Measurement device and test method of audio amplifier module

Abstract

The invention aims to provide a measuring device and a testing method for an audio amplifier module. The system comprises a main control board, a DMM test board, a frequency processing board, a test signal adapter board and a to-be-tested audio module, the to-be-tested audio module is connected to the frequency processing board through the test signal adapter board, the frequency processing board is connected to the main control board through the DMM test board, the frequency processing board is connected with the main control board, and the to-be-tested audio module is connected with the main control board through the DMM test board. The frequency processing board comprises a converter, a comparator, an instrumentation amplifier and an operational amplifier, the input end of the instrumentation amplifier is connected with an audio module to be tested, the IN1 end of the converter is connected with the output end of the instrumentation amplifier and the reverse input end of the comparator, the VOUT end of the converter is connected with the DMM test board, and the operational amplifier is connected with the DMM test board. And the non-inverting input end of the comparator is connected with the operational amplifier. The method is applied to the technical field of alternating signal measurement.

Description

Technical Field

[0001] The present invention is applied to the technical field of alternating signal measurement, and in particular relates to a measuring device and a testing method for an audio amplifier module. Background Art

[0002] At present, the common test method for testing frequency and RMS value is to use an oscilloscope for measurement. The oscilloscope measures the frequency of the audio signal by measuring the inverse of its period T. The period T is equal to the scanning period rate T=t / div of the oscilloscope on the X-axis, so f=1 / T is calculated. This is how to measure frequency using an oscilloscope. The oscilloscope measures the RMS value of the audio signal, which is a continuous AC signal. This is because the alternating signal of the audio signal changes with time. Assuming that the continuous signal is S(t), in the time interval [t1, t2], the formula for calculating the RMS value is, Its essence is to square S(t), integrate it over a specific time interval, and then divide it by the length of the time interval to calculate the RMS value. Based on the current solution to replace the oscilloscope, on the one hand, the instrument is expensive to purchase and the procurement cycle is as long as 2 months or even longer. On the other hand, the oscilloscope is large in size, and the space for fixture testing is limited, which is not conducive to small fixture integration and automated testing. Considering that if a solution is integrated on the board, it is very convenient to test multiple channels simultaneously and upload the data to the PC. At the same time, integration also helps to quickly build the entire test solution.

[0003] However, the existing technology has the disadvantages of testing the frequency and root mean square value of the audio amplifier module: since the signal output by the audio amplifier is an AC signal with a certain working periodicity, the measurement and analysis of this signal usually requires the use of instruments and meters for measurement, and the conventional measuring instrument is an oscilloscope. On the one hand, the frequency and root mean square value measured by ordinary Tektronix oscilloscopes such as TBS2000B are not accurate and have certain errors. The reason for the error is that the oscilloscope does not have a high-precision time reference circuit, so there is an error in the frequency measurement. On the one hand, if a high-precision Tektronix oscilloscope such as MSO44 oscilloscope is used, it is expensive and has a high procurement cost. If multiple channels need to be tested simultaneously, using multiple oscilloscopes will make the machine equipment redundant and the installation space limited. Therefore, it is necessary to provide a measurement device and test method for an audio amplifier module, which has the advantages of small board size, easy installation, suitable for measuring the frequency value and root mean square of the audio amplifier, realizing parallel replacement of instruments and meters, and reducing costs and increasing efficiency. Summary of the invention

[0004] The technical problem to be solved by the present invention is to overcome the deficiencies of the prior art and provide a measuring device and a testing method for an audio amplifier module, which has the advantages of small board size and convenient installation, and is suitable for measuring the frequency value and root mean square of an audio amplifier, realizing parallel replacement of instruments and meters, and reducing costs and increasing efficiency.

[0005] The technical solution adopted by the present invention is: the present invention includes a main control board, a DMM test board, a frequency processing board, a test signal adapter board, and an audio module to be tested. The audio module to be tested is connected to the frequency processing board via the test signal adapter board, the frequency processing board is connected to the main control board via the DMM test board, the frequency processing board is connected to the main control board, the frequency processing board includes a converter, a comparator, an instrument amplifier and an operational amplifier, the input end of the instrument amplifier is connected to the audio module to be tested, the IN1 end of the converter is connected to the output end of the instrument amplifier and the reverse input end of the comparator, the VOUT end of the converter is connected to the DMM test board, and the same-direction input end of the comparator is connected to the operational amplifier.

[0006] It can be seen from the above scheme that this application is suitable for testing the RMS value and frequency value of the audio signal of the audio module to be tested. The board is small in size and easy to install. It can replace the desktop multimeter 34465A. In specific function testing, it can realize the parallel replacement of instruments and meters, which has the effect of reducing costs and increasing efficiency. It can improve the test accuracy of the measurement signal, and integrate the hardware circuit solution to realize the feasibility of multi-channel testing at the same time; on the one hand, the integrated hardware circuit also has significant advantages in debugging and installation, which realizes the miniaturization of test equipment and the feasibility of automated testing. In addition, the board is a customized board with the characteristics of being small and precise, and is specially used for measurements of specific frequencies and amplitudes.

[0007] A preferred solution is that the frequency processing board also includes a mechanical relay and an optocoupler switch, the pin3 and pin6 of the mechanical relay are respectively connected to the TP8_SPKR_R_OUT_M and TP7_SPKR_R_OUT_P pins of the audio module to be tested, the RMS_To_DC pin of the optocoupler switch is connected to the VOUT end of the converter, and the DMM_Volt_P pin of the optocoupler switch is connected to the corresponding pin of the DMM test board.

[0008] A preferred solution is that the frequency processing board also includes a low-pass filter circuit and a high-pass filter circuit, and the pin4 pin and the pin5 pin of the mechanical relay are connected to the input end of the instrument amplifier via the low-pass filter circuit and the high-pass filter circuit in sequence, the low-pass filter circuit includes a first inductor, a second inductor, a first capacitor, and a second capacitor, and the high-pass filter circuit includes a first resistor, a second resistor, a third capacitor, and a fourth capacitor.

[0009] A preferred solution is that the main control board includes a main control MCU.

[0010] A preferred solution is that the audio module to be tested includes an audio amplifier.

[0011] A preferred solution is a method for testing a measuring device of an audio amplifier module, the method comprising the following steps: Step 1, the mechanical relay sets the level state of pin8 OUTPUT_BIT14 to low level 0, and the mechanical relay is normally open and closed, at this time, pin6 and pin5, pin3 and pin4 are connected; Step 2, the optocoupler switch sets the pin8 pin OUTPUT_BIT14 level state to a low level, the optocoupler power supply voltage forms a loop through the light-emitting diode and GND, and current flows through the light-emitting diode, thereby driving the light-emitting diode to light up, and the light is detected, so that the mechanical relay is turned on between the normally open pins pin4 and pin3, and the signal will convert Vrms into a DC voltage value after passing through the converter, and then the DC voltage value will be directly given to the ADC analog-to-digital conversion chip for collection; Step 3: Through I2S communication, the main control MCU as the host will send instructions to the audio amplifier to configure and initialize the audio amplifier, where the key register 1: 0x2090, Setting register write parameters refers to the speaker channel volume control, setting Speaker Channel Volume The value written to Control register address: 0x2090 is 0x00 (0dB) to ensure that the signal is 0dB; for key register 2: 0x2092, setting the register write parameter refers to the audio amplifier output configuration, setting the Speaker AmplifierOutput Configuration register address: 0x2092 to write 0x03, SPK_AMP_MODE=0 sets the working mode to: Single-cell mode (default for MAX98388), and SPK_GAIN[2:0]=3, that is, at this time MAX98388 is set to Single-cell Mode: 2.11VRMS (+6dB); Step 4: After the basic operation settings of the audio amplifier are initialized in step 3, the Vp-p voltage of the AC signal of the audio amplifier is calculated by the formula: At this time, the Vp-p peak-to-peak voltage output by the output pins SPKR_R_OUT_P and SPKR_R_OUT_N of the audio signal will first pass through the low-pass filter circuit with a cut-off frequency of f1 and the high-pass filter circuit with a cut-off frequency of f2, and filter out the low-frequency noise and high-frequency noise outside the signal range of the input signal. The allowed passing frequency is f2 < f < f1, and the filtered signal will pass through the instrumentation amplifier and achieve rail-to-rail output of the signal; Step 5: After the signal comes out of the instrumentation amplifier, on the one hand, the signal will enter the converter. According to the calculation formula of the converter: When Vin inputs an AC signal, after internal processing of the converter, the DC voltage Vout is calculated; Step 6: On the other hand, the signal will enter the hysteresis comparison circuit. The signal input from the inverting input terminal of PIN_2 of the comparator is compared with the non-inverting input terminal. At this time, a fixed comparison voltage of 0.5509V is set at the non-inverting input terminal of the comparator. This voltage is pulled up to 3V3 through the R101 = 4.99K resistor and pulled down to GND through the R104 = 1K resistor. After voltage division of 3V3, the voltage Vin_compare entering the non-inverting input terminal PIN_5 of the operational amplifier at this moment is: And based on the principle of the voltage follower of the operational amplifier, the voltage at the inverting input terminal PIN_6 of the operational amplifier will be equal to the voltage at the non-inverting input PIN_5, so that the fixed comparison voltage at the non-inverting input terminal of the comparator is Vin_compare. Therefore, Vin_compare will be compared with the signal input from the inverting input terminal of PIN_2 of the comparator, thereby determining the flip voltage of the output pin PIN_1 of the comparator. The high level is the pull-up voltage of 3V3, and the low level is 0V. And this changing level signal is input to the main control MCU for input capture through the timer; Step 7: Through the analysis and calculation in Steps 1 to 6, the root mean square value Vrms of the audio signal of the audio amplifier can be obtained, that is, the test item SPKR_R_OUT_P_N_RMS_mV. The input voltage of PIN_2 (IN2) of the converter is half of the 5V voltage division, that is, 2.5V, and the PIN_6 pin (OUT RTN) is connected to GND, so OUT RIN = 0. And the peak-to-peak voltage input to PIN_2 (IN1) of the converter has been calculated as Vp-p = 2.983V in Step 4. Then the peak voltage is theoretically calculated as Vp, Therefore, the converter's PIN_2 input IN1 = Vp = 1.491V, and the Vrms value can be calculated based on the formula theory as follows: That is, the test item SPKR_R_OUT_P_N_RMS_mV=Vrms; Step 8. Since the operating frequency f is known, execute according to step 6. The frequency signal to be measured enters the main control MCU timer channel, and the input capture function is started. When the timer captures a high level or a low level, it will enter the interrupt capture and calculate the frequency f through the CNT count value. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 is a test signal flow chart of the present invention; Figure 2 It is a test block diagram of the present invention; Figure 3 It is the first part of the test block diagram of the present invention; Figure 4 It is the test block diagram of the second part of the present invention; Figure 5 is a circuit schematic diagram of the frequency processing board; Figure 6 is a circuit schematic diagram of the power module; Figure 7 is a circuit schematic diagram of the switching module; Figure 8 is a circuit schematic diagram of the main control board; Fig. 9 It is the block diagram of the audio module to be tested; Fig.10 is a block diagram of the main control board; Fig.11 It is a numerical table of RMS value and frequency value tested by oscilloscope; Fig.12 It is a numerical table of RMS values ​​and frequency values ​​tested using the technical solution of the present application; Fig.13 This is a diagram of machine accuracy tested using the technical solution of this application. DETAILED DESCRIPTION

[0013] like Figures 1 to 5As shown, in this embodiment, the present invention includes a main control board 1, a DMM test board 2, a frequency processing board 3, a test signal adapter board 4, and an audio module 5 to be tested. The audio module 5 to be tested is connected to the frequency processing board 3 via the test signal adapter board 4, and the frequency processing board 3 is connected to the main control board 1 via the DMM test board 2. The frequency processing board 3 is connected to the main control board 1. The frequency processing board 3 includes a converter U104, a comparator U102A, an instrument amplifier U103 and an operational amplifier U101B. The input end of the instrument amplifier U103 is connected to the audio module 5 to be tested, the IN1 end of the converter U104 is connected to the output end of the instrument amplifier U103 and the reverse input end of the comparator U102A, the VOUT end of the converter U104 is connected to the DMM test board 2, and the non-inverting input end of the comparator U102A is connected to the operational amplifier U101B.

[0014] The model of the converter U104 is LTC1968CMS8#PBF, the model of the instrument amplifier U103 is AD8220BRM, the model of the comparator U102A is LM393DR, and the model of the operational amplifier U101B is OPA2196IDGKR.

[0015] The measurement of RMS voltage and frequency refers to the operating frequency f and effective value Vrms when the test product is working normally.

[0016] The method for frequency measurement is to build a hysteresis comparator through the comparator U102A, set a 0.5V comparison voltage at the non-inverting input terminal, and use the inverting input terminal as the input signal to be compared. According to the periodic change of the input signal itself, when the inverting input terminal voltage is greater than the non-inverting input terminal voltage by 0.5V, the comparator U102A outputs a high level; when the inverting input terminal signal is lower than 0.5V, the comparator U102A outputs a low level.

[0017] The method for measuring the root mean square voltage value is to use the converter U104, an RMS to DC integrated chip, to measure the signal at the output terminal OUT_P / OUT_N of the audio module 5 to be tested. However, before the input signal enters the converter U104 for conversion, the OUT_P / OUT_N signal will first pass through the filter circuit, and the input signal will be filtered out of other low-frequency and high-frequency noises in the non-signal range. The filtered signal will pass through the JFET type high common mode instrument amplifier U103 to suppress noise and achieve rail-to-rail output of the signal. The instrument amplifier U103 supports rail-to-rail output and has high input impedance, high common mode rejection ratio and ultra-low input bias current, thereby ensuring that the input signal is not interfered with. At the same time, AD8220 has a high slew rate to improve the conversion rate, so that the signal can change rapidly and continuously without distortion. And according to the current test process, the signal of the audio module 5 to be tested is transferred to the test signal adapter board 4 through the probe needle method, and then transferred to the frequency processing board 3 through the IDC cable, and then communicated with the main control board 1. The START LIGHT main control board 1 communicates with the audio module 5 to be tested through I2S, and drives the audio module 5 to be tested by setting the LRCLK, BLCK, DIN signals, so that it can output the root mean square value and frequency value of a specific AC signal at the output terminal OUT_P / OUT_N.

[0018] like Figures 3 to 5 As shown, in this embodiment, the frequency processing board 3 also includes a mechanical relay K101 and an optocoupler switch K102, the pin3 pin and the pin6 pin of the mechanical relay K101 are respectively connected to the TP8_SPKR_R_OUT_M pin and the TP7_SPKR_R_OUT_P pin of the audio module 5 to be tested, the RMS_To_DC pin of the optocoupler switch K102 is connected to the VOUT end of the converter U104, and the DMM_Volt_P pin of the optocoupler switch K102 is connected to the corresponding pin of the DMM test board 2.

[0019] like Figures 3 to 5 As shown, in this embodiment, the frequency processing board 3 also includes a low-pass filter circuit and a high-pass filter circuit. The pin4 pin and the pin5 pin of the mechanical relay K101 are connected to the input end of the instrument amplifier U103 via the low-pass filter circuit and the high-pass filter circuit in sequence. The low-pass filter circuit includes a first inductor L102, a second inductor L104, a first capacitor C110, and a second capacitor C114. The high-pass filter circuit includes a first resistor R111, a second resistor R120, a third capacitor C105, and a fourth capacitor C117.

[0020] The method for measuring the root mean square value is to measure the signal of the output terminal OUT_P / OUT_N of the audio module 5 to be tested. First, the signal to be tested will be output from OUT_P (TP8) / OUT_N (TP7). The next step is that the output signal will pass through the filtering circuit. First, the signal passes through the low-pass filtering circuit, and the maximum cutoff frequency allowed to pass is calculated as: f1=1 / (2*pi*sqrt(LC)). Then it passes through the high-pass filtering circuit, and the minimum cutoff frequency allowed to pass is calculated as: f2=1 / (2*pi*RC). It is equivalent to passing the input signal through a bandpass filter composed of a first-order low-pass filter and a first-order high-pass filter. At the same time, after the signal is filtered by the front end, it will pass through the instrument amplifier U103 with high impedance input to enhance the power of the signal and further suppress the interference of the common-mode signal. In terms of root mean square value measurement, the signal passes through the converter U104, the frequency processing board 3 performs effective value processing, and the effective value signal is given to the DMM test board 2 for measurement, thereby realizing the measurement of the root mean square value. In terms of frequency measurement, the signal will be compared with the signal to be measured by the hysteresis comparator composed of the comparator U102A by setting a comparison voltage of 0.5V. The signal will be compared with 0.5V according to the amplitude of the signal to be measured, thereby outputting a high level 3V3 or a low level 0V, and finally giving the signal to the main control board 1 to capture the input signal, thereby realizing frequency measurement, wherein the main control board 1 is connected to an external host computer.

[0021] like Figures 8 to 10 As shown, in this embodiment, the main control board 1 includes a main control MCU U301. The model of the main control MCU U301 is STM32F103VET6.

[0022] like Fig. 9 As shown, in this embodiment, the audio module 5 to be tested includes an audio amplifier. The model of the audio amplifier is MAX98388.

[0023] like Figures 1 to 5 As shown, in this embodiment, the testing method includes the following steps: Step 1, the mechanical relay K101 sets the level state of pin8 OUTPUT_BIT14 to low level 0, and the mechanical relay K101 is normally open and closed, at this time, pin6 and pin5, pin3 and pin4 are connected; Step 2: The optocoupler switch K102 sets the level of pin8 (OUTPUT_BIT14) to low. A loop is formed between the optocoupler supply voltage and GND through the light-emitting diode, and current flows through the light-emitting diode, driving it to emit light. The emitted light is detected, causing the mechanical relay K101 to conduct between its normally open pins pin4 and pin3. After passing through the converter U104, the Vrms is converted into a DC voltage value, which is then directly fed to the ADC analog-to-digital conversion chip for acquisition. Step 3: Through I2S communication, the main control MCU, as the master, sends instructions to the audio amplifier to configure and initialize it. Key register 1: 0x2090 Setting the register write parameter refers to the speaker channel volume control. The value written to the Speaker Channel Volume Control register address 0x2090 is 0x00 (0dB) to ensure the signal is 0dB. For key register 2: 0x2092, setting the register write parameter refers to the audio amplifier output configuration. The value written to the Speaker Amplifier Output Configuration register address 0x2092 is 0x03. SPK_AMP_MODE = 0 sets the working mode to Single-cell mode (default for MAX98388), and SPK_GAIN[2:0] = 3, which means the MAX98388 is set to Single-cell Mode: 2.11VRMS (+6dB) at this time. Step 4: After the basic operation settings for initializing the audio amplifier in Step 3, through formula conversion, the Vp-p voltage of the AC signal of the audio amplifier at this time is: At this time, the Vp-p peak-to-peak voltage output from the audio signal output pins SPKR_R_OUT_P and SPKR_R_OUT_N is 2.983V. It will first pass through the low-pass filter circuit with a cut-off frequency of f1 and the high-pass filter circuit with a cut-off frequency of f2, filtering out low-frequency and high-frequency noises outside the signal range of the input signal, allowing frequencies in the range f2 < f < f1 to pass through. The filtered signal then passes through the instrumentation amplifier U103 and realizes rail-to-rail output of the signal. Step 5: After the signal comes out of the instrumentation amplifier U103, on the one hand, the signal enters the converter U104. According to the calculation formula of the converter U104: When Vin inputs an AC signal, a DC voltage Vout is calculated after internal processing by the converter U104; Step 6, on the other hand, the signal will enter the hysteresis comparison circuit, and the input signal from the inverting input terminal of the PIN_2 pin of the comparator U102A is compared with the non-inverting terminal. At this time, a fixed comparison voltage of 0.5509V is set at the non-inverting input terminal of the comparator U102A. The voltage is pulled up to 3V3 through the R101=4.99K resistor and pulled down to GND through the R104=1K resistor. After dividing the 3V3, the voltage Vin_compare entering the non-inverting input terminal PIN_5 of the operational amplifier U101B at this moment is: , And through the voltage follower principle of the operational amplifier U101B, the voltage of the inverting input terminal PIN_6 of the operational amplifier U101B will be equal to the voltage of the non-inverting input PIN_5, so that the fixed comparison voltage of the non-inverting input terminal of the comparator U102A is Vin_compare, so Vin_compare will be compared with the input signal of the inverting input terminal of the PIN_2 pin of the comparator U102A, so as to determine the flip voltage of the output pin PIN_1 of the comparator U102A, the high level is the pull-up voltage of 3V3, and the low level is 0V, and the changed level signal is input to the main control MCU for input capture through the timer; Step 7. Through the analysis and calculation of steps 1 to 6, the root mean square value Vrms of the audio signal of the audio amplifier can be obtained, that is, the test item SPKR_R_OUT_P_N_RMS_mV. The input voltage of the PIN_2 pin IN2 of the converter U104 is half of the 5V divided voltage, that is, 2.5V, and the PIN_6 pin OUT RTN is connected to GND, so OUT RIN=0. The input peak-to-peak voltage of the PIN_2 pin IN1 has been calculated as Vp-p=2.983V in Step 4, so the peak voltage is theoretically calculated as Vp, Therefore, the PIN_2 input IN1 of the converter U104 = Vp = 1.491V, and the Vrms value is calculated according to the formula theory as follows: That is, the test item SPKR_R_OUT_P_N_RMS_mV=Vrms; Step 8. Since the operating frequency f is known, execute according to step 6. The frequency signal to be measured enters the main control MCU timer channel, and the input capture function is started. When the timer captures a high level or a low level, it will enter the interrupt capture and calculate the frequency f through the CNT count value.

[0024] like Figure 6 As shown, in this embodiment, the measuring device of the audio amplifier module further includes a power supply module, and the power supply module is used to control the power supply of the system and the power supply of the key signal processing IC.

[0025] like Figure 7 As shown, in this embodiment, the frequency processing board 3 also includes a switching module, and the main function of the switching module is to realize level conversion between the audio module 5 to be tested and the main control board 1 working between different power supplies, ensuring that the level communication between them can work normally under their own working power supplies, thereby ensuring the normal operation of communication.

[0026] like Figures 1 to 5 As shown, in this embodiment, the frequency processing board 3 is involved in filtering the output signal OUT_P / OUT_N of the audio module 5 to be tested, and the signal after filtering is given to the high-precision wide-bandwidth converter U104 on the one hand; on the other hand, the signal is given to the hysteresis comparator composed of the comparator U102A, and the comparison signal is set according to the amplitude of the signal, so that the comparator U102A flips the level as the input signal changes, and then the periodically changing signal is given to the input capture of the main control board 1 to measure its frequency.

[0027] like Figures 11 to 13 As shown, in this embodiment, Fig.11 To measure 10 groups of products using an oscilloscope, the RMS value and frequency data were tested on 4 channels respectively. Fig.12 In order to measure 10 groups of products using the fixture integrated board of the present application, the data of the root mean square value and frequency are tested and measured on 4 channels respectively.

[0028] The test settings configuration parameters: IN2=2.5V, OUT RIN=0V, Vp-p=3V.

[0029] Fig.13 As shown in the figure, the oscilloscope test value is set as the measurement value of the standard instrument. Machine accuracy = | (machine test average value - oscilloscope test average value) | / oscilloscope test average value This application implements the test of RMS value and frequency. In the test between the standard instrument (oscilloscope) and the integrated board, the integrated board test not only has good consistency between multi-channel test channels, but also has higher measurement accuracy than the standard instrument oscilloscope. The performance is that the machine measurement accuracy of using 10 DUTs to test the RMS value and frequency on 4 channels is SPKR_R_OUT_P_N_Frequency / Hz / %=0.0951%, SPKR_R_OUT_P_N_RMS / mV / %=0.1504 / %. In this regard, the design of the integrated board not only realizes the high-precision measurement of RMS value and frequency, but also plays the role of replacing instruments and equipment, thereby saving costs and meeting customer needs. This also reflects that in the field of testing, the use of innovative measurement solutions can reduce costs and increase efficiency when solving testing problems, and improve the competitiveness of technology.

[0030] Although the embodiments of the present invention are described with practical solutions, they do not constitute limitations on the meaning of the present invention. For those skilled in the art, it is obvious to modify the implementation scheme and combine it with other solutions based on this description.

Claims

1. A measuring device for an audio amplifier module, characterized in that: The invention comprises a main control board (1), a DMM test board (2), a frequency processing board (3), a test signal adapter board (4), and an audio module to be tested (5). The audio module to be tested (5) is connected to the frequency processing board (3) via the test signal adapter board (4). The frequency processing board (3) is connected to the main control board (1) via the DMM test board (2). The frequency processing board (3) is connected to the main control board (1). The frequency processing board (3) comprises a converter (U104), a comparator (U102A), and an instrument. An amplifier (U103) and an operational amplifier (U101B), wherein the input end of the instrument amplifier (U103) is connected to the audio module (5) to be tested, the IN1 end of the converter (U104) is connected to the output end of the instrument amplifier (U103) and the reverse input end of the comparator (U102A), the VOUT end of the converter (U104) is connected to the DMM test board (2), and the non-inverting input end of the comparator (U102A) is connected to the operational amplifier (U101B).

2. The measuring device of an audio amplifier module according to claim 1, characterized in that: The frequency processing board (3) further comprises a mechanical relay (K101) and an optocoupler switch (K102); the pin3 and pin6 of the mechanical relay (K101) are respectively connected to the TP8_SPKR_R_OUT_M and TP7_SPKR_R_OUT_P pins of the audio module (5) to be tested; the RMS_To_DC pin of the optocoupler switch (K102) is connected to the VOUT terminal of the converter (U104); and the DMM_Volt_P pin of the optocoupler switch (K102) is connected to the corresponding pin of the DMM test board (2).

3. The measuring device of an audio amplifier module according to claim 2, characterized in that: The frequency processing board (3) further comprises a low-pass filter circuit and a high-pass filter circuit. Pin 4 and pin 5 of the mechanical relay (K101) are connected to the input end of the instrument amplifier (U103) via the low-pass filter circuit and the high-pass filter circuit respectively. The low-pass filter circuit comprises a first inductor (L102), a second inductor (L104), a first capacitor (C110), and a second capacitor (C114). The high-pass filter circuit comprises a first resistor (R111), a second resistor (R120), a third capacitor (C105), and a fourth capacitor (C117).

4. The measuring device for an audio amplifier module according to claim 3, characterized in that: The main control board (1) comprises a main control MCU (U301).

5. The measuring device for an audio amplifier module according to claim 4, characterized in that: The audio module (5) to be tested includes an audio amplifier.

6. A method for testing the measuring device of the audio amplifier module as claimed in claim 5, characterized in that: The test method comprises the following steps: Step 1, the mechanical relay (K101) sets the level state of pin8 OUTPUT_BIT14 to low level 0, and the mechanical relay (K101) is normally open and closed, at which time pin6 and pin5, pin3 and pin4 are connected; Step 2: The opto-coupler switch (K102) sets the level of pin8 OUTPUT_BIT14 to low. A loop is formed between the opto-coupler supply voltage and GND through the light-emitting diode, and current flows through the light-emitting diode, driving the light-emitting diode to emit light. The emitted light is detected, causing the mechanical relay (K101) to conduct between its normally open pins pin4 and pin3. The signal passes through the converter (U104), which converts Vrms into a DC voltage value, and then the DC voltage value is directly fed to the ADC analog-to-digital conversion chip for acquisition. Step 3: Through I2S communication, the main control MCU, acting as the master, sends instructions to the audio amplifier to perform configuration initialization. For key register 1: 0x2090, the register write parameter setting refers to the speaker channel volume control. The value written to the Speaker Channel Volume Control register address: 0x2090 is set to 0x00 (0dB) to ensure the signal is 0dB. For key register 2: 0x2092, the register write parameter setting refers to the audio amplifier output configuration. The value written to the Speaker Amplifier Output Configuration register address: 0x2092 is set to 0x03. SPK_AMP_MODE = 0 sets the operating mode to: Single-cell mode (default for MAX98388), and SPK_GAIN[2:0] = 3, which means that MAX98388 is set to Single-cell Mode: 2.11VRMS (+6dB) at this time. Step 4: After the basic operation settings for initializing the audio amplifier in Step 3, through formula conversion, the Vp-p voltage of the AC signal of the audio amplifier at this time is: At this time, the Vp-p peak-to-peak voltage output from the audio signal output pins SPKR_R_OUT_P and SPKR_R_OUT_N is 2.983V. It will first pass through the low-pass filter circuit with a cut-off frequency of f1 and the high-pass filter circuit with a cut-off frequency of f2, filtering out low-frequency and high-frequency noises outside the signal range of the input signal. The allowed frequency range is f2 < f < f1. The filtered signal then passes through the instrumentation amplifier (U103), and a rail-to-rail output of the signal is achieved. Step 5: After the signal comes out of the instrument amplifier (U103), the signal will enter the converter (U104). According to the calculation formula of the converter (U104): When an AC signal is input to Vin, a DC voltage Vout is calculated after internal processing of the converter (U104); Step 6. On the other hand, the signal will enter the hysteresis comparison circuit, and the input signal from the inverting input terminal of the PIN_2 pin of the comparator (U102A) will be compared with the non-inverting terminal. At this time, a fixed comparison voltage of 0.5509V is set at the non-inverting input terminal of the comparator (U102A). The voltage is pulled up to 3V3 through the R101=4.99K resistor and pulled down to GND through the R104=1K resistor. After dividing the 3V3, the voltage Vin_compare entering the non-inverting input terminal PIN_5 of the operational amplifier (U101B) is: , And through the voltage follower principle of the operational amplifier (U101B), the voltage of the inverting input terminal PIN_6 of the operational amplifier (U101B) will be equal to the voltage of the non-inverting input PIN_5, so that the fixed comparison voltage of the non-inverting input terminal of the comparator (U102A) is Vin_compare, so Vin_compare will be compared with the input signal of the inverting input terminal of the PIN_2 pin of the comparator (U102A), so as to determine the flip voltage of the output pin PIN_1 of the comparator (U102A), the high level is the pull-up voltage of 3V3, and the low level is 0V, and the changed level signal is input to the main control MCU for input capture through the timer; Step 7. Through the analysis and calculation of steps 1 to 6, the root mean square value Vrms of the audio signal of the audio amplifier can be obtained, that is, the test item SPKR_R_OUT_P_N_RMS_mV. The input voltage of the PIN_2 pin IN2 of the converter (U104) is half of the 5V divided voltage, that is, 2.5V, and the PIN_6 pin OUT RTN is connected to GND, so OUT RIN=0, and the input peak-to-peak voltage of the PIN_2 pin IN1 has been calculated as Vp-p=2.983V in Step 4, so the peak voltage is theoretically calculated as Vp, Therefore, the PIN_2 input IN1 of the converter (U104) = Vp = 1.491V, and the Vrms value is calculated according to the formula theory as follows: That is, the test item SPKR_R_OUT_P_N_RMS_mV=Vrms; Step 8. Since the operating frequency f is known, execute according to step 6. The frequency signal to be measured enters the main control MCU timer channel, and the input capture function is started. When the timer captures a high level or a low level, it will enter the interrupt capture and calculate the frequency f through the CNT count value.

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