A receiver circuit and capacitive pen that resists power frequency interference

Abstract

The present invention discloses a receiving circuit and a capacitive pen capable of resisting power frequency interference. The receiving circuit capable of resisting power frequency interference comprises: a high-pass filtering circuit, the high-pass filtering circuit comprises a charge amplifier circuit and a resistor, a signal input end of the charge amplifier circuit receives a DSSS signal sent by a touch terminal, and is used for charge amplifying and outputting the DSSS signal, and the charge amplifier circuit has a feedback branch; a first end of the resistor is connected to a first end of the feedback branch, and a second end of the resistor is connected to a second end of the feedback branch; a voltage amplifier circuit, an input end of the voltage amplifier circuit is connected to an output end of the charge amplifier circuit, and is used for amplifying and outputting an input voltage; in the present invention, since only the original charge amplifier circuit of the receiving circuit is converted into a capacitive pen capable of resisting power frequency interference by adding a resistor, the volume of the receiving circuit is not greatly changed, so that the power frequency interference is suppressed while the occupation of the internal space of the capacitive pen is reduced as much as possible.

Description

Technical Field

[0001] The present invention relates to the technical field of capacitive pens, and in particular to a receiving circuit and a capacitive pen capable of resisting power frequency interference. Background Art

[0002] At present, capacitive pens are generally powered by batteries and do not need to be grounded. When writing normally, a person's hand must hold the capacitive pen, and as a conductor with a large impedance, the power frequency interference signal can still be transmitted from the human hand to the capacitive pen. The modulated signal normally coupled to the receiving circuit of the capacitive pen is the DSSS modulated signal emitted by the screen, and its frequency range is 50 to 200KHz. The signal voltage coupled to the pen tip is within 1V. The frequency of the power frequency interference signal is generally around 50Hz. When the oscilloscope probe is suspended, a very strong power frequency signal can be measured; when the oscilloscope is used to measure the human body, a power frequency interference signal with a waveform amplitude of tens of volts can also be read from the oscilloscope.

[0003] When the user uses a capacitive stylus, the power frequency interference signal will be transmitted to the capacitive stylus through the user's hand, superimposed with the DSSS signal, and mask the DSSS signal, thereby affecting the capacitive stylus's demodulation of the RX signal. Since the space of the capacitive stylus itself is very tight, it is not suitable to use large integrated devices such as ceramic filters to filter out the power frequency interference signal. Therefore, how to suppress the power frequency interference while minimizing the internal space occupied by the capacitive stylus has become an urgent problem to be solved. Summary of the invention

[0004] The main purpose of the present invention is to provide a capacitive stylus pen that is resistant to power frequency interference, aiming to suppress power frequency interference by using a circuit with a minimum volume.

[0005] To achieve the above object, the present invention provides a receiving circuit capable of resisting power frequency interference, the receiving circuit capable of resisting power frequency interference comprising:

[0006] A charge amplifier circuit, wherein the signal input end of the charge amplifier circuit is used to input a DSSS signal sent by the touch terminal and received by the capacitive stylus, and to charge-amplify the DSSS signal and then output it, and the charge amplifier circuit has a feedback branch;

[0007] A voltage amplifier circuit, the input end of which is connected to the output end of the charge amplifier circuit, and is used to amplify the voltage of the DSSS signal output by the charge amplifier circuit and then output it;

[0008] a resistor, wherein a first end of the resistor is connected to a first end of the feedback branch, and a second end of the resistor is connected to a second end of the feedback branch;

[0009] The resistor is connected in parallel to both ends of the feedback branch of the charge amplifier circuit, and forms a high-pass filter circuit with the charge amplifier circuit, which is used to filter the DSSS signal received by the capacitive pen.

[0010] Optionally, the charge amplification circuit includes a first operational amplifier and a second capacitor;

[0011] The inverting input terminal of the first operational amplifier is the signal input terminal of the charge amplifier circuit, the inverting input terminal of the first operational amplifier is connected to the first terminal of the second capacitor, the non-inverting input terminal of the first operational amplifier is connected to the first DC power supply, the first power supply terminal of the first operational amplifier and the second power supply terminal of the first operational amplifier are respectively connected to the second DC power supply, the output terminal of the first operational amplifier is the signal output terminal of the charge amplifier circuit, the output terminal of the first operational amplifier is connected to the second terminal of the second capacitor, and the ground terminal of the first operational amplifier is grounded.

[0012] Optionally, the voltage amplification circuit includes a second operational amplifier, a second resistor and a third resistor;

[0013] The first end of the second resistor is the input end of the voltage amplifier circuit, the second end of the second resistor is connected to the inverting input end of the second operational amplifier and the first end of the third resistor respectively, the non-inverting input end of the second operational amplifier is connected to the third DC power supply, the first power supply end of the second operational amplifier and the second power supply end of the second operational amplifier are respectively connected to the DC power supply, the output end of the second operational amplifier is the output end of the voltage amplifier circuit, the output end of the second operational amplifier is connected to the first end of the third resistor, and the ground end of the second operational amplifier is grounded.

[0014] Optionally, the receiving circuit for resisting power frequency interference further includes a filtering circuit;

[0015] The input end of the filter circuit is connected to the signal output end of the charge amplifier circuit, and the output end of the filter circuit is connected to the input end of the voltage amplifier circuit, so as to suppress the industrial frequency signal in the DSSS signal output by the charge amplifier circuit;

[0016] Optionally, the filtering circuit is a second capacitor, a first end of the second capacitor is an input end of the filtering circuit, and a second end of the second capacitor is an output end of the filtering circuit.

[0017] The present invention further provides a receiving circuit for resisting power frequency interference, characterized in that the receiving circuit for resisting power frequency interference comprises:

[0018] A charge amplifier circuit, wherein a signal input end of the charge amplifier circuit receives a DSSS signal sent by the touch terminal, and is used to charge-amplify and output the DSSS signal;

[0019] A filter circuit, the input end of which is connected to the signal output end of the charge amplifier circuit, and is used to filter out interference signals;

[0020] A voltage amplifier circuit, the input end of which is connected to the output end of the filter circuit, is used to amplify and output the input voltage.

[0021] The present invention further provides a capacitive stylus pen, characterized in that it comprises the above-mentioned receiving circuit capable of resisting power frequency interference; or comprises the above-mentioned receiving circuit capable of resisting power frequency interference.

[0022] Optionally, the capacitive stylus further includes a demodulation unit;

[0023] The input end of the demodulation unit is connected to the output end of the voltage amplifier circuit, and is used to demodulate the input DSSS signal and output the demodulated signal.

[0024] The technical solution of the present invention is to set a high-pass filter circuit, and on the basis of the original charge amplifier circuit, connect a resistor in parallel to the feedback branch of the charge amplifier circuit, so that the charge amplifier circuit is converted into a high-pass filter circuit, the cut-off frequency of the high-pass filter circuit is negatively correlated with the resistance value of the resistor, and in the high-pass filter circuit, the smaller the resistance value of the resistor, the higher the DSSS signal frequency, the smaller the gain attenuation, so that the low-frequency power frequency signal can be filtered out while the gain attenuation of the high-frequency DSSS signal is small, so as to suppress the power frequency interference; the present invention sets a high-pass filter circuit, so that when the capacitive pen receives the coupled DSSS signal, the gain attenuation of the charge amplifier circuit can be reduced as much as possible while filtering out the high-frequency power frequency signal, so as to solve the problem that when the user uses the capacitive pen, the power frequency signal in the environment is coupled into the receiving circuit of the capacitive pen by the pen tip of the capacitive pen through the human hand and the DSSS signal, thereby submerging the DSSS signal coupled between the screen and the capacitive pen, causing the capacitive pen to malfunction. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying creative work.

[0026] Figure 1 A schematic diagram of a module of an embodiment of a capacitive stylus of the present invention;

[0027] Figure 2 A schematic diagram of a module of an embodiment of a capacitive stylus of the present invention;

[0028] Figure 3 A schematic diagram of the circuit structure of a capacitive stylus according to an embodiment of the present invention;

[0029] Figure 4 The figure is a schematic diagram of the circuit structure of a capacitive stylus according to an embodiment of the present invention.

[0030] Description of Figure Numbers:

[0031] Label name Label name 10 High pass filter circuit V1 Power frequency signal source 11 Charge amplifier circuit U1~U2 First inverting amplifier to second inverting amplifier 12 Resistors C1 Coupler 20 Voltage amplifier circuit C2~C3 Second capacitor to third capacitor 30 Filter circuit R1~R4 First capacitor to fourth capacitor 40 Demodulation circuit

[0032] The realization of the purpose, functional features and advantages of the present invention will be further explained in conjunction with embodiments and with reference to the accompanying drawings. DETAILED DESCRIPTION

[0033] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0034] It should be noted that if the embodiments of the present invention involve directional indications (such as up, down, left, right, front, back, etc.), the directional indications are only used to explain the relative position relationship, movement status, etc. between the components under a certain specific posture (as shown in the accompanying drawings). If the specific posture changes, the directional indication will also change accordingly.

[0035] In addition, if there are descriptions involving "first", "second", etc. in the embodiments of the present invention, the descriptions of "first", "second", etc. are only used for descriptive purposes and cannot be understood as indicating or suggesting their relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In addition, the technical solutions between the various embodiments can be combined with each other, but they must be based on the ability of ordinary technicians in the field to implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be deemed that such a combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0036] The invention provides a receiving circuit capable of resisting power frequency interference and applied to a capacitive stylus.

[0037] Reference Figures 1 to 4 In one embodiment, the high-pass filter circuit 10 includes:

[0038] A charge amplifier circuit 11, wherein the signal input terminal of the charge amplifier circuit 11 is used to input a DSSS signal sent by the touch terminal and received by the capacitive stylus, and to amplify the DSSS signal and then output it, and the charge amplifier circuit 11 has a feedback branch;

[0039] A voltage amplifier circuit 20, the input end of the voltage amplifier circuit 20 is connected to the output end of the charge amplifier circuit 11, and is used to amplify the voltage of the DSSS signal output by the charge amplifier circuit 11 and then output it;

[0040] A resistor 12, wherein a first end of the resistor 12 is connected to a first end of the feedback branch, and a second end of the resistor 12 is connected to a second end of the feedback branch;

[0041] The resistor 12 is connected in parallel to both ends of the feedback branch of the charge amplifier circuit 11 , and together with the charge amplifier circuit 11 forms a high-pass filter circuit 10 for filtering the DSSS signal received by the capacitive pen.

[0042] In this embodiment, when using a capacitive pen, the touch screen terminal can achieve synchronization between the screen and the pen tip and send commands by transmitting a DSSS signal to communicate with the active pen. When using a capacitive pen, a coupling capacitor is formed between the pen tip of the capacitive pen and the terminal screen. The DSSS signal sent by the screen is input into the receiving circuit of the capacitive pen through the coupling between the screen and the pen tip, and is output after amplification by the receiving circuit. The capacitive pen analyzes the amplified DSSS signal to obtain the corresponding DSSS code. The capacitive pen can be an active capacitive pen or a passive capacitive pen. Figure 3 As shown, the coupling capacitor is the first capacitor C1; the DSSS signal is the DSSS signal of the screen coupled to the receiving circuit of the capacitive stylus, and in other embodiments, it may also be other signals that require interference suppression.

[0043] It can be understood that the present invention converts the charge amplifier circuit 11 into a high-pass filter circuit 10 by setting a high-pass filter circuit 10 and connecting a resistor 12 in parallel at both ends of the feedback branch of the charge amplifier circuit 11. The charge amplifier circuit 11 has the ability to charge amplify the DSSS signal. When the charge amplifier circuit 11 is connected in parallel with the resistor at both ends of the feedback branch, the formed capacitor pen 13 for resisting power frequency interference can filter the low-frequency signal and allow the high-frequency signal to pass, and when the high-frequency signal passes through the high-frequency filter circuit 10, the high-frequency signal will be amplified according to the transfer function.

[0044] In the high-frequency filter circuit 10, the cutoff frequency of the high-pass filter circuit 10 is negatively correlated with the resistance value of the first resistor. When the resistance value of the first resistor is smaller, the cutoff frequency of the high-pass filter circuit 10 is larger, and the filtering effect on the low-frequency signal is better. In the high-pass filter circuit 10, when the resistance value of the first resistor R1 is larger, the gain attenuation of the DSSS signal is smaller. Therefore, when the resistance value of the first resistor R1 exceeds a certain range, the DSSS signal will be distorted because the resistance value is too small. By keeping the resistance value of the first resistor R1 within a certain range, the low-frequency power frequency signal can be filtered out while the gain attenuation of the high-frequency DSSS signal is small, thereby suppressing the power frequency interference. The present invention sets a high-pass filter circuit 10 so that when the capacitive pen receives the coupled DSSS signal, the gain attenuation of the charge amplifier circuit 11 can be reduced as much as possible while filtering out the high-frequency power frequency signal. This solves the problem that when the user uses the capacitive pen, the power frequency signal in the environment is coupled into the receiving circuit of the capacitive pen by the tip of the capacitive pen through the human hand and the DSSS signal, thereby drowning the DSSS signal coupled between the screen and the capacitive pen, causing the capacitive pen to malfunction. This realizes the function of suppressing power frequency interference using a circuit with a minimum volume.

[0045] In one embodiment, the charge amplifier circuit 11 includes a first operational amplifier U1, a first capacitor C1 and a second capacitor C2;

[0046] The inverting input terminal of the first operational amplifier U1 is the signal input terminal of the charge amplifier circuit 11, the inverting input terminal of the first operational amplifier U1 is connected to the first terminal of the second capacitor C2, the non-inverting input terminal of the first operational amplifier U1 is connected to the first DC power supply, the first power supply terminal of the first operational amplifier U1 and the second power supply terminal of the first operational amplifier U1 are respectively connected to the second DC power supply, the output terminal of the first operational amplifier U1 is the signal output terminal of the charge amplifier circuit 11, the output terminal of the first operational amplifier U1 is connected to the second terminal of the second capacitor C2, and the ground terminal of the first operational amplifier U1 is grounded.

[0047] In this embodiment, the first DC power supply is a reference voltage, which is used to provide a reference voltage for the charge amplifier circuit 11. When a DSSS signal is input into the charge amplifier circuit 11, the charge amplifier circuit 11 amplifies the DSSS signal based on the reference voltage. The second DC power supply is a capacitor pen power supply voltage. The first power supply terminal of the first operational amplifier U1 and the second power supply terminal of the first operational amplifier U1 are used to power the first operational amplifier U1; the second capacitor C2 is a feedback branch of the charge amplifier circuit 11.

[0048] Specifically, the gain of the charge amplifier circuit 11 is When the DSSS signal is input to the inverting input terminal of the first operational amplifier U1, the first operational amplifier U1 inverts and amplifies the DSSS signal. The transfer function of the high-pass filter circuit 10 is: ω=2πf. It can be seen from the transfer function that when the resistance value of the first resistor R1 is larger, the gain attenuation of the signal is smaller, and the amplification factor of the high-pass filter circuit 10 is closer to the amplification factor of the charge amplifier circuit 11. Therefore, by keeping the resistance value of the first resistor R1 within a certain range, the low-frequency power frequency signal can be suppressed while the gain attenuation of the high-frequency DSSS signal is small, thereby suppressing the power frequency interference; and the cutoff frequency of the high-pass filter circuit 10 is negatively correlated with the resistance value of the first resistor R1. When the resistance value of the first resistor R1 is smaller, the cutoff frequency of the high-pass filter circuit 10 is larger, and the filtering effect on the low-frequency signal is better. When the resistance value of the first resistor R1 exceeds a certain range, the DSSS signal will be distorted because the resistance value is too small. Therefore, by keeping the resistance value of the first resistor R1 within a certain range, the high-pass filter circuit 10 can reduce the gain attenuation of the charge amplifier circuit 11 as much as possible while filtering out the high-frequency industrial frequency signal, thereby solving the problem that when a user uses a capacitive pen, the industrial frequency signal in the environment is coupled into the receiving circuit of the capacitive pen by the tip of the capacitive pen through the human hand and the DSSS signal, thereby drowning the DSSS signal coupled between the screen and the capacitive pen, causing the capacitive pen to malfunction, thereby realizing the function of suppressing industrial frequency interference using a circuit with a minimum volume.

[0049] Reference Figure 1 and Figure 3 In one embodiment, the voltage amplifier circuit 20 includes a second operational amplifier U2, a second resistor R2 and a third resistor R3;

[0050] The first end of the second resistor R2 is the input end of the voltage amplifier circuit 20, the second end of the second resistor R2 is respectively connected to the inverting input end of the second operational amplifier U2 and the first end of the third resistor R3, the non-inverting input end of the second operational amplifier U2 is connected to the third DC power supply, the first power supply end of the second operational amplifier U2 and the second power supply end of the second operational amplifier U2 are respectively connected to the fourth DC power supply, the output end of the second operational amplifier U2 is the output end of the voltage amplifier circuit 20, the output end of the second operational amplifier U2 is connected to the first end of the third resistor R3, and the ground end of the second operational amplifier U2 is grounded.

[0051] In this embodiment, the third DC power supply and the first DC power supply are the same reference power supply, which is used to provide a reference voltage for the voltage amplifier circuit 20. When the DSSS signal amplified by the charge amplifier circuit 11 is input into the voltage amplifier circuit 20, the voltage amplifier circuit 20 amplifies the DSSS signal based on the reference voltage. The fourth DC power supply and the second DC power supply are the same power supply, which is used to power the second operational amplifier U2.

[0052] When the user uses a capacitive stylus, the DSSS signal is coupled to the tip of the capacitive stylus through the screen and input to the high-pass filter circuit 10. The high-pass filter circuit 10 performs low-frequency filtering on the DSSS signal and amplifies the input DSSS signal to convert the input DSSS signal from a weak charge into a larger voltage output. The voltage amplifier circuit 30 performs secondary amplification on the input voltage through the second inverting amplifier U2 and outputs it. The voltage amplification gain of the voltage amplifier circuit 30 is Therefore, the capacitive stylus can eliminate the interference of the power frequency signal when receiving the DSSS signal.

[0053] The voltage amplifier circuit 30 performs secondary amplification on the input voltage according to its transfer function, so that the output end of the voltage amplifier circuit 30 outputs the amplified DSSS signal, and the input DSSS signal is converted from a weak charge amount into a voltage output that can be demodulated by a subsequent circuit. Therefore, by setting the voltage amplifier circuit 30, the capacitive pen can suppress the interference of the DSSS signal interfered by the low-frequency power frequency signal when being used, and filter out the power frequency signal, so that the capacitive pen can accurately demodulate the DSSS signal.

[0054] In the capacitive stylus, only the original charge amplifier circuit 11 of the receiving circuit is converted into a high-pass filter circuit 10 by adding a resistor 12, and the volume of the receiving circuit is not greatly changed. Therefore, the minimum volume circuit is used for the capacitive stylus to suppress power frequency interference.

[0055] Reference Figure 1 and Figure 3 In one embodiment, the capacitive stylus further includes a filter circuit 30;

[0056] The input end of the filter circuit 30 is connected to the output end of the high-pass filter circuit 10 , and the output end of the filter circuit 30 is connected to the input end of the voltage amplifier circuit 30 , so as to suppress the industrial frequency signal in the DSSS signal output by the charge amplifier circuit.

[0057] In this embodiment, the filter circuit 30 is a second capacitor C2 , a first end of the second capacitor C2 is an input end of the filter circuit 30 , and a second end of the second capacitor C2 is an output end of the filter circuit 30 .

[0058] Specifically, after the DSSS signal is low-frequency filtered by the high-pass filter circuit 10, there is still a small amount of low-frequency clutter interference. The clutter that is not filtered out will interfere with the demodulation process of the DSSS signal when the user uses the capacitive pen, so that after the tip of the capacitive pen captures the DSSS signal sent by the screen, the DSSS signal is submerged by the power frequency signal, so that the capacitive pen cannot accurately demodulate the signal. Therefore, in order to enable the capacitive pen to accurately receive the instruction sent by the terminal, it is necessary to perform secondary filtering on the input voltage, that is, the input information after charge amplification and power frequency suppression, so as to obtain a pure DSSS signal. Therefore, it is necessary to perform secondary filtering on the input voltage. Since only the filter circuit 30 that realizes a simple function, that is, the second capacitor C2, is added to the capacitive pen, the circuit that receives the DSSS signal by the capacitive pen is not greatly changed in volume, so it is realized that the capacitive pen uses a minimum volume circuit to suppress power frequency interference.

[0059] The invention also provides a receiving circuit capable of resisting power frequency interference, which is applied to a capacitive stylus.

[0060] Reference Figure 2 and Figure 3 In one embodiment, the receiving circuit for resisting power frequency interference includes:

[0061] A charge amplifier circuit 11, wherein a signal input end of the charge amplifier circuit 11 receives a DSSS signal sent by a terminal, and is used to charge-amplify and output the DSSS signal;

[0062] A filter circuit 30, the input end of the filter circuit 30 is connected to the signal output end of the charge amplifier circuit 11, and is used to filter out interference signals;

[0063] The voltage amplifier circuit 20 has an input end connected to the output end of the filter circuit 30 and is used to amplify and output the input voltage.

[0064] In this embodiment, when using a capacitive pen, the touch screen terminal can achieve synchronization between the screen and the pen tip and send commands by transmitting a DSSS signal to communicate with the active pen. When using a capacitive pen, a coupling capacitor is formed between the pen tip of the capacitive pen and the terminal screen, and the DSSS signal sent by the screen is input into the receiving circuit of the capacitive pen through the coupling between the screen and the pen tip, and is output after amplification by the receiving circuit. The capacitive pen analyzes the amplified DSSS signal to obtain the corresponding DSSS code. The capacitive pen can be an active capacitive pen or a passive capacitive pen, or other smart pens such as a touch pen; the coupling capacitor is the first capacitor C1; the DSSS signal is the DSSS signal of the screen coupled to the receiving circuit of the capacitive pen, and in other embodiments, it can also be other signals that need to be interfered with.

[0065] The filter circuit 30 is a second capacitor C2 , a first end of the second capacitor C2 is an input end of the filter circuit 30 , and a second end of the second capacitor C2 is an output end of the filter circuit 30 .

[0066] Specifically, the present invention sets a filter circuit 30, and the charge amplifier circuit 11 has the ability to charge amplify the DSSS signal. When the DSSS signal is input into the charge amplifier circuit 11, the input weak charge is amplified into a larger voltage. After the DSSS signal is charge amplified by the charge amplifier circuit 11, the power frequency signal in the air is transmitted into the receiving circuit of the capacitive pen through the human hand. The DSSS signal is interfered by the power frequency signal, which will interfere with the demodulation process of the DSSS signal when the user uses the capacitive pen. After the tip of the capacitive pen captures the DSSS signal sent by the screen, the DSSS signal is submerged by the power frequency signal, so that the capacitive pen cannot accurately demodulate the signal. Therefore, in order for the capacitive pen to accurately receive the command sent by the terminal, it is necessary to filter the input voltage, that is, the DSSS signal passing through the charge amplifier circuit 11, so as to obtain a pure DSSS signal.

[0067] The voltage amplifier circuit 30 performs secondary amplification on the input voltage according to its gain, so that the output end of the voltage amplifier circuit 30 outputs the amplified DSSS signal, and converts the input DSSS signal from a weak charge amount into a voltage output that can be demodulated by subsequent circuits.

[0068] In the capacitive stylus, only the filtering circuit 30, i.e., the third capacitor C3, is added between the charge amplifier circuit 11 and the voltage amplifier circuit 20 of the receiving circuit, and the volume of the receiving circuit is not significantly changed. Therefore, the minimum volume circuit is used for the capacitive stylus to suppress power frequency interference.

[0069] The invention also provides a capacitive stylus.

[0070] Reference Figure 1 and Figure 3 In one embodiment, it includes a receiving circuit that is resistant to power frequency interference; or, it includes another receiving circuit that is resistant to power frequency interference.

[0071] The capacitive stylus further includes a demodulation unit 40;

[0072] The input end of the demodulation unit 40 is connected to the output end of the voltage amplifier circuit 20 , and is used to demodulate the input DSSS signal and output the demodulated signal.

[0073] In this embodiment, when using a capacitive pen, a coupling capacitor is formed between the tip of the capacitive pen and the terminal screen. The tip of the capacitive pen can accurately capture tiny screen charges for coupling, obtain a DSSS signal, and output the DSSS signal. The DSSS signal is obtained by coupling the receiving circuit of the capacitive pen with the screen.

[0074] Specifically, when the user is using the capacitive pen, the DSSS signal is coupled to the coupling module 20 through the screen and input into the high-pass filter circuit 10. When passing through the high-pass filter circuit 10, the high-pass filter circuit 10 performs low-frequency filtering on the DSSS signal, and amplifies the input DSSS signal by charge, so that the input DSSS signal is converted from a weak charge to a larger voltage output. The voltage amplifier circuit 30 performs secondary amplification on the input voltage and outputs it, so that the capacitive pen can eliminate the interference of the power frequency signal and smoothly demodulate the DSSS signal. The demodulation unit 40 demodulates the execution signal according to the input DSSS signal, and outputs it to the control part of the capacitive pen to control the capacitive pen to work. Since the power frequency signal introduced from the environment and the human body is filtered out during the process of receiving the DSSS signal, the capacitive pen can eliminate interference and accurately demodulate the DSSS signal when working. In addition, since in the capacitive pen, only the original charge amplifier circuit 11 of the receiving circuit is converted into the high-pass filter circuit 10 by adding a resistor 12, and the volume of the receiving circuit is not greatly changed, it is realized that the capacitive pen uses the minimum volume circuit to suppress the power frequency interference.

[0075] The above descriptions are only optional embodiments of the present invention, and are not intended to limit the patent scope of the present invention. All equivalent structural changes made using the contents of the present invention's specification and drawings, or directly / indirectly applied in other related technical fields, are included in the patent protection scope of the present invention.

Claims

1. A receiving circuit resistant to power frequency interference, used for a capacitive stylus pen, characterized in that: The receiving circuit for resisting power frequency interference comprises: A charge amplifier circuit, wherein the signal input end of the charge amplifier circuit is used to input a DSSS signal sent by the touch terminal and received by the capacitive stylus, and to charge-amplify the DSSS signal and then output it, and the charge amplifier circuit has a feedback branch; A voltage amplifier circuit, the input end of which is connected to the output end of the charge amplifier circuit, and is used to amplify the voltage of the DSSS signal output by the charge amplifier circuit and then output it; a resistor, wherein a first end of the resistor is connected to a first end of the feedback branch, and a second end of the resistor is connected to a second end of the feedback branch; The resistor is connected in parallel to both ends of the feedback branch of the charge amplifier circuit, and forms a high-pass filter circuit with the charge amplifier circuit, which is used to filter the DSSS signal received by the capacitive pen; The high-pass filter circuit is used for filtering the low-frequency signal to allow the DSSS signal to pass; and for amplifying the DSSS signal according to a transfer function.

2. The receiving circuit for resisting power frequency interference as claimed in claim 1, characterized in that: The charge amplification circuit includes a first operational amplifier and a second capacitor; The inverting input terminal of the first operational amplifier is the signal input terminal of the charge amplifier circuit, the inverting input terminal of the first operational amplifier is connected to the first terminal of the second capacitor, the non-inverting input terminal of the first operational amplifier is connected to the first DC power supply, the first power supply terminal of the first operational amplifier and the second power supply terminal of the first operational amplifier are respectively connected to the second DC power supply, the output terminal of the first operational amplifier is the signal output terminal of the charge amplifier circuit, the output terminal of the first operational amplifier is connected to the second terminal of the second capacitor, and the ground terminal of the first operational amplifier is grounded.

3. The receiving circuit for resisting power frequency interference as claimed in claim 1, characterized in that: The voltage amplification circuit includes a second operational amplifier, a second resistor and a third resistor; The first end of the second resistor is the input end of the voltage amplifier circuit, the second end of the second resistor is connected to the inverting input end of the second operational amplifier and the first end of the third resistor respectively, the non-inverting input end of the second operational amplifier is connected to the third DC power supply, the first power supply end of the second operational amplifier and the second power supply end of the second operational amplifier are connected to the fourth DC power supply respectively, the output end of the second operational amplifier is the output end of the voltage amplifier circuit, the output end of the second operational amplifier is connected to the first end of the third resistor, and the ground end of the second operational amplifier is grounded.

4. The receiving circuit for resisting power frequency interference as claimed in claim 1, characterized in that: The receiving circuit for resisting power frequency interference also includes a filtering circuit; The input end of the filter circuit is connected to the signal output end of the charge amplifier circuit, and the output end of the filter circuit is connected to the input end of the voltage amplifier circuit, so as to suppress the industrial frequency signal in the DSSS signal output by the charge amplifier circuit.

5. The receiving circuit for resisting power frequency interference as claimed in claim 4, characterized in that: The filtering circuit is a second capacitor, a first end of the second capacitor is an input end of the filtering circuit, and a second end of the second capacitor is an output end of the filtering circuit.

6. A capacitive stylus pen, characterized in that: The invention comprises a receiving circuit capable of resisting power frequency interference as described in any one of claims 1 to 5.

7. The capacitive stylus pen according to claim 6, characterized in that: The capacitive stylus further includes a demodulation unit; The input end of the demodulation unit is connected to the output end of the voltage amplifier circuit, and is used to demodulate the input DSSS signal and output the demodulated signal.

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