阅读说明：本技术 基于互电容触摸屏的电荷放大器及稳定波形输出方法 (Charge amplifier based on mutual capacitance touch screen and stable waveform output method ) 是由 文钧 于 2020-12-18 设计创作，主要内容包括：本发明公开一种提供基于互电容触摸屏的电荷放大器及稳定波形输出方法,包括：前置放大器、反馈电容C-f、第一反馈电阻Rf1、第二反馈电阻Rf2和开关S1,所述前置放大器的负相输入端连接屏体组件,正相输入端接收参考电压,所述第一反馈电阻Rf1与第二反馈电阻Rf2串联,并连接在前置放大器的负相输入端和正相输入端之间,所述反馈电容C-f并联在串联的第一反馈电阻Rf1和第二反馈电阻Rf2之间,所述开关S1并联在所述第二反馈电阻Rf2两端,所述第二反馈电阻Rf1阻值小于所述第二反馈电阻Rf2的阻值；本发明所述的电路可以使得电荷放大器快速稳定,从而改善输出波形,使放大器工作稳定,工作频率加宽。(The invention discloses a charge amplifier based on a mutual capacitance touch screen and a stable waveform output method, which comprises the following steps: preamplifier and feedback capacitor C f The preamplifier comprises a first feedback resistor Rf1, a second feedback resistor Rf2 and a switch S1, wherein the negative phase input end of the preamplifier is connected with a screen body assembly, the positive phase input end of the preamplifier receives a reference voltage, the first feedback resistor Rf1 is connected with the second feedback resistor Rf2 in series and is connected between the negative phase input end and the positive phase input end of the preamplifier, and the feedback capacitor C f The switch S1 is connected in parallel between the first feedback resistor Rf1 and the second feedback resistor Rf2 which are connected in series, the resistance value of the second feedback resistor Rf1 is smaller than that of the second feedback resistor Rf 2; the circuit of the invention can make the charge amplifier quickly stable, thereby improving the output waveform, making the amplifier work stably and widening the working frequency.)

1. A mutual capacitance touch screen based charge amplifier, comprising: preamplifier and feedback capacitor C_fThe preamplifier comprises a first feedback resistor Rf1, a second feedback resistor Rf2 and a switch S1, wherein the negative phase input end of the preamplifier is connected with a screen body assembly, the positive phase input end of the preamplifier receives a reference voltage, the first feedback resistor Rf1 is connected with the second feedback resistor Rf2 in series and is connected between the negative phase input end and the positive phase input end of the preamplifier, and the feedback capacitor C_fThe switch S1 is connected in parallel between the first feedback resistor Rf1 and the second feedback resistor Rf2 which are connected in series, the switch S1 is connected in parallel at two ends of the second feedback resistor Rf2, and the resistance value of the second feedback resistor Rf1 is smaller than that of the second feedback resistor Rf2The resistance of the feedback resistor Rf 2.

2. The mutual capacitance touch screen-based charge amplifier of claim 1, wherein the screen assembly comprises a screen capacitance C_sAnd screen body resistance R_sSaid screen body capacitance C_sOne end is connected with the signal transmitting end, and the other end is connected with the screen resistor R_sConnected, screen body resistance R_sAnd is connected with the negative phase input end of the preamplifier.

3. The mutual capacitance touch screen-based charge amplifier of claim 2, wherein the sum R of the resistances of the first feedback resistor Rf1 and the second feedback resistor Rf2_fExpressed as:

further, it is possible to prevent the occurrence of,

wherein Vout is the output voltage of the preamplifier, Vin is the input voltage value, and | | is the parallel symbol.

4. The mutual capacitance touch screen-based charge amplifier of claim 3, wherein R is_fDivided into n parts, so that each part has a resistance value ofWherein n is more than or equal to 3 and n is a positive integer, and the resistance value of the first feedback resistor is divided as follows according to the requirement:

the resistance of the second feedback resistor is:

wherein i < n/2 and i is a positive integer.

5. The mutual capacitance touch screen-based charge amplifier of claim 2, wherein the feedback capacitance C is_fThe values of (d) are expressed as:

vout is the output voltage of the preamplifier, and Vin is the input voltage value.

6. The method for outputting the stable waveform realized by the charge amplifier based on the mutual capacitance touch screen according to any one of claims 2 to 5, is characterized by comprising the following steps:

step 1, determining screen capacitance C_sCapacitance and screen resistance R_sThe resistance value of (1);

step 2, determining feedback capacitor C_fValue of (D) and feedback resistance R_fThe resistance value of (1);

step 3, starting the circuit, closing the switch S1 and feeding back the capacitor C to be fed back_fAfter the charging and discharging are finished and the circuit is stabilized, the switch S1 is switched off, and the corresponding output waveform is obtained after the output of the preamplifier is stabilized.

Technical Field

The invention relates to the technical field of charging circuits, in particular to a charge amplifier based on a mutual capacitance touch screen and a stable waveform output method.

Background

As is well known, an electronic system with touch sensing function includes a touch area for a user to touch with a finger or a stylus. The capacitive touch technology is mostly used in touch screens with medium and small sizes, and becomes the mainstream technology with the largest application amount in the market.

A touch screen using capacitive touch technology generally includes a touch panel superimposed on the screen for a user to touch with his or her hand or a touch pen, wherein the touch panel includes a plurality of wires each coupled to a touch sensing circuit in a touch sensing device.

Capacitive touch technologies are mainly classified into two types, one is a self-capacitive touch technology, and the other is a mutual capacitive touch technology. Both techniques rely on the change in capacitance on a wire when a finger or stylus is brought close to the wire of the touch pad, and the position of the touch point is known by measuring the voltage drop of the driving potential. The mutual capacitance induction type touch screen comprises a plurality of driving lines and a plurality of induction lines, wherein the driving lines and the induction lines are arranged in a crossed mode, and mutual capacitance is formed at the crossed position of the driving lines and the induction lines. Mutual capacitance induction touch screens can include mutual capacitances arranged in an array.

If the existing charge amplifier has no feedback resistor, the direct current amplifier can be considered to be infinite, and then the operational amplifier is slightly maladjusted, so that the output level is at the power supply voltage or 0 level; if there is a feedback resistor, but the feedback resistor is extremely small, the output waveform is most likely to be clipped and distorted if the input is square wave, and the K value is extremely large if the crest distortion degree is a slope K, as shown in fig. 1; if there is a feedback resistor, and the feedback resistor is very large, it will take a long time for the output waveform to stabilize if the input is square wave, and if the peak distortion is slope K ', the value of K' is very small and can approach 0 infinitely, as shown in fig. 2. Therefore, the whole touch area is unstable in operation and slow in response speed.

Disclosure of Invention

The purpose of the invention is as follows: in order to overcome the defects of the prior art, the invention provides a charge amplifier based on a mutual capacitance touch screen, which can solve the problems of poor stability or poor quality of output waveforms, and also provides a stable waveform output method.

The technical scheme is as follows: one aspect of the present invention provides a charge amplifier based on a mutual capacitance touch screen, including: preamplifier and feedback capacitor C_fA first feedback resistor Rf1, a second feedback resistor Rf2 and a switch S1, the pre-amplificationThe negative phase input end of the amplifier is connected with the screen body assembly, the positive phase input end of the amplifier receives a reference voltage, the first feedback resistor Rf1 is connected with the second feedback resistor Rf2 in series and connected between the negative phase input end and the positive phase input end of the preamplifier, and the feedback capacitor C_fThe switch S1 is connected in parallel between the first feedback resistor Rf1 and the second feedback resistor Rf2 which are connected in series, the resistance of the second feedback resistor Rf1 is smaller than that of the second feedback resistor Rf 2.

Further, the method comprises the following steps:

the screen assembly comprises a screen capacitor C_sAnd screen body resistance R_sSaid screen body capacitance C_sOne end is connected with the signal transmitting end, and the other end is connected with the screen resistor R_sConnected, screen body resistance R_sAnd is connected with the negative phase input end of the preamplifier.

Further, the method comprises the following steps:

sum R of resistance values of the first feedback resistor Rf1 and the second feedback resistor Rf2_fExpressed as:

further, it is possible to prevent the occurrence of,

wherein Vout is the output voltage of the preamplifier, Vin is the input voltage value, and | | is the parallel symbol.

Further, the method comprises the following steps:

r is to be_fDivided into n parts, so that each part has a resistance ofWherein n is more than or equal to 3 and n is a positive integer, and the resistance value of the first feedback resistor is divided as follows according to the requirement:

the resistance of the second feedback resistor is:

wherein i < n/2 and i is a positive integer.

Further, the method comprises the following steps:

feedback capacitance C_fThe values of (d) are expressed as:

vout is the output voltage of the preamplifier, and Vin is the input voltage value.

On the other hand, the invention also provides a charging and discharging method realized by the charging circuit based on the mutual capacitance touch screen, which comprises the following steps:

step 1, determining screen capacitance C_sCapacitance and screen resistance R_sThe resistance value of (1);

step 2, determining feedback capacitor C_fValue of (D) and feedback resistance R_fThe resistance value of (1);

step 3, starting the circuit, closing the switch S1 and feeding back the capacitor C to be fed back_fAfter the charging and discharging are finished and the circuit is stabilized, the switch S1 is switched off, and the corresponding output waveform is obtained after the output of the preamplifier is stabilized.

Has the advantages that: (1) the circuit of the invention can lead the charge amplifier to be fast and stable, thereby improving the output waveform, leading the amplifier to work stably and leading the working frequency to be widened; (2) the circuit of the invention has wide application range, and can be applied to any capacitive touch screen or preamplifier related to the capacitive touch screen.

Drawings

FIG. 1 is a schematic diagram illustrating a comparison between an input square wave and an output waveform of a charge amplifier when a feedback resistor is too small in the prior art;

FIG. 2 is a schematic diagram illustrating a comparison between an input square wave and an output waveform of a charge amplifier when a feedback resistor is too large in the prior art;

FIG. 3 is a circuit diagram of a charge amplifier according to an embodiment of the present invention;

fig. 4 is a schematic diagram comparing the input square wave and the output waveform of the charge amplifier according to the embodiment of the invention.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

As shown in fig. 3, the present invention provides a charge amplifier based on a mutual capacitance touch screen, including: preamplifier and feedback capacitor C_fThe preamplifier comprises a first feedback resistor Rf1, a second feedback resistor Rf2 and a switch S1, wherein the negative phase input end of the preamplifier is connected with a screen body assembly, the positive phase input end of the preamplifier receives a reference voltage, the first feedback resistor Rf1 is connected with the second feedback resistor Rf2 in series and is connected between the negative phase input end and the positive phase input end of the preamplifier, and a feedback capacitor C_fThe switch S1 is connected in parallel between the first feedback resistor Rf1 and the second feedback resistor Rf2 which are connected in series, the switch S1 is connected in parallel at two ends of the second feedback resistor Rf2, and the resistance value of the second feedback resistor Rf1 is smaller than that of the second feedback resistor Rf 2.

The output signal generated by the preamplifier is detected in a detection circuit to judge whether touch occurs or not, the output signal of the detection circuit is reset to a reference level before the edge of the pulse signal changes, and the phase clock of the detection circuit and the phase clock of the transmitting end are kept synchronous.

A preamplifier circuit is actually one specific application of an integrating circuit. The preamplifier circuit may perform an integration process on the received charge signal to generate a corresponding voltage signal. The smaller the capacitance value of the integrating capacitor of the preamplifier circuit, the larger the output voltage is, and the larger the gain is, whereas the larger the capacitance value of the integrating capacitor is, the smaller the output voltage is, and the smaller the gain can be far smaller than the input.

The feedback resistor sets a closed loop dynamic range, simultaneously influences the bandwidth and the stability, increases the value of the feedback resistor and can achieve stable bias current. Based on the application of the feedback resistor, the current feedback device has very high slew rate and adjustable bandwidth, and the current feedback device has the greatest advantage of very good large signal bandwidth, so that the large signal bandwidth of the device is very close to the small signal bandwidth. Moreover, due to the inherent linearity, low distortion is obtained even for large signals at high frequencies.

Based on the above, the main improvements of the present invention are: the resistance value of the feedback resistor connected into the circuit is controlled through the switch, a small feedback resistor is connected into the circuit, after the circuit is started, the output result of the preamplifier can be quickly stabilized, obvious topping distortion can occur to the output result, then the control switch is opened, the feedback resistor with the larger resistance value is connected in series, the series connection increasing feedback resistor can improve the output waveform, the amplifier is stable in work, and the working frequency is widened.

Wherein the screen assembly comprises a screen capacitor C_sAnd screen body resistance R_sScreen body capacitance C_sOne end of the resistor is connected with a signal transmitting end, square wave signals are input, and the other end of the resistor is connected with a screen resistor R_sConnected, screen body resistance R_sAnd is connected with the negative phase input end of the preamplifier.

And the sum R of the resistances of the first feedback resistor Rf1 and the second feedback resistor Rf2_fCalculated according to the user's requirements and circuit structure, i.e. the feedback resistance R_fThe feedback resistor Rf1 and the feedback resistor Rf2 are divided into two parts, namely a small feedback resistor Rf1 is connected firstly, the feedback resistor Rf2 is connected with a closed switch in parallel to enable the output of the preamplifier to be rapidly stabilized, the switch is disconnected after the result is stabilized, a large feedback resistor Rf2 is connected in series, and the output of the preamplifier can be rapidly stabilized after the feedback resistor Rf2 is connected in series because the previous output is stabilizedAnd the output waveform and the bandwidth can be improved.

Firstly, determining the capacitance C of the screen body according to the user's requirement_sA value of (d); determining a screen resistance R related to said screen capacitance_sA value of (d); determining a feedback capacitance C_fThe value of (c): since the output of the preamplifier needs to be less than the signal emitted by the input in a touch system, in this case, the input resistor R can be ignored according to the specific output requirements when determining the feedback capacitance_sAnd a feedback resistor R_fA coarse calculation is performed. According to the formulaThus, the feedback capacitance C can be estimated preliminarily_fThe capacity value of (c), namely:

vout is the output voltage of the preamplifier, and Vin is the input voltage value.

Next, the sum R of the resistances of the first feedback resistor Rf1 and the second feedback resistor Rf2 is determined_fThe value of (c):

the method can be adopted: (1) determining the charge and discharge variation of the preamplifier according to the design requirement, calculating the charge and discharge time according to the variation and the input signal period, and calculating the feedback resistance R through the calculation of the charge and discharge of the capacitor_fThe resistance value of (c). Under the condition that the time for the output to reach the stabilizing device and the variation quantity meet the requirements, the calculated feedback resistance R can be verified through simulation_fThe resistance value of (c).

Method (2) may also be employed: according to the formulaAnd a screen body resistance R_sScreen body capacitance C_sFeedback capacitance C_fAre of known quantity and, furthermore,

wherein Vout is the output voltage of the preamplifier, Vin is the input voltage value, and | | is the parallel symbol. And the resistance value can be verified by simulation.

R is to be_fDivided into n parts, so that each part has a resistance ofWherein n is more than or equal to 3 and n is a positive integer, and the resistance value of the first feedback resistor is divided as follows according to the requirement:

the resistance of the second feedback resistor is:

wherein i < n/2 and i is a positive integer.

When the circuit is started, the resistors are divided according to the requirements of a designer, only the divided relatively small feedback resistor Rf1 is accessed in the initial stage to enable the circuit to be quickly started and reach a stable state, then the other feedback resistor Rf2 is accessed, and due to different requirements of the designer, the specific resistance value of the first feedback resistor is different, simulation can be carried out within the set range of the first feedback resistor, and the purpose of outputting the optimal waveform is achieved, as shown in FIG. 3.

On the basis of the circuit, the invention also provides a stable waveform output method realized based on the charge amplifier of the mutual capacitance touch screen, which comprises the following steps:

step 1, determining screen capacitance C_sCapacitance and screen resistance R_sThe resistance value of (1);

step 2, determining feedback capacitor C_fValue of (D) and feedback resistance R_fThe resistance value of (1);

step 3, starting the circuit, closing the switch S1,capacitor C to be fed back_fAnd finishing charging and discharging.

The switch S1 is closed, the feedback resistor Rf2 is shielded, and the feedback capacitor C is connected_fThe charge and discharge speed of the battery is very fast, so the battery can be stabilized in a very fast time.

And 4, turning off the switch S1, and obtaining a corresponding output waveform after the output of the preamplifier is stable.

After the first stage is completed, as shown in fig. 4, the switch S1 is turned off at a certain rising edge of the input square wave signal, and the feedback resistor Rf1 and the feedback resistor Rf2 are connected in series, so that the output of the charge amplifier can be stabilized quickly in this case because the circuit is already started and stable, and the charge on the holding capacitor after stabilization is not easily discharged due to the large feedback resistor, and the discharge slope K' is small, so as to reach the state required by the designer. Therefore, the invention can rapidly stabilize the output waveform of the charge amplifier. The circuit has wide application range, and the technology can be suitable for any capacitive touch screen or a preamplifier related to the capacitive touch screen.

It will be apparent to those skilled in the art that various modifications and variations can be made in the embodiments of the present invention without departing from the spirit or scope of the embodiments of the invention. Thus, if such modifications and variations of the embodiments of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to encompass such modifications and variations.