Anti-howling wireless sound box based on impedance matching

Abstract

The utility model discloses anti-howling wireless sound equipment based on impedance matching. The anti-howling wireless sound equipment comprises a howling suppression circuit arranged between a wireless receiver and a power amplifier board, the howling suppression circuit comprises an impedance detection module, a microcontroller and a programmable impedance adjustment module which are connected in sequence; the impedance detection module is connected with an audio input line, detects an impedance value of an input audio signal in real time, and transmits detection data to the microcontroller; the microcontroller analyzes and processes the received impedance data, and calculates an impedance adjustment parameter according to a preset matching rule; the programmable impedance adjusting module dynamically adjusts the impedance value of the programmable impedance adjusting module according to the impedance adjusting parameters output by the microcontroller; according to the utility model, the dynamic accurate matching of the output signal impedance of the wireless receiver and the input impedance of the power amplifier board can be realized, a positive feedback loop formed by signal reflection is eliminated, the howling problem caused by impedance mismatching is solved, and the defect of signal distortion caused by the fact that a fixed parameter RC filter circuit cannot dynamically cope with interference is avoided.

Description

A wireless speaker with anti-feedback based on impedance matching Technical Field

[0001] This utility model relates to the field of intelligent speaker technology, and more specifically to an anti-feedback wireless speaker based on impedance matching. Background Technology

[0002] Currently, the connection design between wireless receivers and power amplifier boards often employs a simple direct connection or only a fixed-parameter RC filter circuit. With this connection method, on the one hand, the impedance of the wireless receiver's output signal is difficult to precisely match with the input impedance of the power amplifier board, easily causing signal reflection, forming a positive feedback loop, and thus triggering howling. On the other hand, the teaching environment contains various wireless signal interferences (such as WiFi and Bluetooth device signals). Existing fixed-parameter RC filter circuits can only filter preset frequency bands to a limited extent and cannot dynamically cope with signal distortion caused by interference. After the distorted signal is amplified by the power amplifier board, it significantly increases the possibility of howling.

[0003] Meanwhile, existing technologies often lack effective shielding and anti-interference designs for the connection cables between wireless receivers and amplifier boards. In the complex electromagnetic environment of classrooms, these cables are prone to coupling with external interference signals. These interference signals are amplified after entering the amplifier board, interfering with the transmission of normal audio signals. The interaction between the interference signals and the audio signals can also easily trigger feedback. Furthermore, most teaching audio systems do not have dedicated signal buffering and limiting devices designed for the connection between the wireless receiver and the amplifier board. When the signal strength of the wireless microphone changes abruptly, the amplifier board may receive an excessively large signal instantaneously, potentially leading to overload distortion and ultimately causing feedback problems.

[0004] Therefore, how to achieve howling suppression is a problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0005] In view of this, the present invention provides a wireless speaker with anti-feedback based on impedance matching, which can achieve dynamic and precise matching between the output signal impedance of the wireless receiver and the input impedance of the power amplifier board, eliminate the positive feedback loop formed by signal reflection, solve the feedback problem caused by impedance mismatch, and avoid the defect of fixed parameter RC filter circuits being unable to dynamically cope with interference and cause signal distortion.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] An anti-feedback wireless speaker based on impedance matching includes a wireless receiver and an amplifier board, as well as a feedback suppression circuit disposed between the wireless receiver and the amplifier board.

[0008] The feedback suppression circuit includes an impedance detection module, a microcontroller, and a programmable impedance adjustment module connected in sequence. The impedance detection module is connected to the audio input line, detects the impedance value of the input audio signal in real time, and transmits the detected data to the microcontroller. The microcontroller analyzes and processes the received impedance data and calculates the impedance adjustment parameters according to preset matching rules. The programmable impedance adjustment module dynamically adjusts its own impedance value according to the impedance adjustment parameters output by the microcontroller.

[0009] Preferably, the programmable impedance adjustment module includes a digitally controlled resistor array, a programmable capacitor array, and an impedance switching control circuit;

[0010] The input terminal of the impedance switching control circuit is connected to the microcontroller, and the two output terminals are respectively connected to the numerically controlled resistor array and the programmable capacitor array.

[0011] Preferably, the numerically controlled resistor array includes multiple parallel resistors, with the weights of each resistor distributed according to a specific weighting, and each resistor is connected in series with a MOSFET switch.

[0012] Preferably, the programmable capacitor array includes multiple groups of surface-mount capacitors with different capacitance values, and each group of capacitors is provided with an analog switch connection circuit.

[0013] Preferably, the impedance switching control circuit includes a decoder and a driver chip; the decoder is connected to the microcontroller, receives the control signal output by the microcontroller and decodes it into a multiplexer control signal;

[0014] The driver chip is connected to the decoder and amplifies the output signal of the decoder to drive the corresponding switch control pins in the numerically controlled resistor array or the programmable capacitor array.

[0015] Preferably, the impedance detection module includes a high-frequency detection circuit and a multi-band sampling circuit;

[0016] The high-frequency detection circuit and the multi-frequency sampling circuit are respectively connected to the output of the wireless receiver to receive audio signals.

[0017] Preferably, in the high-frequency detection circuit, a timer generates a square wave of a specific high frequency, which is then converted into a constant current signal by an operational amplifier and a precision resistor and injected into the audio circuit.

[0018] An isolation transformer has its primary winding connected in series between a constant current source and an audio circuit, and its secondary winding connected in parallel across a sampling resistor.

[0019] Two instrumentation amplifiers are used to amplify the voltage of the audio line and the sampling resistor respectively before inputting them to the phase detection chip;

[0020] The two amplified signals are multiplied by an analog multiplier in the detection chip to generate a mixed signal containing phase difference information; after passing through a low-pass filter, the output impedance magnitude and the DC voltage corresponding to the phase difference are sent to the microcontroller.

[0021] Preferably, the multi-band sampling circuit includes a filter bank, an analog switch array, and a sample-and-hold unit;

[0022] The filter bank uses multiple sets of filters with different frequency bands to divide the audio signal;

[0023] The analog switch array is connected to the filter bank and is used to control the output of the filter bank;

[0024] The sample-and-hold unit consists of a sampling switch, a holding capacitor, and a buffer amplifier. The sampling switch receives a sampling control signal from the microcontroller and turns on at a specified time to sample the specific frequency band audio signal output by the analog switch array, storing the signal voltage in the holding capacitor. The buffer amplifier is an operational amplifier with high input impedance and low output impedance, which isolates and amplifies the voltage on the holding capacitor before outputting it to the ADC unit of the microcontroller.

[0025] Preferably, the microcontroller acquires the outputs of the high-frequency detection circuit and the multi-band sampling circuit through the ADC unit;

[0026] Used to calculate impedance based on the converted voltage and current digital quantities output by the high-frequency detection circuit through a built-in multiplier;

[0027] The circuit is used to drive the built-in timer to generate a PWM waveform based on the output of the multi-band sampling circuit, forming an adjustable current superimposed on the constant current source in the high-frequency detection circuit.

[0028] As can be seen from the above technical solution, compared with the prior art, this utility model discloses a wireless speaker with anti-feedback based on impedance matching. It achieves dynamic and precise matching between the output signal impedance of the wireless receiver and the input impedance of the power amplifier board through the feedback suppression circuit, eliminates the positive feedback loop formed by signal reflection, solves the feedback problem caused by impedance mismatch, and avoids the defect of fixed parameter RC filter circuits that cannot dynamically cope with interference and cause signal distortion.

[0029] This invention proposes a high-frequency detection circuit and a multi-band complementary detection network, which helps to achieve high-precision impedance measurement. At the same time, by sampling and maintaining the synchronous data of the unit, it avoids signal lag caused by time-division sampling and ensures the timeliness and integrity of the detection data.

[0030] The numerically controlled resistor array (with discrete adjustable resistance value) and the programmable capacitor array (with continuous / discrete adjustable capacitive reactance) are integrated into the same hardware link through a parallel topology, which can simultaneously adjust the resistive component and the reactance component (capacitive reactance) to achieve full parameter matching of complex impedance. Attached Figure Description

[0031] To more clearly illustrate the technical solutions in the embodiments of this utility model or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of this utility model. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0032] Figure 1 is a schematic diagram of an anti-feedback wireless speaker structure based on impedance matching provided by this utility model.

[0033] Figure 2 is a schematic diagram of the impedance detection module in an embodiment of this utility model.

[0034] Figure 3 is a schematic diagram of the programmable impedance adjustment module in an embodiment of this utility model. Detailed Implementation

[0035] The technical solutions of the present utility model will be clearly and completely described below with reference to the accompanying drawings of the embodiments. Obviously, the described embodiments are only some embodiments of the present utility model, and not all embodiments. Based on the embodiments of the present utility model, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the protection scope of the present utility model.

[0036] As shown in Figure 1, this utility model embodiment discloses an anti-feedback wireless speaker based on impedance matching, including a wireless receiver and a power amplifier board, as well as a feedback suppression circuit disposed between the wireless receiver and the power amplifier board.

[0037] The feedback suppression circuit includes an impedance detection module, a microcontroller, and a programmable impedance adjustment module connected in sequence. The impedance detection module is connected to the audio input line, detects the impedance value of the input audio signal in real time, and transmits the detection data to the microcontroller. The microcontroller analyzes and processes the received impedance data and calculates the impedance adjustment parameters according to the preset matching rules. The programmable impedance adjustment module dynamically adjusts its own impedance value according to the impedance adjustment parameters output by the microcontroller.

[0038] Feedback (howling) requires two conditions: phase and gain. For the phase condition, the audio signal output from the speaker, after being reflected back to the microphone, must have a phase shift of 0° or an integer multiple of 360° (i.e., positive feedback). For the gain condition, the gain of the feedback signal must be greater than the total system attenuation, causing the signal to be continuously amplified until distortion occurs. Traditional anti-feedback technologies (such as notch filtering) eliminate feedback by attenuating specific frequencies, but this may damage sound quality. This embodiment, however, uses dynamic impedance matching to disrupt the feedback condition at the circuit level.

[0039] As shown in Figure 2, in order to further implement the above technical solution, the impedance detection module includes a high-frequency detection circuit and a multi-band sampling circuit; the high-frequency detection circuit and the multi-band sampling circuit are respectively connected to the output of the wireless receiver to receive audio signals.

[0040] This embodiment sets up two detection circuits. The high-frequency detection circuit is based on the constant current source injection method and calculates the impedance by detecting the voltage / current phase difference. The multi-band sampling circuit divides the signal into low, medium, and high frequency bands, such as 20Hz to 20kHz, and analyzes the impedance characteristics of each band to locate the howling sensitive frequency band.

[0041] Furthermore, the advantages of high-frequency detection circuits are: high-frequency signals can isolate low-frequency components in audio (such as human voices), avoiding detection interference, and are suitable for accurate measurement of impedance magnitude and phase in real time. In the high-frequency detection circuit, a timer generates a square wave of a specific high frequency, which is then used by an operational amplifier and a precision resistor to generate a constant current signal that is injected into the audio circuit; there is an isolation transformer, whose primary winding is connected in series between the constant current source and the audio circuit, and whose secondary winding is connected in parallel across a sampling resistor; two instrumentation amplifiers amplify the voltages of the audio circuit and the sampling resistor respectively, and then input them to the phase detection chip; the two amplified signals are multiplied by an analog multiplier in the detection chip to generate a mixed signal containing phase difference information; after passing through a low-pass filter, the DC voltage corresponding to the impedance magnitude and phase difference is output to the microcontroller.

[0042] Specifically, a timer generates a high-frequency square wave, which is converted into a constant current signal by an operational amplifier and a precision resistor. This signal is then injected into the audio circuit through an isolation transformer. The primary winding of the isolation transformer is connected in series between the constant current source and the audio circuit, while the secondary winding is connected in parallel with a sampling resistor. The two signals, the audio circuit voltage and the sampling resistor voltage, are collected and amplified by an instrumentation amplifier before being input to a phase detection chip. The phase difference is calculated by an analog multiplier, and a low-pass filter outputs a DC voltage corresponding to the impedance magnitude and phase difference.

[0043] For example, in the high-frequency detection circuit, a NE555 timer chip is used to generate a 20kHz square wave signal, which is then used by a high-precision operational amplifier AD8628 and a precision resistor network (1% accuracy) to generate a 1mA constant current signal injected into the audio circuit. An EPCOS B78471S series isolation transformer is used, with its primary winding connected in series between the constant current source and the audio circuit, and its secondary winding connected in parallel with a 10Ω sampling resistor. Two INA128 instrumentation amplifiers are used to amplify the voltages on the audio circuit and the sampling resistor, respectively, and output to the phase detection chip AD630. The analog multiplier within the AD630 multiplies the two amplified signals, and after passing through a low-pass filter (cutoff frequency 100Hz), outputs a DC voltage corresponding to the impedance magnitude and phase difference to the microcontroller.

[0044] The advantage of a multi-band sampling circuit lies in its ability to combine frequency domain analysis with targeted impedance adjustment of the feedback-sensitive frequency bands, thereby improving suppression accuracy. A multi-band sampling circuit includes a filter bank, an analog switch array, and a sample-and-hold unit. The filter bank uses multiple filters of different frequency bands to divide the audio signal. The analog switch array is connected to the filter bank and is used to control its output. The sample-and-hold unit consists of a sampling switch, a holding capacitor, and a buffer amplifier. The sampling switch receives the sampling control signal from the microcontroller, turns on at a specified time, samples the specific frequency band audio signal output by the analog switch array, and stores the signal voltage in the holding capacitor. The buffer amplifier uses a high input impedance, low output impedance operational amplifier to isolate and amplify the voltage on the holding capacitor before outputting it to the microcontroller's ADC unit.

[0045] Specifically, the filter bank employs multiple bandpass filters (such as Butterworth filters), for example: low-frequency band (20Hz~500Hz), mid-frequency band (500Hz~3kHz), and high-frequency band (3kHz~20kHz). An analog switch array, controlled by a microcontroller, time-divisionally selects the outputs of each frequency band filter to avoid signal aliasing. A sampling switch (such as CD4051) is triggered by the microcontroller's PWM signal to sample the target frequency band signal and store it in a holding capacitor (such as 10nF). A buffer amplifier (such as OPA27) isolates the holding capacitor voltage and outputs it to the MCU's ADC unit to digitize the amplitude of each frequency band signal.

[0046] To further implement the above technical solution, the microcontroller obtains the outputs of the high-frequency detection circuit and the multi-band sampling circuit through the ADC unit; it is used to calculate the impedance through a built-in multiplier based on the converted voltage and current digital quantities output by the high-frequency detection circuit; and it is used to drive the built-in timer to generate a PWM waveform based on the output of the multi-band sampling circuit, forming an adjustable current superimposed on the constant current source in the high-frequency detection circuit.

[0047] Specifically, the microcontroller receives the analog voltage output from the high-frequency detection circuit through a 12-bit ADC channel and converts it into a digital quantity; at the same time, it uses an analog multiplexer to sample the multi-band sampling circuit signal in a time-division manner using a 24-channel ADC array. The microcontroller has a built-in hardware multiplier that outputs converted digital voltage and current values ​​from the high-frequency detection circuit (the voltage value comes from the amplified value of the audio line voltage after being amplified by an instrumentation amplifier, and the current value comes from the amplified value of the voltage across the sampling resistor after being amplified by an instrumentation amplifier). The microcontroller's GPIO pins output 3-bit binary levels to control the analog switch array for frequency band selection; a timer generates a PWM waveform, which is converted into an analog voltage by an RC low-pass filter to adjust the constant current source; a timer update event generates a synchronization pulse signal to trigger the sample-and-hold chip. When the ADC value of a certain frequency band in the multi-band sampling circuit exceeds the 2V threshold set by the hardware potentiometer, the analog switch keeps that channel conducting. The hardware gain coefficient is a fixed coefficient pre-determined based on the characteristics of each frequency band through experimental or theoretical calculations and stored in the hardware, used to specifically adjust the signal strength of the corresponding frequency band. At this time, the microcontroller uses the hardware analog multiplier to multiply the 10kHz impedance value of the high-frequency detection circuit by the corresponding hardware gain coefficient, ultimately outputting a binary control signal to drive the external circuit to adjust the impedance.

[0048] When analyzing multi-band signals, the microcontroller uses existing frequency domain energy calculation algorithms, such as fast Fourier transform or direct spectrum analysis, to calculate the energy distribution of each frequency band. Then, it identifies energy anomalies through threshold comparison or dynamic averaging algorithms. Finally, it uses control logic algorithms, such as PID control algorithms, to adjust the constant current source.

[0049] As shown in Figure 3, in order to further implement the above technical solution, the programmable impedance adjustment module includes a digitally controlled resistor array, a programmable capacitor array, and an impedance switching control circuit; the input terminal of the impedance switching control circuit is connected to the microcontroller, and the two output terminals are connected to the digitally controlled resistor array and the programmable capacitor array, respectively.

[0050] Specifically, the numerically controlled resistor array includes multiple parallel resistors, with each resistor having a specific weight distribution, and each resistor is connected in series with a MOSFET switch; the programmable capacitor array includes multiple sets of surface-mount capacitors with different capacitance values, and each set of capacitors is equipped with an analog switch access circuit; the impedance switching control circuit includes a decoder and a driver chip; the decoder is connected to the microcontroller, receives the control signal output by the microcontroller, and decodes it into multiple switch control signals; the driver chip is connected to the decoder, amplifies the output signal of the decoder, and is used to drive the corresponding switch control pins in the numerically controlled resistor array or programmable capacitor array.

[0051] For example, in a numerically controlled resistor array, there is a multi-parallel resistor network, with the weight of each resistor distributed in binary or decimal (e.g., 1Ω, 2Ω, 4Ω, 8Ω, etc.) to facilitate the combination of precise resistance values; each resistor is connected in series with a MOSFET switch (e.g., IRF530), and the on / off state is controlled by a microcontroller through a decoder (e.g., 74HC138) and a driver chip (e.g., ULN2003). The resistance can be continuously adjusted from 0 to 65535Ω (in 1Ω steps) through 16 resistors to meet different load impedance requirements.

[0052] In a programmable capacitor array, multiple groups of surface-mount capacitors with different capacitance values ​​(e.g., 1nF, 10nF, 100nF, etc.) are connected in parallel to the circuit via an analog switch (e.g., MAX3136). The microcontroller selects the corresponding capacitor combination based on the capacitive reactance calculation, adjusting the capacitive component of the AC impedance. For high-frequency whistling (e.g., >3kHz), the capacitive reactance is reduced by adding capacitors, altering the phase characteristics and disrupting the positive feedback condition.

[0053] In the impedance switching control circuit, the decoder receives the digital signal from the MCU (such as 8-bit binary code), decodes it into multiplexer control signals (such as 16 channels), corresponding to each branch of the resistor / capacitor array, and the driver chip amplifies the decoder output signal (such as current amplification to 50mA) to ensure reliable conduction of MOSFETs or analog switches and reduce signal attenuation.

[0054] In this embodiment, the power amplifier board can use the TPA3116D2 as the main chip. The VDD pin (12V power input) of the TPA3116D2 is connected to a 12V regulated power supply, and a 100μF electrolytic capacitor (C1) and a 0.1μF ceramic capacitor (C2) are connected in parallel to ground for power filtering. The AGND (analog ground) and PGND (power ground) pins are connected to the system ground plane respectively, and grounded at a single point on the PCB to avoid ground loop interference.

[0055] The positive terminal (L+) of the left channel output of the programmable impedance adjustment module is connected to the INL+ pin (pin 12) of the TPA3116D2, and the negative terminal (L-) is connected to the INL- pin (pin 11). The positive terminal (R+) of the right channel output is connected to the INR+ pin (pin 10), and the negative terminal (R-) is connected to the INR- pin (pin 9).

[0056] An RC network consisting of 10Ω resistors (R1, R2, R3, R4) and 0.1μF capacitors (C3, C4, C5, C6) connected in series on each audio input signal line is used for high-frequency filtering to suppress possible high-frequency howling.

[0057] The SD (shutdown control) pin (pin 13) of the TPA3116D2 is connected to VDD through a 10kΩ pull-up resistor and to ground through a 0.1μF capacitor to ensure that the power amplifier starts normally when the system is powered on.

[0058] The MODE pin (pin 14) is connected to ground and set to fixed 26dB gain mode. A 10μF ceramic capacitor (C7) is connected between the BOOT pin (pin 1) and the SW1 pin (pin 2) for bootstrapping.

[0059] The SW1 (pin 2) and SW2 (pin 8) pins of the TPA3116D2 are connected to the LC output filter network, and the output of the filter network is connected to a 4Ω speaker load.

[0060] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For the apparatus disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the description is relatively simple; relevant parts can be referred to the method section.

[0061] The above description of the disclosed embodiments enables those skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A wireless speaker with anti-feedback based on impedance matching, characterized in that, The device includes a wireless receiver and a power amplifier board, as well as a feedback suppression circuit disposed between the wireless receiver and the power amplifier board; the feedback suppression circuit includes an impedance detection module, a microcontroller, and a programmable impedance adjustment module connected in sequence; the impedance detection module is connected to the audio input line, detects the impedance value of the input audio signal in real time, and transmits the detection data to the microcontroller. The microcontroller analyzes and processes the received impedance data and calculates the impedance adjustment parameters according to the preset matching rules; the programmable impedance adjustment module dynamically adjusts its own impedance value according to the impedance adjustment parameters output by the microcontroller.

2. The anti-feedback wireless speaker based on impedance matching according to claim 1, characterized in that, The programmable impedance adjustment module includes a digitally controlled resistor array, a programmable capacitor array, and an impedance switching control circuit; the input terminal of the impedance switching control circuit is connected to the microcontroller, and the two output terminals are respectively connected to the digitally controlled resistor array and the programmable capacitor array.

3. A wireless speaker with anti-feedback based on impedance matching according to claim 2, characterized in that, The numerically controlled resistor array includes multiple parallel resistors, with each resistor having a specific weight distribution, and each resistor is connected in series with a MOSFET switch.

4. A wireless speaker with anti-feedback based on impedance matching according to claim 2, characterized in that, The programmable capacitor array includes multiple groups of surface-mount capacitors with different capacitance values, and each group of capacitors is equipped with an analog switch connection circuit.

5. A wireless speaker with anti-feedback based on impedance matching according to claim 2, characterized in that, The impedance switching control circuit includes a decoder and a driver chip; the decoder is connected to the microcontroller, receives the control signal output by the microcontroller and decodes it into a multiplexer control signal; the driver chip is connected to the decoder, amplifies the output signal of the decoder, and drives the corresponding switch control pins in the numerically controlled resistor array or the programmable capacitor array.

6. A wireless speaker with anti-feedback based on impedance matching according to claim 1, characterized in that, The impedance detection module includes a high-frequency detection circuit and a multi-band sampling circuit; the high-frequency detection circuit and the multi-band sampling circuit are respectively connected to the output terminal of the wireless receiver to receive audio signals.

7. A wireless speaker with anti-feedback based on impedance matching according to claim 6, characterized in that, In the high-frequency detection circuit, a timer generates a square wave of a specific high frequency, which is then used by an operational amplifier and a precision resistor to generate a constant current signal that is injected into the audio line. An isolation transformer has its primary winding connected in series between the constant current source and the audio line, and its secondary winding connected in parallel across a sampling resistor. Two instrumentation amplifiers amplify the voltages of the audio line and the sampling resistor, respectively, and then input them to the phase detection chip. The two amplified signals are multiplied by an analog multiplier within the detection chip to generate a mixed signal containing phase difference information. After passing through a low-pass filter, the output impedance magnitude and the DC voltage corresponding to the phase difference are sent to the microcontroller.

8. A wireless speaker with anti-feedback based on impedance matching according to claim 7, characterized in that, The multi-band sampling circuit includes a filter bank, an analog switch array, and a sample-and-hold unit. The filter bank uses multiple sets of filters with different frequency bands to divide the audio signal. The analog switch array is connected to the filter bank and is used to control the output of the filter bank. The sample-and-hold unit consists of a sampling switch, a holding capacitor, and a buffer amplifier. The sampling switch receives a sampling control signal from the microcontroller, turns on at a specified time, samples the specific frequency band audio signal output by the analog switch array, and stores the signal voltage in the holding capacitor. The buffer amplifier is an operational amplifier with high input impedance and low output impedance, which isolates and amplifies the voltage on the holding capacitor before outputting it to the ADC unit of the microcontroller.

9. A wireless speaker with anti-feedback based on impedance matching according to claim 8, characterized in that, The microcontroller acquires the outputs of the high-frequency detection circuit and the multi-band sampling circuit through the ADC unit; it is used to calculate the impedance through a built-in multiplier based on the converted voltage and current digital values ​​output by the high-frequency detection circuit; and it is used to drive a built-in timer to generate a PWM waveform based on the output of the multi-band sampling circuit, forming an adjustable current superimposed on the constant current source in the high-frequency detection circuit.

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