplies.

In some embodiments, as shown in fig. 5, the touch signal-to-noise ratio increasing circuit provided in the present application may further include: a filter. The filter is connected with the output end of the first-stage operational amplification module and is used for outputting a target filtering result based on the output result of the first-stage operational amplification module.

The internal circuit structure of the filter in fig. 5 and the connection relationship between the internal elements can be referred to as a circuit configuration diagram shown in fig. 6. Specifically, the filter internal components include: the filter amplifier comprises a filter amplifier, a first filter input resistor, a second filter input resistor, a filter input capacitor, a filter feedback resistor and a filter feedback capacitor. Wherein, the connection relation between each component is:

The first end of the filter input capacitor is connected with the first end of the first filter input resistor and the inverted output end (-) of the first-stage operational amplification module, and the second end of the filter input capacitor is connected with the first end of the second filter input resistor and the in-phase output end (+) of the first-stage operational amplification module.

The second end of the first filter input resistor is connected with the non-inverting input terminal (+) of the filter amplifier. The second terminal of the second filter input resistor is connected to the inverting input (-) of the filter amplifier.

One end of a filter feedback resistor is connected with the first end of the first filter input resistor, the other end of the filter feedback resistor is connected with the first filter output end (-) of the filter amplifier, one end of a filter feedback capacitor is connected with the second end of the first filter input resistor, and the other end of the filter feedback capacitor is connected with the first filter output end (-) of the filter amplifier; one end of the other filtering feedback resistor is connected with the first end of the second filtering input resistor, the other end of the other filtering feedback resistor is connected with the second filtering output end (+) of the filtering amplifier, one end of the one filtering feedback capacitor is connected with the second end of the second filtering input resistor, the other end of the one filtering feedback capacitor is connected with the second filtering output end (+) of the filtering amplifier, and the specific electric signal conversion process can be described with reference to the working principle of other filters.

In some embodiments, the touch signal to noise ratio increasing circuit may further include an analog to digital conversion ADC module based on the presence of the filter. The analog-to-digital conversion ADC module is connected with the output end of the filter and is used for converting the target filtering result into a target digital signal.

In this application, the first-stage operational amplification module in the touch signal-to-noise ratio increasing circuit provided in the embodiment of the present application is essentially an in-phase amplification module, that is, a voltage amplification circuit that increases input impedance through negative feedback, and the type of the voltage amplification circuit may be a buffer with an in-phase amplification function or an in-phase amplifier with an in-phase amplification function. The in-phase amplifier can be a common single-power in-phase amplifier, a dual-power in-phase amplifier, a fixed-gain in-phase amplifier, or a gain-adjustable PGA (Programmable Gain Amplifier, programmable gain in-phase amplifier).

In some embodiments, when the first stage operational amplifier module is a buffer with an in-phase amplifying function, and the buffer outputs a single-ended signal, the circuit structure of the touch signal-to-noise ratio increasing circuit provided in the embodiments of the present application may be as shown in fig. 7, and further includes:

The second-stage operational amplifier module, a second-stage non-inverting input resistor R21 and a second-stage inverting input resistor R22. The connection relationship between the circuit elements is as shown in fig. 7:

the output end of the buffer is connected with the first end of a first second-stage non-inverting input resistor R21, and the second end of the first second-stage non-inverting input resistor R21 is connected with the non-inverting input end (+) of the second-stage operational amplification module;

the first end of the first second-stage inverting input resistor R22 is connected with the inverting input end (-) of the second-stage operational amplification module, and the second end of the first second-stage inverting input resistor R22 is grounded.

In some embodiments, the first-stage operational amplification module is a buffer with an in-phase amplification function, and the buffer outputs a fully differential signal, and a circuit structure of the touch signal-to-noise ratio increasing circuit provided in the embodiments of the present application may be shown in fig. 8, and further includes:

the second-stage operational amplifier module, the first second-stage non-inverting input resistor R21 and the first second-stage inverting input resistor R22. The connection relationship between the circuit elements is as shown in fig. 8:

the non-inverting output end of the buffer is connected with the first end of a first second-stage non-inverting input resistor R21, and the second end of the first second-stage non-inverting input resistor R21 is connected with the non-inverting input end (+) of the second-stage operational amplification module;

The inverting output end of the buffer is connected with the first end of the first second-stage inverting input resistor R22, and the second end of the first second-stage inverting input resistor R22 is connected with the inverting input end (-) of the second-stage operational amplifier module.

The second-stage operational amplifier module in fig. 7 and 8 is shown as a diagram, and is composed of a second-stage operational amplifier, two groups of second feedback resistors Rf2 and a second feedback capacitor Cf2, wherein the connection relationship between the internal elements of the second-stage operational amplifier module is as follows:

one group of second feedback resistors Rf2 and second feedback capacitors Cf2 are connected in parallel between the inverting input terminal (-) and the non-inverting output terminal (+) of the second-stage operational amplifier, and the other group of second feedback resistors Rf2 and second feedback capacitors Cf2 are connected in parallel between the non-inverting input terminal (+) and the non-inverting output terminal (-) of the second-stage operational amplifier. The values of the two groups of second feedback resistors Rf2 and the second feedback capacitor Cf2 may be the same or different, and specifically, the values may be flexibly adjusted according to actual requirements, which is not strictly limited in the application.

Since the gain of the buffer may be fixed, there are cases where the amplification gain of the buffer is insufficient to amplify the response signal output by the touch sensor to meet the input voltage requirement of the filter. According to the embodiment of the application, the second-stage operational amplification module is connected to the output end of the buffer, and the second-stage operational amplification module is used for carrying out secondary amplification on the amplified response signal after the response signal is amplified by the first-stage operational amplification module, so that the response signal output by the touch sensor can be amplified to meet the requirement of the input voltage of the filter.

In some embodiments, the touch signal-to-noise ratio increasing circuit provided in the embodiments of the present application may also be as shown in fig. 9, where the first operational amplifying module (a part of circuits in a left dashed box in the figure) is formed by combining a simple in-phase amplifier AMP and a first feedback resistor Rf 1. As shown in fig. 9, the touch signal-to-noise ratio increasing circuit provided in the embodiment of the present application may further include:

the second-stage operational amplifier module, the first second-stage non-inverting input resistor R21 and the first second-stage inverting input resistor R22, wherein the connection relationship between the elements can be as shown in fig. 9:

a first terminal of the first feedback resistor Rf1 is connected to the output terminal of the in-phase amplifier AMP, and a second terminal of the first feedback resistor Rf1 is connected to the inverting input terminal (-) of the in-phase amplifier AMP.

The first end of the first second-stage in-phase input resistor R21 is connected with the output end of the in-phase amplifier AMP, and the second end of the first second-stage in-phase input resistor R21 is connected with the in-phase input end (+) of the second-stage operational amplifier module.

The output end of the second-stage operational amplification module is connected with the filter.

In some embodiments, when the gain of the buffer or the gain of the in-phase amplifier AMP is sufficient to amplify the response signal output by the touch sensor to the input voltage requirement of the filter, the second-stage operational amplification module and the corresponding second-stage in-phase input resistor and second-stage opposite-phase input resistor may be omitted, the first-stage operational amplification module is directly connected with the filter, and the amplified response signal is directly input into the filter for filtering processing, so as to obtain the target filtered signal.

If the gain of the buffer or the gain of the in-phase amplifier AMP is smaller than a preset gain threshold value, a second-stage operational amplification module is additionally arranged between the first-stage operational amplification module and the filter, the second-stage operational amplification module carries out secondary amplification on the amplified response signal, and then the signal after secondary amplification is input into the filter for filtering processing, so that a target filtering signal is obtained.

In some embodiments, the second-stage operational amplification module may be a programmable gain amplifier, and the amplification gain of the second-stage operational amplification module may be adjusted by software, so as to achieve that the amplification gain of the amplifying circuit obtained by combining the first-stage operational amplification module and the second-stage operational amplification module meets the requirement.

Because the mutual capacitance detection of the capacitive screen is realized by taking the capacitive screen as an induction matrix formed by a plurality of RX electrodes and TX electrodes, the touch sensor determines the specific touch coordinates of a touch point triggered by a user based on the difference of response signals output by the TX electrodes and the RX electrodes under the action of excitation signals. Based on this, in order to improve the SNR of the whole capacitive screen, the touch signal-to-noise ratio increasing circuit provided in the embodiments of the present application may be connected to each RX electrode. As another implementation manner, the touch signal-to-noise ratio increasing circuit provided in the embodiment of the application may be optionally connected to a part of the RX electrodes, and the specific access number may be flexibly selected based on actual operation.

The touch signal-to-noise ratio amplifying circuit can increase the signal-to-noise ratio of touch detection so as to improve the sensitivity of the touch detection. Based on this, in some embodiments, the signal-to-noise ratio increasing circuits of each way are of the same type. The RX channels can flexibly select different signal-to-noise ratio increasing circuits based on the difference of each output signal.

When the capacitive screen is in touch, the coupling capacitance between the TX electrode and the RX electrode can change, and the specific touch position is determined by determining the change of the coupling capacitance in the touch detection process of the capacitive screen. In the method, the reference capacitance is set as a comparison standard, the difference condition between the coupling capacitance and the reference capacitance is determined, whether the coupling capacitance changes or not is determined, and the size of the change is determined. The method for carrying out capacitive screen touch detection based on the difference condition between the coupling capacitance and the reference capacitance is a differential detection method.

The touch signal-to-noise ratio increasing circuit provided by the application can specifically comprise preset voltage VCMI, a first bias resistor Rb1, a first-stage operational amplification module, a first second-stage in-phase input resistor R21, a first second-stage opposite-phase input resistor R22, a second-stage operational amplification module, a filter and a sampling holder as shown in fig. 10-12 under the application scene of the differential detection method, namely the scene that the touch sensor is used for differential detection.

In the connection relationship between each element of the touch signal-to-noise ratio increasing circuit corresponding to each RX electrode, the connection relationship between the preset voltage VCMI, the first bias resistor Rb1 and the cross-coupling capacitor Cm is the same as the connection relationship between the preset voltage VCMI, the first bias resistor Rb1 and the touch sensor, where the cross-coupling capacitor Cm is a coupling capacitor formed between each RX electrode and each TX electrode.

The first-stage operational amplifier module may be a first-stage operational amplifier module shown in any one of fig. 2 to 9, wherein the first-stage operational amplifier module circuit shown in the left dashed-line box in fig. 10 to 12 is an in-phase amplifier module formed by combining the first-stage operational amplifier AMP with the first feedback resistor Rf1 and the first feedback capacitor Cf1, and the first feedback resistor Rf1 and the first feedback capacitor Cf1 are connected in parallel to the negative feedback circuit of the first-stage operational amplifier, taking the first-stage operational amplifier module in fig. 2 as an example.

The connection relationship between the elements in the touch signal-to-noise ratio increasing circuit may be as shown in fig. 10 to 12:

the in-phase output end of the first-stage operational amplification module is connected with the first end of a first second-stage in-phase input resistor R21, and the second end of the first second-stage in-phase input resistor R21 is connected with the in-phase input end (+) of the second-stage operational amplification module.

The inverting output end of the first-stage operational amplifier module is connected with the first end of the first second-stage inverting input resistor R22, and the second end of the first second-stage inverting input resistor R22 is connected with the inverting input end (-) of the second-stage operational amplifier module.

The inverting output end (-) of the second-stage operational amplification module is connected with the non-inverting input end (+) of the filter, the non-inverting output end (+) of the second-stage operational amplification module is connected with the inverting input end (-) of the filter, the first filtering output end (-) of the filter is connected with the first input end (Vin 1) of the sampling holder, and the second filtering output end (+) of the filter is connected with the second input end (Vin 2) of the sampling holder.

The first sampling output end of the sampling holder in the touch signal-to-noise ratio increasing circuit corresponding to each path of RX electrode is connected with the non-inverting input end (+) of the analog-to-digital conversion buffer, and the second sampling output end of the sampling holder in the touch signal-to-noise ratio increasing circuit corresponding to each path of RX electrode is connected with the inverting input end (-) of the analog-to-digital conversion buffer.

As shown in fig. 10 to 12, the sample holder includes a sample holding capacitor C1, a sample holding capacitor C2, and switches S1 to S4. The first end of the switch S1 is connected with the first filtering output end of the filter, the second end of the switch S1 is connected with the first end of the sample-hold capacitor C1 and the first end of the switch S3, the second end of the sample-hold capacitor C1 is grounded, and the second end of the switch S3 is connected with the second ends of the switches S3 of the sample holders of other paths RX channels and the non-inverting input end (+) of the analog-to-digital conversion buffer.

The first end of the switch S2 is connected with the second filtering output end of the filter, the second end of the switch S2 is connected with the first end of the sample-hold capacitor C2 and the first end of the switch S4, the second end of the sample-hold capacitor C2 is grounded, and the second end of the switch S4 is connected with the second ends of the switches S4 of the sample holders of other paths RX channels and the inverting input end (-) of the analog-to-digital conversion buffer.

The switches S1 to S4 are controlled to be closed or opened based on the high and low levels of the sampling clock, and specifically, as an embodiment, the switches are closed when the sampling clock is high and opened when the sampling clock is low. The specific control mode can be flexibly set according to actual requirements, and the application is not strictly limited.

When the switch S1 and the switch S3 are closed, the in-phase output signal output by the filter enters the sampling holder to be sampled, when the switch S1 and the switch S3 are opened, the sampling holder keeps outputting the in-phase output signal, and similarly, when the switch S2 and the switch S4 are closed, the anti-phase output signal output by the filter enters the sampling holder to be sampled, and when the switch S2 and the switch S4 are opened, the sampling holder keeps outputting the anti-phase output signal. The principles of signal holding and signal output of the sample holder may refer to the technical documents of the relevant sample holders, and will not be described herein.

In this application, the naming of the in-phase output end and the opposite-phase output end of each element may be replaced by other naming forms, but it is required to ensure that the signal polarity of the signal output from the touch signal-to-noise ratio increasing circuit corresponding to each RX electrode to the in-phase input end (+) of the analog-to-digital conversion buffer remains consistent, and ensure that the signal polarity of the signal output from each RX channel to the opposite-phase input end (-) of the analog-to-digital conversion buffer remains consistent.

The inverting output terminal (-) of the analog-to-digital buffer is connected with the first input terminal (Vin 1) of the analog-to-digital conversion module ADC, and the non-inverting output terminal (+) of the analog-to-digital buffer is connected with the second input terminal (Vin 2) of the analog-to-digital conversion module ADC. The analog-to-digital buffer is essentially an in-phase amplifying follower and is used for indirectly providing a transient current for the analog-to-digital conversion module ADC, so that the ADC is prevented from acquiring the current from the sample holder, and inaccurate analog-to-digital conversion results are further caused.

In this embodiment of the present application, the second-stage operational amplifier module may also be a PGA amplifier, and the PGA amplifier is used when the gain of the first-stage operational amplifier module is smaller than a preset gain threshold. The PGA amplifier may not be used when the gain of the first stage op amp module meets a preset gain threshold condition. The preset gain threshold condition may be that the voltage amplitude of the amplified output signal of the first-stage operational amplification module meets the filter input voltage amplitude of the filter, the specific threshold may be set according to actual experience, or may be set according to experimental test results, and the application is not strictly limited.

Since the types of differential detection are classified into various types, such as adjacent differential detection, reference channel subtraction differential detection, average subtraction differential detection, and the like. The adjacent differential detection is to determine the touch area through the variation difference between the coupling capacitances of adjacent RX electrodes. Based on this, for the situation of adjacent differential detection, the touch signal-to-noise ratio increasing circuit corresponding to each RX electrode includes a preset voltage VCMI, a first bias resistor Rb1, a first-stage inverting input resistor R12, a first-stage operational amplification module, a second-stage normal-phase input resistor R21, a first-stage second-stage inverting input resistor R22, a second-stage operational amplification module, a filter, a sample holder, and an analog-to-digital conversion buffer and an analog-to-digital conversion module ADC shared in the touch signal-to-noise ratio increasing circuit corresponding to each RX electrode, where the touch signal-to-noise ratio increasing circuit under adjacent differential detection provided in the present application may be as shown in fig. 10, and the touch signal-to-noise ratio increasing circuit provided in the embodiment of the present application further includes:

The first control switch K1, the second control switch K2, the first differential connection resistor R1 and the second differential connection resistor R2.

For convenience of description, the touch signal-to-noise ratio increasing circuit corresponding to the RX electrode is hereinafter referred to as an "RX channel".

The connection relationship between the elements of adjacent RX channels is shown in fig. 10:

the first end of the first control switch K1 is connected with the second end of the first second-stage non-inverting input resistor R21 of the ith path RX channel, the second end of the first control switch K1 is connected with the first end of the first differential connecting resistor R1, and the second end of the first differential connecting resistor R1 is connected with the second end of the first second-stage inverting input resistor R22 of the (i+1) path RX channel;

the first end of the second control switch K2 is connected with the second end of the first second-stage inverting input resistor R22 of the ith path RX channel, the second end of the second control switch K2 is connected with the first end of the second differential connecting resistor R2, and the second end of the second differential connecting resistor R2 is connected with the second end of the first second-stage non-inverting input resistor R21 of the (i+1) path RX channel;

the principle of differential detection is to detect whether the coupling capacitance Cm of the RX channel is changed compared with the reference channel, and if so, the capacitive screen is indicated to be touched. That is, if the capacitive screen is not touched, the difference value between the coupling capacitances Cm between the adjacent channels should be kept stable, and if the difference value between the coupling capacitances Cm between the adjacent channels changes, it indicates that there is a touch between the adjacent RX electrodes.

Based on this, in the embodiment of the present application, when the first control switch K1 is closed, the in-phase output result of the first stage operational amplification module of the i-th path RX path is input to the inverting input end of the second stage operational amplification module of the i+1th path RX path, and since there is a phase opposite between the in-phase output result of the i-th path RX path and the phase of the inverting output result of the i+1th path RX path, the two processes an addition operation, which is equivalent to the difference between the two, and a difference result is obtained, that is, if there is a difference between adjacent RX paths, if there is a difference, it is indicated that a touch is generated in one of the RX electrodes, and it can be further determined which path in the adjacent paths is specifically touched based on the result obtained by the difference.

Similarly, when the second control switch K2 is closed, the inverted output result of the first-stage operational amplification module of the ith RX channel is adjacent to the in-phase output result of the first-stage operational amplification module of the (i+1) th RX channel, and further, based on the result obtained by the difference, it is further determined which channel in the adjacent RX electrodes is touched.

In one embodiment, the first control switch K1 and the second control switch K2 may be clocked to be closed simultaneously based on the control signal, which may help to determine the difference in coupling capacitance between adjacent RX electrodes simultaneously, and further determine which RX electrode is touched more precisely.

And each path of RX channel enters a second-stage operational amplification module PGA after adjacent difference making results of other adjacent channels, the second-stage operational amplification module carries out secondary amplification on the adjacent difference making results, then enters an analog-to-digital conversion module ADC through a sampling holder and an analog-to-digital conversion buffer to output a digital signal matrix of the difference making results after adjacent difference making of each path of RX channel, and the position coordinates corresponding to the touch can be determined according to the values of each element in the digital signal matrix.

By selecting the embodiment of the application, the adjacent differential detection of multiple channels can be realized, and particularly, when the adjacent differential detection is carried out, the result of the adjacent differential detection can be obtained by subtracting the conversion results of the adjacent channels. And, because switch K1 and switch K2 are closed simultaneously the back, two signal lines have formed the difference signal line, when there is the display interference noise, display interference noise can couple to these two difference signal lines simultaneously, when doing adjacent difference between adjacent RX passageway, this display interference noise is common mode noise, will be offset completely, and then reduced the interference of display interference to the differential result of target, further improved the output result precision of touch-control signal to noise ratio increase circuit.

In this embodiment, when the first control switch K1 and the second control switch K2 between the RX channels are both turned off, the capacitive screen touch detection used between the RX channels is single-channel touch detection, instead of differential detection. By adopting the embodiment of the application, the flexible selection of the touch detection mode can be realized by controlling whether the first control switch K1 and the second control switch K2 between the paths of RX channels are simultaneously closed.

Based on the adjacent channel differential detection principle, the output result of each channel needs to be calculated continuously, and the calculation amount needed to be executed is large, so that the algorithm processing is complicated. To save the complexity of the algorithm processing, in some embodiments, the algorithm processing complexity is reduced by subtracting the reference channel differential detection circuitry. Wherein, as shown in fig. 11, the reference channel includes: the first bias resistor Rb1, the first-stage reverse phase input resistor R12 and the first-stage operational amplifier module; wherein the first-stage operational amplification module is an in-phase amplification module,

the first end of the first bias resistor Rb1 is connected with a preset voltage VCMI, the second end of the first bias resistor Rb1 is connected with the touch sensor, and the second end of the first bias resistor Rb1 is connected with the non-inverting input end (+) of the first-stage operational amplification module;

The first end of the first-stage inverting input resistor R12 is connected with the inverting input end (-) of the first-stage operational amplifier module, and the second end of the first-stage inverting input resistor R12 is connected with the preset voltage VCMI.

On this basis, as an implementation manner, the touch signal-to-noise ratio increasing circuit for the case of differential detection of the reference channel subtraction in the embodiment of the present application may be as shown in fig. 11:

except for a preset voltage, a first bias resistor Rb1, a first-stage operation module, a filter, a sampling holder and a second-stage operation amplification module which are possibly included in each path of RX channel, the second-stage in-phase input resistor in the touch signal-to-noise ratio increasing circuit corresponding to each RX electrode for subtracting the differential detection of the reference channel comprises two second-stage in-phase input resistors (R21 and R23) and two second-stage anti-phase input resistors (R22 and R24).

The first-stage operational amplifier module is an in-phase amplifying module formed by combining a first-stage operational amplifier, a first feedback resistor Rf1 and a first feedback capacitor Cf1 as shown in a dashed line box in fig. 11, and similarly, the first feedback resistor Rf1 and the first feedback capacitor Cf1 are connected in parallel to a negative feedback circuit of the first-stage operational amplifier.

The second-stage operational amplification module is also selected according to the gain of the first-stage operational amplification module, and the second-stage in-phase input resistor and the second-stage anti-phase input resistor are directly connected with the filter under the condition that the second-stage operational amplification module is not needed.

As a connection mode, the connection relation of each element in the capacitive screen signal-to-noise ratio circuit under the condition of subtracting reference channel differential detection is shown in fig. 11:

the first end of a first second-stage non-inverting input resistor R21 in the ith path RX channel is connected with the non-inverting output end of the first-stage operational amplification module, and the second end of the first second-stage non-inverting input resistor R21 is connected with the second end of a second-stage non-inverting input resistor R23 of the ith path RX channel and the non-inverting input end (+) of the second-stage operational amplification module of the ith path.

The first end of the second-stage non-inverting input resistor R23 of the ith path RX channel is connected with the first ends of the second-stage non-inverting input resistors R23 of other paths RX channels, and the first ends of the second-stage non-inverting input resistors R23 of the other paths RX channels are connected with the inverting output ends of the reference channels.

The first end of the first second-stage inverting input resistor R22 of the ith path RX channel is connected with the inverting output end of the first-stage operational amplifier module, and the second end of the first second-stage inverting input resistor R22 is connected with the second end of the second-stage inverting input resistor R24 of the ith path RX channel and the inverting input end (-) of the second-stage operational amplifier of the ith path.

The first end of the second-stage inverting input resistor R24 of the ith path RX channel is connected with the first end of the second-stage inverting input resistor R24 of each path RX channel and the in-phase output end of the reference channel.

The in-phase output end of the ith RX channel is differenced with the opposite-phase output end of the reference channel, and the opposite-phase output end of the ith RX channel is differenced with the in-phase output end of the reference channel, so that a target differential result is obtained.

Specifically, the reference channel is a touch signal-to-noise ratio increasing circuit corresponding to the reference electrode, wherein the reference electrode may be an Rx electrode, and the Rx electrode may be a target channel selected from Rx0 to RXn, or may be an external electrode, for example, a circle of preset test points around the capacitive screen, or may be a cathode plate.

If the adjacent differential detection is based on the difference value between the coupling capacitances of the adjacent channels, the subtracting fixed channel or the subtracting reference channel differential detection is based on detecting the difference value between the coupling capacitances of the RX channels and the coupling capacitance of the fixed channel, and determining whether the RX channels have touches. Based on this, in the embodiment of the application, each path of RX channel makes a difference between the in-phase output result of the first stage operational amplification module and the in-phase output result of the reference channel, can determine whether the coupling capacitance of each path of RX channel changes compared with the coupling capacitance of the reference channel, and then outputs the difference result of each path of RX channel through the second stage operational amplification module, the filter, the sample holder, the analog conversion buffer and the analog-to-digital conversion module, and based on each element value in the digital signal matrix, can determine the area where touch occurs.

In the embodiment of the application, adjacent channels are not subtracted from each other, but reference channels RXm are introduced, the signals of all channels are subtracted from each other by the signals of all channels to obtain the output result of each channel, namely, the effect of differential detection is realized by RX0-RXm and RX1-RXm, so that each channel can obtain the result of the channel by subtracting the reference channels, the operation process is simpler, and the realization difficulty is lower.

In some embodiments, the detection of whether a touch has occurred on each RX channel of the capacitive screen may be performed by means of subtractive differential detection. Specifically, as an implementation manner, the touch signal to noise ratio increasing circuit under the reduced average differential detection provided in the embodiment of the present application may be as shown in fig. 12, and further include a path of average value generating channel on the basis of each path of RX channel, where the average value generating channel includes: the average value generation channel is used for collecting output results of all paths of RX channels and calculating to obtain an average value of the output results.

For each path of RX channel, the second-stage non-inverting input resistor also includes a first second-stage non-inverting input resistor R21 and a second-stage non-inverting input resistor R23, and the second-stage inverting input resistor also includes a first second-stage inverting input resistor R22 and a second-stage inverting input resistor R24.

As shown in fig. 12, the method includes: a first input resistor RA1, a second input resistor RA2, a first input capacitor CA1, and a second input capacitor CA2.

As shown in fig. 12, the connection relationship between each element in the touch signal-to-noise ratio increasing circuit under the reduced-average differential detection is as follows:

the second end of the mean value in-phase input resistor RS1 is connected with the in-phase input end (+) of the second-stage operational amplification module, the second end of the mean value in-phase input resistor RS2 is connected with the in-phase input end (-) of the second-stage operational amplification module, the output end of the second-stage operational amplification module is connected with the input end of the filter, and the output end of the filter is connected with the input end of the sampling holder.

The first end of a first second-stage in-phase input resistor R21 in the ith RX channel is connected with the in-phase output end of the first-stage operational amplification module in the ith channel and the first end of the input first input resistor RA1, and the second end of the first second-stage in-phase input resistor R21 in the ith RX channel is connected with the second end of a second-stage in-phase input resistor R23 in the ith RX channel and the in-phase input end (+) of the second-stage operational amplification module in the ith RX channel.

The first end of the second-stage non-inverting input resistor R23 of the ith path RX channel is connected with the first end of the second-stage non-inverting input resistor R23 of each path RX channel and the inverting output end (-) of the second-stage operational amplifier module of the average value generation channel.

The first end of the first second-stage inverting input resistor R22 of the ith path RX channel is connected with the inverting output end of the first-stage operational amplifier module of the ith path and the first end of the second input resistor RA 2; the second end of the first second-stage inverting input resistor R22 of the ith RX channel is connected with the second end of the second-stage inverting input resistor R24 of the ith RX channel and the inverting input end (-) of the second-stage operational amplifier of the ith RX channel.

The first end of the second-stage inverting input resistor R24 of the ith path RX channel is connected with the first end of the second-stage inverting input resistor R24 of each path RX channel and the non-inverting output end (+) of the second-stage operational amplifier module of the average value generation channel.

The second end of the first input resistor RA1 is connected with the first end of the mean value in-phase input resistor RS1 and the first end of the first input capacitor CA 1; the second terminal of the first input capacitor CA1 is grounded.

The second end of the second input resistor RA2 is connected with the first end of the mean value inverting input resistor RS2 and the first end of the second input capacitor CA 2; the second terminal of the second input capacitor CA2 is grounded.

The in-phase output end of the ith RX channel is differed from the opposite-phase output end of the average value generation channel, and the opposite-phase output end of the ith RX channel is differed from the in-phase output end of the average value generation channel, so that a target differential result is obtained.

The average value generation channel is equivalent to an addition circuit, the output values of all channels are accumulated, and then the gain is set by means of the input resistor RA to achieve the effect of dividing the channel number, so that an output average value is obtained. The first input capacitor CA1 and the second input capacitor CA2 added in the average value generating channel circuit are used for filtering high-frequency interference signals existing in the average value signals.

Similar to the differential detection of the adjacent differential detection and the reference channel differential detection, in the embodiment of the application, after the in-phase output end and the opposite-phase output of each channel RX channel are input to the second-stage operational amplification module of the average value generation channel, average value calculation is performed, and the in-phase output result average value and the opposite-phase output result average value of each RX channel are output. And then, the average value of the in-phase output result and the average value of the reverse-phase output result are subjected to difference with the in-phase output result and the reverse-phase output result of each path of RX channel. Specifically, the in-phase output result of each path of RX channel is differenced with the average value of the in-phase output result of the average value generation channel, the difference between the coupling capacitance of each path of RX channel and the average value of the coupling capacitance change of each path of RX channel is obtained, and the specific path of RX channel is determined.

According to the embodiment of the application, the average value generation channel is used for collecting the output results of all the RX channels and obtaining the average value, and then when the average value is output, the output result of each channel of RX channel is subtracted from the average value, so that differential reduction is not needed, and the problem of noise accumulation caused by white noise introduced in the differential reduction process can be effectively reduced.

Compared with the touch signal-to-noise ratio increasing circuit of adjacent differential detection, the touch signal-to-noise ratio increasing circuit of the average value reduction channel differential detection is realized in circuit engineering, the module wire-outgoing mode is similar to that of single-ended signals, wires on a circuit board do not need to be arranged strictly according to a fixed wire sequence, and design cost and processing cost are saved.

In a second aspect, the present application further proposes a capacitive screen, where the capacitive screen includes the touch signal-to-noise ratio increasing circuit described above.

In a third aspect, the present application further proposes a Chip, which includes the above-mentioned touch signal-to-noise ratio increasing circuit, and the Chip (Integrated Circuit, IC) is also referred to as a Chip, and the Chip may be, but is not limited to, a SOC (System on Chip) Chip, a SIP (System in package) Chip. The chip can effectively solve the problem that the signal to noise ratio is reduced due to the fact that the size of the capacitive screen is gradually increased through the touch signal to noise ratio increasing circuit arranged inside the chip.

Specifically, the touch signal-to-noise ratio increasing circuit is connected with each RX channel of the capacitive screen through each pin of the chip, and for the case that RX is single-ended output, the touch signal-to-noise ratio increasing circuits after each RX channel can be the same or different. For the case where RX is a differential output, flexible selection may be made based on three embodiments of differential detection, which is not strictly limited in this application.

The voltage-amplified touch signal-to-noise ratio increasing circuit with high impedance input belongs to a novel scheme, and the obtained actual measurement SNR is superior to that of the original current amplification scheme, as can be seen from the actual measurement SNR curve result shown in fig. 13, when the size of the capacitive screen is increased. Specifically, the following formula can clearly show that the signal to noise ratio of the capacitive screen provided by the application is superior to that of the traditional scheme:

with reference to the circuit diagram shown in fig. 1, it can be deduced through circuit theory that the signal gain of the original scheme satisfies the following formula 1):

Signal Gain≈sC _M R _f formula 1

Where s is a signal, C in the formula _M R is the capacitance of the input capacitor _f Is the resistance of the feedback resistor.

The noise gain of the original scheme satisfies the following equation 2):

Noise Gain≈1+sC _r R _f Formula 2

Wherein C in the formula _r R is the capacitance of the input capacitor _f Is the resistance of the feedback resistor.

According to the formulas 1) and 2), it can be seen that the noise gain and the signal gain have positive correlation with the resistance value of the feedback resistor and the capacitance value of the input capacitor, and the larger the capacitance value change of the input capacitor is, the larger the noise gain is, and the lower the signal to noise ratio is.

According to the touch signal-to-noise ratio increasing circuit shown in fig. 2 provided by the present application, the signal gain of the new scheme can be calculated according to the circuit theory to satisfy the following formula 3):

Signal Gain≈(1+R _f /RG1)(s C _M R _b /1+s C _r R _b ) Formula 3

Wherein s is a signal, C _M R is the capacitance of the input capacitor _f R is the resistance of the feedback resistor _b The resistance of the first bias resistor RG1 is the resistance of the first ground resistor.

The noise gain of the new scheme satisfies the following equation 4):

Noise Gain≈1+R _f RG 1. Eq. Formula 4)

According to the formula 3) and the formula 4), the noise gain of the new scheme is irrelevant to the input capacitance, so that the change of the input capacitance does not affect the noise gain, and noise is not introduced, thereby reducing noise interference. And secondly, the noise gain is only in positive correlation with the ratio between the resistance value of the feedback resistor and the resistance value of the grounding resistor, and the noise gain can be controlled by selecting the grounding resistor and the feedback resistor with proper magnitudes.

According to the embodiment of the application, the signal-to-noise ratio increasing circuit arranged in the capacitive screen can be flexibly selected according to actual needs, so that display interference and common mode interference are reduced, and the signal response effect and the display effect of the capacitive screen are improved.

In a fourth aspect, the present application further proposes an electronic device including a touch signal-to-noise ratio increasing circuit. Specifically, the electronic device includes a device main body and a chip as described above disposed in a device theme. The electronic device may be, but is not limited to, any electronic device including a display screen, such as a smart television, a display, a cell phone, a smart tablet, and the like. According to the electronic equipment, the problem that the signal to noise ratio is reduced due to the fact that the size of the capacitive screen is gradually increased can be effectively solved through the touch signal to noise ratio increasing circuit arranged inside the electronic equipment.

The foregoing description is not intended to limit the preferred embodiments of the present application, but is not intended to limit the scope of the present application, and any such modifications, equivalents and adaptations of the embodiments described above in accordance with the principles of the present application should and are intended to be within the scope of the present application, as long as they do not depart from the scope of the present application.

Claims

1. A touch signal-to-noise ratio increasing circuit, characterized in that the touch signal-to-noise ratio increasing circuit comprises:

2. The touch signal-to-noise ratio increasing circuit of claim 1, further comprising: a first bias capacitor, wherein:

3. The touch signal-to-noise ratio increasing circuit of claim 1, further comprising: a filter, wherein:

4. The touch signal-to-noise ratio increasing circuit of claim 3, further comprising: an analog-to-digital conversion module, wherein:

5. The touch signal-to-noise ratio increasing circuit of claim 1, wherein the first stage operational amplification module is a buffer, the touch signal-to-noise ratio increasing circuit further comprising:

6. The touch signal-to-noise ratio increasing circuit of claim 1, wherein the first stage operational amplification module is a buffer, the touch signal-to-noise ratio increasing circuit further comprising:

7. The touch signal-to-noise ratio increasing circuit of claim 1, wherein the in-phase amplifying module comprises: the in-phase amplifier is connected with the first-stage amplification feedback resistor, the first end of the first-stage amplification feedback resistor is connected with the output end of the in-phase amplifier, and the second end of the first-stage amplification feedback resistor is connected with the inverting input end of the in-phase amplifier.

8. The touch signal-to-noise ratio increasing circuit of claim 7, further comprising:

9. The touch signal-to-noise ratio increasing circuit of claim 8, wherein a gain of the in-phase amplifying module is less than a preset gain threshold.

10. The touch signal-to-noise ratio increasing circuit of claim 1, further comprising: the second-stage non-inverting input resistor, the second-stage inverting input resistor and the second-stage operational amplification module, wherein:

11. The touch signal-to-noise ratio increasing circuit of claim 10, further comprising:

12. The touch signal-to-noise ratio increasing circuit of claim 11, wherein when the first control switch is closed, an in-phase output terminal in the i-th RX path is adjacent to an anti-phase output terminal in the i+1-th RX path; when the second control switch is closed, the opposite phase output end in the ith path RX channel is adjacent to the in-phase output end in the (i+1) path RX channel for difference, and a target difference result is obtained.

13. The touch signal-to-noise ratio increasing circuit of claim 10, wherein the touch sensor further comprises a reference channel; the reference channel comprises: the first offset resistor, the first-stage reverse phase input resistor and the first-stage operational amplification module; wherein the first-stage operational amplification module is an in-phase amplification module,

14. The touch signal-to-noise ratio increasing circuit of claim 13, wherein the second stage in-phase input resistor comprises: a first second-stage in-phase input resistor, a second-stage in-phase input resistor, the second-stage inverting input resistor comprising: a first second-stage inverting input resistor, a second-stage inverting input resistor, wherein:

15. The touch signal-to-noise ratio increasing circuit of claim 10, further comprising a mean value generation channel;

16. The touch signal-to-noise ratio increasing circuit of claim 15, wherein the second stage in-phase input resistor comprises: a first second-stage in-phase input resistor, a second-stage in-phase input resistor, the second-stage inverting input resistor comprising: a first second-stage inverting input resistor and a second-stage inverting input resistor;

17. A capacitive screen comprising the touch signal to noise ratio increasing circuit of any one of claims 1 to 16.

18. A chip comprising the touch signal-to-noise ratio increasing circuit of any one of claims 1-16.

19. An electronic device comprising the chip of claim 18.