CN104577328B - A kind of RFID antenna and its automatic matching method - Google Patents

Abstract

The invention relates to an RFID antenna and an automatic matching method thereof, comprising a coaxial feeder, a balun, a load modulation transistor, a load modulation resistor, a parallel matching capacitor group, a series matching capacitor group, an antenna metal tube, a Q value adjusting resistor, and a control circuit , microcontroller, drive circuit, detection circuit, analog-to-digital converter ADC, and the automatic matching method includes: (1) measuring user RFID antenna parameters; (3) control the access of the matching capacitor; (4) fine-tune the matching point. Users do not need to change the circuit and RFID reader, install RFID readers of different shapes, which are suitable for different applications, so that the RFID antenna can basically achieve the best matching state, and can also change the parameters of the matching circuit when the parameters of the RFID reader change, to achieve Automatic matching, guaranteed bandwidth and economical practicability.

Description

An RFID antenna and its automatic matching method

technical field

The invention relates to an RFID antenna and an automatic matching method thereof, belonging to the field of electricity.

Background technique

Radio Frequency Identification (RFID) is a non-contact automatic identification technology. It automatically identifies the target object and obtains relevant data through radio frequency signals. The identification work does not require manual intervention. As a wireless version of barcodes, RFID technology has waterproof properties that barcodes do not have. , antimagnetic, high temperature resistance, long service life, large reading distance, data on the label can be encrypted, storage data capacity is larger, storage information can be changed freely, etc. Its application will bring revolutionary changes to retail, logistics and other industries.

The RFID system is composed of three parts: reader, electronic tag and application software. Its working principle is that the reader emits a wireless electromagnetic wave of a specific frequency to drive the electronic tag to send its internal data. At this time, the reader receives and interprets the data , sent to the application for corresponding processing.

At present, RFID systems based on the ISO15693 protocol and ISO14443 protocol are widely used in China. Their working center frequency is 13.56MHz and they work in a passive manner. This requires the reader to have a good impedance matching of the transmitting antenna to ensure that it can transmit enough power. The antennas of the RFID system that can be seen in the domestic market are all fixed matching modes, mainly squares of different sizes. The matching circuit is also fixed at the factory. Users cannot bend or change the shape of the antenna, otherwise it will cause standing waves in the antenna. increase, efficiency decline or even damage to equipment. In practical applications, some occasions require the user to change the form of the antenna, such as strip shape, circular shape, or other even integrated with decorations. To support this function, it is necessary to provide an antenna impedance automatic detection and method of matching.

Contents of the invention

Aiming at the deficiencies of the prior art, the present invention discloses an RFID antenna;

The invention also discloses an automatic matching method for the RFID antenna;

The principle of the automatic matching method of the above-mentioned RFID antenna is as follows: First, measure the inherent series inductance L0 and the inherent series resistance R0, and then, according to the calculation formula of the LC matching circuit, obtain the parallel matching capacitance Cp that should be connected to the circuit and the value Cp that should be connected to the circuit. The capacitance value Cs is matched in series, and then the microcontroller selects the closest capacitance value through the magnetic latching relay to connect to the circuit, and finally, fine-tuning is performed.

Technical scheme of the present invention is:

An RFID antenna, including a coaxial feeder, a balun, a load modulation triode, a load modulation resistor, a parallel matching capacitor group, a series matching capacitor group, an antenna metal tube, a Q value adjusting resistor, a control circuit, a microcontroller, a driving circuit, The detection circuit and the analog-to-digital converter ADC, the parallel matching capacitor group includes multiple parallel-connected parallel matching capacitors and magnetic latching relays, and the series matching capacitor group includes multiple series-connected series matching capacitors and magnetic latching relays, so The antenna metal tube includes an inherent series inductance L0 and an inherent series resistance R0, the coaxial feeder is connected to the input end of the balun, the output end of the balun is connected to the parallel matching capacitor group, and the output end of the balun is simultaneously One end of the series matching capacitor group is connected, the other end of the series matching capacitor group is connected in series with one end of the antenna metal tube, the other end of the antenna metal tube is connected in series with the Q value adjusting resistor, and the Q value adjusting resistor is connected to the The balun output terminal; the balun output terminal is also connected to the input terminal of the detection circuit, the output terminal of the detection circuit is connected to the analog-to-digital converter ADC, and the analog-to-digital converter ADC is connected to the microcontroller One output control signal of the microcontroller is connected to the drive circuit, the drive circuit is connected to the control terminals of each magnetic latching relay through the control line, and the other output control signal of the microcontroller is connected to To the base of the load modulation transistor, the emitter and collector of the load modulation transistor are connected in parallel with the output terminal of the balun through the load modulation resistor.

Preferably, according to the present invention, the capacitance values of the multiple parallel matching capacitors in the parallel matching capacitor group are 2 times from small to large, and the capacitance values of the multiple series matching capacitors in the series matching capacitor group are from small to large. 2x relationship.

The capacitance values of a plurality of parallel matching capacitors in the parallel matching capacitor group are doubled from small to large, for example, the capacitance values of the seven parallel matching capacitors in the parallel matching capacitor group are 25p, 50p, 100p, 200p, 400p, 800p, 1600p; the capacitance value of multiple series matching capacitors in the series matching capacitor group is 2 times from small to large, for example, the capacitance value of ten series matching capacitors in the series matching capacitor group The order is 1p, 2p, 4p, 8p, 16p, 32p, 64p, 128p, 256p, 512p.

The antenna metal tube is bent and replaced by the user. The main parameters of the antenna metal tube are equivalent to the inherent series inductance L0 and the inherent series resistance R0.

The automatic matching method of above-mentioned RFID antenna, concrete steps comprise:

(1) Measure user RFID antenna parameters

Power on, the microcontroller outputs a control signal to make all the magnetic latching relays in an open state, and the series matching capacitors in the series matching capacitor group and the parallel matching capacitors in the parallel matching capacitor group are all in a disconnected state , in an open circuit state at this time, the microcontroller records the voltage value U0 in the open circuit state collected by the analog-to-digital converter ADC, and the microcontroller further controls the magnetic latching relay of the series matching capacitor group, according to the The order of capacitance values of the series matching capacitors from small to large, the series matching capacitors are gradually closed, so that the capacitance value of the access loop is gradually increased, and during the process of gradually increasing the capacitance value, the microcontroller passes the modulus The converter ADC obtains a voltage minimum value, and the voltage minimum value refers to the minimum value of the data obtained by the analog-to-digital converter ADC in continuous sampling of the balun output voltage, which is recorded by the magnetic latching relay The sum Cs0 of the capacitance values of the series matching capacitors of the closed lead access loop, record the minimum voltage value U1, and calculate the value of the inherent series inductance L0 of the antenna metal tube, as shown in the following formula:

L0＝1/(4*pi^2*f0^2*Cs0)

In the formula, pi=3.14, f0 is the center frequency of the RFID antenna, f0=13.56MHz;

Calculate the value of the inherent series resistance R0 as follows:

R0＝Z0*U1/(U0-U1)-Rq

In the formula, Z0 is the impedance of the coaxial feeder, Z0=50 ohms, Rq is the Q value adjustment resistor, and the value range of Rq is 0-4 ohms;

(2) Calculate the capacitance Cp of the parallel matching capacitor that should be connected to the circuit and the capacitance Cs of the series matching capacitor that should be connected to the circuit

In step (1), the inherent series inductance L0 and the inherent series resistance R0 of the antenna metal tube are obtained. According to the calculation formula of the LC matching circuit, the capacitance value Cp of the parallel matching capacitor that should be connected to the circuit and the capacitance value Cp of the series matching capacitor that should be connected to the circuit are obtained. The capacitance value Cs is shown in the following formula:

Cp＝(Z0*Rf-Rf^2)^0.5/(2*pi*f0*Z0*Rf)

Cs＝1/(4*pi^2*f0^2*L0-2*pi*f0*(Z0*Rf-Rf^2)^0.5)

In the formula, Rf=R0+Rq;

(3) Control matching capacitor access

Step (2) obtains the capacitance Cp of the parallel matching capacitor that should be connected to the circuit and the capacitance Cs of the series matching capacitor that should be connected to the circuit, and the microcontroller selects the parallel matching capacitor from the parallel matching capacitor group The combination of the parallel matching capacitors, the combined capacitance value of the parallel matching capacitors is Cp', so that Cp' is closest to Cp, and the combination of the parallel matching capacitors is connected in parallel to the circuit by controlling the magnetic latching relay. Select the combination of series matching capacitors in the series matching capacitor group, the combined capacitance value of the series matching capacitors is Cs', so that Cs' is the closest to Cs, and the combination of the series matching capacitors is connected in series by controlling the magnetic latching relay Into the circuit; wherein, the matching capacitance refers to the combination of the parallel matching capacitance and the combination of the series matching capacitance;

(4) fine-tuning matching points

Fine-tuning the combined capacitance value Cp' of the parallel matching capacitors connected to the circuit and the combined capacitance Cs' of the series matching capacitors connected to the circuit, and the microcontroller fine-tunes the combined capacitance value Cs' of the series matching capacitors connected to the circuit , when |U-U0/2| takes the minimum value, the combined capacitance value Cs” of the corresponding series matching capacitors connected to the circuit is the combined optimal matching capacitance value of the series matched capacitors connected to the circuit, and the microcontroller Fine-tune the combined capacitance value Cp' of the parallel matching capacitors connected to the circuit. When |U-U0/2| The combination of parallel matching capacitors is the best matching capacitor value, and the trimming is completed, wherein, U is the signal amplitude value collected by the microcontroller through the analog-to-digital converter ADC in real time.

After steps (1) to (3), the RFID antenna is basically in a matching state. In order to further weaken measurement and calculation errors, step (4) is performed to fine-tune the matching point.

The operation process of the RFID antenna is as follows: an unbalanced input signal enters the balun through the coaxial feeder, and after being transformed into a balanced signal, flows through the parallel matching capacitor group, the series matching capacitor group and the antenna. The 50 ohm LC resonant impedance transformation network composed of metal pipes is radiated to the outer space by the metal pipe of the antenna, and the Q value adjustment resistor reduces the Q value of the RFID antenna to avoid too narrow bandwidth; when working, the detection circuit samples the The signal at the output terminal of the balun is converted into a voltage amplitude value, and sent to the microcontroller through the analog-to-digital converter ADC, and the microcontroller detects the signal amplitude at the output terminal of the balun, and at the same time, the microcontroller According to the automatic matching method, the controller controls the on-off of each magnetic latching relay through the driving circuit to complete the matching process. The circuit composed of the load modulation triode and the load modulation resistor is mainly used for the microcontroller to generate a load for the signal. The modulated, multiplexed signal is sent to the RFID reader over the coaxial feeder.

The beneficial effects of the present invention are:

The invention provides an automatic matching method for RFID antennas. Users can install RFID readers of different shapes without changing the circuits and RFID readers, which is suitable for different applications and basically makes the RFID antennas optimal. The matching state can also change the matching circuit parameters when the parameters of the RFID reader change to achieve automatic matching, and the simplified matching circuit design ensures bandwidth and economical practicability.

Description of drawings

Fig. 1 is the circuit diagram of RFID antenna of the present invention;

Among them, 1. Coaxial feeder, 2. Balun, 3. Load modulation resistor, 4. Magnetic latching relay, 5. Series matching capacitor, 6. Load modulation transistor, 7. Parallel matching capacitor, 8. Control circuit, 9. Antenna metal tube, 10, inherent series inductance L0, 11, inherent series resistance R0, 12, Q value adjustment resistor, 13, microcontroller, 14, drive circuit, 15, analog-to-digital converter ADC, 16, detection circuit.

detailed description

The present invention is further limited below in conjunction with the accompanying drawings and embodiments, but is not limited thereto.

Example 1

An RFID antenna, comprising a coaxial feeder 1, a balun 2, a load modulation transistor 6, a load modulation resistor 3, a parallel matching capacitor group, a series matching capacitor group, an antenna metal tube 9, a Q value adjusting resistor 12, a control circuit 8, Microcontroller 13, drive circuit 14, detection circuit 16, analog-to-digital converter ADC 15, the parallel matching capacitor group includes seven parallel-connected parallel matching capacitors 7 and magnetic latching relays 4, and the series matching capacitor group includes ten The series matching capacitor 5 and the magnetic latching relay 4 are connected in series, the antenna metal tube 9 includes an inherent series inductance L0 10 and an inherent series resistance R0 11, the coaxial feeder 1 is connected to the input end of the balun 2, and the The output end of the balun 2 is connected to the parallel matching capacitor group, and the output end of the balun 2 is also connected to one end of the series matching capacitor group, and the other end of the series matching capacitor group is connected in series with one end of the antenna metal tube 9, The other end of the antenna metal tube 9 is connected in series with the Q value adjustment resistor 12, and the Q value adjustment resistor 12 is connected to the output end of the balun 2; the output end of the balun 2 is also connected to the input end of the detection circuit 16 , the output terminal of the detection circuit 16 is connected to the analog-to-digital converter ADC 15, the analog-to-digital converter ADC 15 is connected to the microcontroller 13, and one output control signal of the microcontroller 13 is connected to the drive circuit 14, the drive circuit 14 is connected to the control terminals of each magnetic latching relay 4 through the control circuit 8, and the other output control signal of the microcontroller 13 is connected to the base of the load modulation transistor 6, The emitter and collector of the load modulation transistor 6 are connected in parallel with the output terminal of the balun 2 through the load modulation resistor 3 .

The capacitance values of the seven parallel matching capacitors 7 in the parallel matching capacitor group are 2 times from small to large, and the capacitance values of the ten series matching capacitors 5 in the series matching capacitor group are 2 times from small to large.

The capacitance values of the seven parallel matching capacitors 7 in the parallel matching capacitor group are 2 times from small to large, and the capacitance values of the seven parallel matching capacitors 7 in the parallel matching capacitor group are 25p, 50p, 100p, 200p, 400p, 800p, 1600p; the capacitance value of the ten series matching capacitors 5 in the series matching capacitor group becomes 2 times from small to large, and the capacitance value of the ten series matching capacitors 5 in the series matching capacitor group The order is 1p, 2p, 4p, 8p, 16p, 32p, 64p, 128p, 256p, 512p.

The antenna metal tube 9 is bent and replaced by the user. The main parameters of the antenna metal tube 9 are equivalent to the inherent series inductance L0 10 and the inherent series resistance R0 11 .

Example 2

According to the automatic matching method of the RFID antenna described in embodiment 1, the specific steps include:

(1) Measure user RFID antenna parameters

Power on, the microcontroller 13 outputs a control signal to make all the magnetic latching relays 4 in an open circuit state, and the series matching capacitor 5 in the series matching capacitor group and the parallel matching capacitor 7 in the parallel matching capacitor group are both In the disconnected state, it is in an open circuit state at this time, the microcontroller 13 records the voltage value U0 in the open circuit state collected by the analog-to-digital converter ADC 15, and the microcontroller 13 further controls the series matching capacitor group The magnetic latching relay 4, according to the order of the capacitance value of the series matching capacitor 5 from small to large, the series matching capacitor 5 is gradually closed, so that the capacitance value of the access loop is gradually increased, and during the process of gradually increasing the capacitance value, The microcontroller 13 obtains a voltage minimum value through the analog-to-digital converter ADC15, and the voltage minimum value refers to the data obtained by the analog-to-digital converter ADC 15 continuously sampling the output voltage of the balun 2 record the sum Cs0 of the capacitance value of the series matching capacitor 5 connected to the loop by the closed lead of the magnetic latching relay 4, record the minimum value U1 of the voltage, and calculate the intrinsic value of the antenna metal tube 9 The value of the series inductance L0 is shown in the following formula:

L0＝1/(4*pi^2*f0^2*Cs0)

In the formula, pi=3.14, f0 is the center frequency of the RFID antenna, f0=13.56MHz;

Calculate the value of the inherent series resistance R0 as follows:

R0＝Z0*U1/(U0-U1)-Rq

In the formula, Z0 is the impedance of the coaxial feeder 1, Z0=50 ohms, Rq is the Q value adjustment resistor, and the value range of Rq is 0-4 ohms;

(2) Calculate the capacitance Cp of the parallel matching capacitor 7 that should be connected to the circuit and the capacitance Cs of the series matching capacitor 5 that should be connected to the circuit

In step (1), the inherent series inductance L0 and the inherent series resistance R0 of the antenna metal tube are obtained, and according to the calculation formula of the LC matching circuit, the capacitance value Cp of the parallel matching capacitor 7 that should be connected to the circuit and the series matching capacitor that should be connected to the circuit are obtained The capacitance value Cs of 5 is shown in the following formula:

Cp＝(Z0*Rf-Rf^2)^0.5/(2*pi*f0*Z0*Rf)

Cs＝1/(4*pi^2*f0^2*L0-2*pi*f0*(Z0*Rf-Rf^2)^0.5)

In the formula, Rf=R0+Rq;

(3) Control matching capacitor access

Step (2) obtains the capacitance value Cp of the parallel matching capacitor 7 that should be connected to the circuit and the capacitance Cs of the series matching capacitor 5 that should be connected to the circuit, and the microcontroller 13 selects from the parallel matching capacitor group A combination of parallel matching capacitors 7, the combined capacitance value of the parallel matching capacitors 7 is Cp', so that Cp' is closest to Cp, and the combination of the parallel matching capacitors 7 is connected in parallel to the circuit by controlling the magnetic latching relay 4, The microcontroller 13 selects a combination of series matching capacitors 5 from the series matching capacitor group, the combined capacitance value of the series matching capacitors 5 is Cs', so that Cs' is closest to Cs, and by controlling the magnetic latching relay 4. Connecting the combination of the series matching capacitors 5 into the circuit in series; wherein the matching capacitors refer to the combination of the parallel matching capacitors 7 and the combination of the series matching capacitors 5;

(4) fine-tuning matching points

Fine-tuning the combined capacitance Cp' of the parallel matching capacitor 7 of the access circuit and the combined capacitance Cs' of the series matching capacitor 5 of the access circuit, the microcontroller 13 fine-tunes the combination of the series matching capacitor 5 of the access circuit The capacitance value Cs', when |U-U0/2| takes the minimum value, the combined capacitance value Cs" of the series matching capacitor 5 of the corresponding access circuit is the combined best matching capacitance of the series matching capacitor 5 of the access circuit value, the microcontroller 13 fine-tunes the combined capacitance value Cp' of the parallel matching capacitor 7 of the access circuit. When |U-U0/2| takes the minimum value, the combined capacitance of the parallel matching capacitor 7 of the corresponding access circuit The value Cp" is the combined optimal matching capacitance value of the parallel matching capacitance 7 connected to the circuit, and the trimming is completed, wherein U is the signal amplitude value collected by the microcontroller 13 through the analog-to-digital converter ADC 15 in real time.

After steps (1) to (3), the RFID antenna is basically in a matching state. In order to further weaken measurement and calculation errors, step (4) is performed to fine-tune the matching point.

The operation process of the RFID antenna is as follows: an unbalanced input signal enters the balun 2 through the coaxial feeder 1, and after being transformed into a balanced signal, flows through the parallel matching capacitor group, the series matching capacitor group and the The 50 ohm LC resonant impedance conversion network formed by the antenna metal tube 9 is radiated to the outer space by the antenna metal tube 9, and the Q value adjusting resistor 12 reduces the Q value of the RFID antenna so as not to narrow the bandwidth; during work, the The detection circuit 16 samples the output signal of the balun 2, converts it into a voltage amplitude value, and transmits it to the microcontroller 13 through the analog-to-digital converter ADC 15, and the microcontroller 13 detects the barun Lun 2 output terminal signal amplitude, simultaneously described micro-controller 13 controls the on-off of each road described magnetic latching relay 4 by described drive circuit 14 according to automatic matching method, completes the matching process, load modulating triode 6, load modulating resistor The circuit composed of 3 is mainly used for the microcontroller 13 to generate load modulation on the signal, and the multiplexed signal is transmitted to the RFID reader through the coaxial feeder 1.

Claims (3)

1. An RFID antenna, characterized in that it comprises a coaxial feeder, a balun, a load modulation triode, a load modulation resistor, a parallel matching capacitor bank, a series matching capacitor bank, an antenna metal tube, a Q value adjusting resistor, a control circuit, a micro A controller, a drive circuit, a detection circuit, and an analog-to-digital converter ADC, the parallel matching capacitor group includes multiple parallel-connected parallel matching capacitors and magnetic latching relays, and the series matching capacitor group includes multiple series-connected series matching capacitors With a magnetic latching relay, the antenna metal tube includes an inherent series inductance L0 and an inherent series resistance R0, the coaxial feeder is connected to the balun input end, the balun output end is connected to the parallel matching capacitor group, the The output terminal of the balun is also connected to one end of the series matching capacitor group at the same time, the other end of the series matching capacitor group is connected in series with one end of the antenna metal tube, and the other end of the antenna metal tube is connected in series with the Q value adjustment resistor, the The Q value adjustment resistor is connected to the balun output terminal; the balun output terminal is also connected to the input terminal of the detection circuit, and the output terminal of the detection circuit is connected to the analog-to-digital converter ADC, and the analog-to-digital converter The ADC is connected to the microcontroller, and one output control signal of the microcontroller is connected to the drive circuit, and the drive circuit is connected to the control terminals of each magnetic latching relay through the control line, and the microcontroller The other output control signal is connected to the base of the load modulation transistor, and the emitter and collector of the load modulation transistor are connected in parallel with the output terminal of the balun through the load modulation resistor. 2. according to the described RFID antenna of claim 1, it is characterized in that, the capacitance value of a plurality of parallel matching capacitors in the parallel matching capacitor group is from small to large into a 2-fold relationship, and a plurality of series matching capacitors in the series matching capacitor group The capacitance value of the matching capacitor is doubled from small to large. 3. according to the automatic matching method of RFID antenna described in claim 1 or 2, it is characterized in that, concrete steps comprise: (1) Measure user RFID antenna parameters Power on, the microcontroller outputs a control signal to make all the magnetic latching relays in an open state, and the series matching capacitors in the series matching capacitor group and the parallel matching capacitors in the parallel matching capacitor group are all in a disconnected state , in an open circuit state at this time, the microcontroller records the voltage value U0 in the open circuit state collected by the analog-to-digital converter ADC, and the microcontroller further controls the magnetic latching relay of the series matching capacitor group, according to the The order of capacitance values of the series matching capacitors from small to large, the series matching capacitors are gradually closed, so that the capacitance value of the access loop is gradually increased, and during the process of gradually increasing the capacitance value, the microcontroller passes the modulus The converter ADC obtains a voltage minimum value, and the voltage minimum value refers to the minimum value of the data obtained by the analog-to-digital converter ADC in continuous sampling of the balun output voltage, which is recorded by the magnetic latching relay The sum Cs0 of the capacitance values of the series matching capacitors of the closed lead access loop, record the minimum voltage value U1, and calculate the value of the inherent series inductance L0 of the antenna metal tube, as shown in the following formula: L0＝1/(4*pi^2*f0^2*Cs0) In the formula, pi=3.14, f0 is the center frequency of the RFID antenna, f0=13.56MHz; Calculate the value of the inherent series resistance R0 as follows: R0＝Z0*U1/(U0-U1)-Rq In the formula, Z0 is the impedance of the coaxial feeder, Z0=50 ohms, Rq is the Q value adjustment resistor, and the value range of Rq is 0-4 ohms; (2) Calculate the capacitance Cp of the parallel matching capacitor that should be connected to the circuit and the capacitance Cs of the series matching capacitor that should be connected to the circuit In step (1), the inherent series inductance L0 and the inherent series resistance R0 of the antenna metal tube are obtained. According to the calculation formula of the LC matching circuit, the capacitance value Cp of the parallel matching capacitor that should be connected to the circuit and the capacitance value Cp of the series matching capacitor that should be connected to the circuit are obtained. The capacitance value Cs is shown in the following formula: Cp＝(Z0*Rf-Rf^2)^0.5/(2*pi*f0*Z0*Rf) Cs＝1/(4*pi^2*f0^2*L0-2*pi*f0*(Z0*Rf-Rf^2)^0.5) In the formula, Rf=R0+Rq; (3) Control matching capacitor access Step (2) obtains the capacitance Cp of the parallel matching capacitor that should be connected to the circuit and the capacitance Cs of the series matching capacitor that should be connected to the circuit, and the microcontroller selects the parallel matching capacitor from the parallel matching capacitor group The combination of the parallel matching capacitors, the combined capacitance value of the parallel matching capacitors is Cp', so that Cp' is closest to Cp, and the combination of the parallel matching capacitors is connected in parallel to the circuit by controlling the magnetic latching relay. Select the combination of series matching capacitors in the series matching capacitor group, the combined capacitance value of the series matching capacitors is Cs', so that Cs' is the closest to Cs, and the combination of the series matching capacitors is connected in series by controlling the magnetic latching relay Into the circuit; wherein, the matching capacitance refers to the combination of the parallel matching capacitance and the combination of the series matching capacitance; (4) fine-tuning matching points Fine-tuning the combined capacitance value Cp' of the parallel matching capacitors connected to the circuit and the combined capacitance Cs' of the series matching capacitors connected to the circuit, and the microcontroller fine-tunes the combined capacitance value Cs' of the series matching capacitors connected to the circuit , when |U-U0/2| takes the minimum value, the combined capacitance value Cs” of the corresponding series matching capacitors connected to the circuit is the combined optimal matching capacitance value of the series matched capacitors connected to the circuit, and the microcontroller Fine-tune the combined capacitance value Cp' of the parallel matching capacitors connected to the circuit. When |U-U0/2| The combination of parallel matching capacitors is the best matching capacitor value, and the trimming is completed, wherein, U is the signal amplitude value collected by the microcontroller through the analog-to-digital converter ADC in real time.