A kind of end-stage voltage tracking anti-clipping circuit for audio power amplifier

Abstract

The application discloses a kind of end-stage voltage tracking anti-clipping circuits for audio power amplifier, it is related to power amplifier technical field, the circuit includes: voltage dividing circuit: for receiving from target power amplifier device and end-stage voltage and generating combination voltage signal;Audio attenuation module: for receiving audio input signal and end-stage voltage, whether to receive start signal discrimination whether to perform amplitude modulation to audio input signal after completing power output;Start discrimination module: for receiving combination voltage signal and first output signal, combination voltage signal is compared with first output signal to generate start signal.The application sets the end-stage voltage of the collected target power amplifier as a dynamic amplitude limiting threshold, which can quickly suppress excessively high signals to a safe range when the power supply momentarily drops, thereby avoiding the degradation of listening experience caused by waveform truncation of the power amplifier signal and avoiding the safety hazards caused by amplitude clipping.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of power amplifier, in particular to a kind of final stage voltage tracking anti clipping circuit for audio power amplifier. BACKGROUND

[0002] The peak factor of audio signal refers to the ratio of the peak value to the effective value of the audio signal. Sound signals usually have a large peak factor. The peak factor of language is about 12dB, and the peak factor of music can be as high as 20dB. Therefore, the amplitude of audio signal is far below the peak value most of the time. Due to the large amplitude fluctuation range of audio signal, the working voltage of power amplifier cannot be set high enough to avoid clipping due to cost, efficiency and other factors. Once clipping occurs, it will not only worsen the listening experience, but also damage the speaker. Therefore, it is necessary to limit the peak value of audio signal before it is sent to the power amplifier.

[0003] The existing limiter usually sets a fixed threshold. When the input audio signal exceeds the threshold, it is compressed to the threshold, so that the signal sent to the power amplifier circuit is below the threshold, thereby reducing the risk of clipping. This processing method does not consider the problem of unstable power amplifier final stage voltage. When the final stage voltage decreases, clipping problem still occurs. In actual application, there are many factors that cause the voltage of the final stage power amplifier to be unstable, such as power grid voltage fluctuation, power amplifier load change, music signal peak factor change, etc. It is common that the voltage decreases by 30%. In this extreme case of large power supply voltage drop, the existing technology is prone to clipping distortion. Even if the amplitude of the input audio signal is well limited, the output will still have serious clipping, which not only affects the sound quality, but also poses a safety problem to the speaker. SUMMARY

[0004] The present application aims to provide a kind of final stage voltage tracking anti clipping circuit for audio power amplifier, solve the problem that the existing power amplifier technology is prone to clipping distortion and difficult to balance the sound quality of power amplifier audio signal and the stability of power amplifier equipment when facing voltage drop.

[0005] The present application is realized by the following technical scheme:

[0006] A kind of final stage voltage tracking anti clipping circuit for audio power amplifier, the circuit includes:

[0007] The voltage dividing circuit is used to receive the first final stage voltage and the second final stage voltage from the target power amplifier device, input the first final stage voltage and the second final stage voltage to the audio attenuation module at the same time, and input the first final stage voltage and the second final stage voltage to the start-up discrimination module in the form of combined voltage signal.

[0008] The audio attenuation module is configured to receive an audio input signal from the target power amplifier device, the first end voltage and the second end voltage, and a start signal from the start discrimination module. When the start signal is received and the amplitude of the audio input signal exceeds the first end voltage and the second end voltage, the audio attenuation module performs amplitude limiting modulation on the audio input signal to generate a first output signal representing the output of the power amplifier. When the start signal is not received, the audio attenuation module outputs the audio input signal as a second output signal.

[0009] The start discrimination module is configured to receive the combined voltage signal and the first output signal, and compare the combined voltage signal as a reference voltage threshold with the first output signal. When the voltage of the first output signal is higher than the reference voltage threshold, the start discrimination module outputs a start signal to start the amplitude limiting modulation of the audio attenuation module. When the voltage of the first output signal is lower than the reference voltage threshold, the start discrimination module does not output the start signal.

[0010] The first end voltage represents the positive end voltage of the target power amplifier device, and the second end voltage represents the negative end voltage of the target power amplifier device.

[0011] Further, the start discrimination module comprises a discrimination output end, a first discrimination input end and a second discrimination input end, and the audio attenuation module comprises an attenuation input end, an attenuation output end and an enable end for receiving the start signal. The first output signal is input to the first discrimination input end of the start discrimination module, and the combined voltage signal generated by the voltage dividing circuit is input to the second discrimination input end of the start discrimination module. The discrimination output end of the start discrimination module is connected to the enable end of the audio attenuation module.

[0012] Further, the audio attenuation module comprises an audio linear attenuation circuit and a running module with an enable end. The audio linear attenuation circuit receives the audio input signal, the first end voltage and the second end voltage, and the running module receives the start signal. The audio linear attenuation circuit and the running module are signal-connected. The input end of the audio linear attenuation circuit is configured as the attenuation input end for receiving the audio input signal, and the output end of the audio linear attenuation circuit is configured as the attenuation output end for generating the first output signal.

[0013] The audio linear attenuation circuit comprises:

[0014] The sampling branch is configured to collect the first end voltage and the second end voltage from the target power amplifier device to form a positive-negative symmetrical power supply voltage, which is used as a reference voltage for amplitude limiting modulation of the audio input signal.

[0015] The main control circuit is used for receiving an audio input signal, obtaining reference values of the first and second final stage voltages received by the sampling branch and comparing with the audio input signal, when the audio input signal is higher than the reference values, adjusting the voltage value of the charge and discharge in the conduction loop, so that the voltage value of the audio input signal is amplitude modulated, and then generating a first output signal; when the audio input signal is lower than the reference values, outputting the audio input signal as a second output signal.

[0016] Further, the main control circuit comprises a first amplifier U1, a first field effect transistor Q1, a first resistor R1, a second resistor R2, a third resistor R3, a fifth resistor R5, a sixth resistor R6, a first capacitor C1, a first comparator Y1 and a second comparator Y2, wherein the first field effect transistor Q1 is an N-channel field effect transistor.

[0017] One end of the first resistor R1 is set as an attenuation input end AIN, and the other end is connected to the same point as one end of the second resistor R2 and one end of the fourth resistor R4; the other end of the second resistor R2 is connected to the same point as one end of the third resistor R3 and the non-inverting input end of the first amplifier U1; the other end of the fourth resistor R4 is connected to the S pole of the first field effect transistor Q1; the D pole of the first field effect transistor Q1 is grounded, and the G pole is connected to the same point as one end of the first capacitor C1, one end of the fifth resistor R5 and one end of the sixth resistor R6; the other end of the sixth resistor R6 is connected to the other end of the first capacitor C1 at the same point, and a negative voltage VEE is set at the point; the other end of the fifth resistor R5 is connected to the same point as the output end of the first comparator Y1 and the output end of the second comparator Y2 through an inverter; the inverting input end of the first comparator Y1 and the non-inverting input end of the second comparator Y2 are respectively connected to the sampling branch.

[0018] Further, the sampling branch of the first comparator Y1 comprises a seventh resistor R7 and an eighth resistor R8; one end of the seventh resistor R7 is connected to the first final stage voltage VP, the other end of the seventh resistor R7 is connected to the same point as one end of the eighth resistor R8 and the non-inverting input end of the first comparator Y1, and the other end of the eighth resistor R8 is grounded.

[0019] Further, the sampling branch of the second comparator Y2 comprises a ninth resistor R9 and a tenth resistor R10; one end of the ninth resistor R9 is connected to the second final stage voltage VN, the other end of the ninth resistor R9 is connected to the same point as one end of the tenth resistor R10 and the non-inverting input end of the second comparator Y2, and the other end of the tenth resistor R10 is grounded.

[0020] Further, the start-up discrimination module comprises a follower circuit, a frequency compensation circuit and a comparator unit, the first output signal is input to the follower circuit, and the combined voltage signal is input to the comparator unit;

[0021] The follower circuit is used to amplify weak signals and keep voltage following while eliminating the distorted amplitude of the first output signal using low output impedance; the frequency compensation circuit is used to suppress high-frequency noise and keep the signal strength of the first output signal transmitted by the follower circuit; the comparator unit is used to receive the combined voltage signal, perform voltage comparison between the combined voltage signal as a reference voltage threshold and the first output signal, and the output end of the comparator unit is set as the output end of the start-up discrimination module for outputting the start-up signal.

[0022] Further, the follower circuit comprises an eleventh resistor R11, a second capacitor C2 and a second amplifier U2, one end of the eleventh resistor R11 and the non-inverting input end of the second amplifier U2 are connected to the same point, and the point is set as the first discrimination input end BIN; the other end of the eleventh resistor R11 is connected to the second capacitor C2 and the positive power supply end of the second amplifier U2 in sequence, and the negative power supply end of the second amplifier U2 is grounded; the inverting input end of the second amplifier U2 and the output end of the second amplifier U2 are connected to the same point and set as the end point E1, and the end point E1 is represented as the output end of the follower circuit and the input end of the frequency compensation circuit.

[0023] Further, the frequency compensation circuit comprises a thirteenth resistor R13, a fourteenth resistor R14, a fifteenth resistor R15, a sixteenth resistor R16, a third capacitor C3, a first inductor L1 and a third amplifier U3;

[0024] One end of the sixteenth resistor R16 and one end of the thirteenth resistor R13, and the inverting input end of the third amplifier U3 are all connected to the end point E1, and the other end of the thirteenth resistor R13 is grounded, and the non-inverting input end of the third amplifier U3 is connected to the reference voltage Vref; the other end of the sixteenth resistor R16 and one end of the fourteenth resistor R14 and one end of the first inductor L1 are connected to the same point, and the point is provided with the first positive voltage VCC1; the other end of the fourteenth resistor R14 is connected to the third capacitor C3 and the ground in sequence; the other end of the first inductor L1 is connected to one end of the fifteenth resistor R15, and the other end of the fifteenth resistor R15 and the output end of the third amplifier U3 are connected to the same point and set as the end point E2, and the end point E2 is represented as the output end of the frequency compensation circuit and the input end of the comparator unit.

[0025] Further, the comparator unit includes a twelfth resistor R12, a third comparator Y3, and a fourth capacitor C4; the non-inverting input of the third comparator Y3 is connected to terminal E2, the inverting input of the third comparator Y3 is connected to one end of the twelfth resistor R12, and the other end of the twelfth resistor R12 is set as the second discrimination input CIN; the negative power supply terminal of the third comparator Y3 is grounded, the positive power supply terminal of the third comparator Y3 and one end of the fourth capacitor C4 are connected to the same point and a second positive voltage VCC2 is set at that point, and the other end of the fourth capacitor C4 is grounded; the output terminal of the third comparator Y3 is set as the discrimination output BOUT.

[0026] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0027] 1. It can sample and divide the final stage voltage of the positive and negative terminals of the target power amplifier in real time and use it as a dynamic limiting threshold. It can automatically adjust the limiting threshold with power fluctuations. When the power drops instantaneously, the limiting module can quickly intervene to effectively suppress the excessively high signal to a safe range, which can avoid the spectral distortion and deterioration of the listening experience caused by the truncation of the power amplifier signal waveform.

[0028] 2. By activating limiting on demand, limiting modulation is only activated when the audio signal level exceeds the power supply capacity. This ensures that there is no need to suppress the signal when the voltage is sufficient, thus preserving the dynamics and details of the sound. When the voltage is insufficient, it intervenes in time, without sacrificing clarity, and protects the speakers and amplifier components from damage due to overload.

[0029] 3. The voltage divider, comparator, and attenuation modules use a loosely coupled design, which allows the circuit modules to monitor the power supply status in real time. Compared with single-rail detection, this reduces the frequent activation of power amplifier bootstrap and overcurrent protection caused by voltage fluctuations, and lowers the risk of sudden silence or restart caused by the intervention of protection circuits. Attached Figure Description

[0030] The accompanying drawings, which are included to provide a further understanding of embodiments of the invention and form part of this application, do not constitute a limitation thereof. In the drawings:

[0031] Figure 1 This is a schematic diagram of the structure of the present invention;

[0032] Figure 2 This is a schematic diagram of the composition structure of the audio attenuation module of the present invention;

[0033] Figure 3 This is a schematic diagram of the circuit structure of the audio linear attenuation circuit of the present invention;

[0034] Figure 4 This is a schematic diagram of the circuit structure of the startup discrimination module of the present invention. DETAILED DESCRIPTION

[0035] In order to make the objectives, technical solutions and advantages of the present application clearer, further detailed description will be made to the present application in combination with embodiments and drawings, the illustrative embodiments of the present application and the description thereof are only used to explain the present application, and do not serve as limitation to the present application.

[0036] Embodiment 1

[0037] As shown in the figure, the embodiment is a kind of end-stage voltage tracking anti-clipping circuit for audio power amplifier, the circuit comprises: Figure 1

[0038] voltage dividing circuit: for receiving first end-stage voltage and second end-stage voltage from target power amplifier device, simultaneously inputting first end-stage voltage and second end-stage voltage to audio attenuation module, and inputting the first end-stage voltage and second end-stage voltage in the form of combined voltage signal to start-up discrimination module;

[0039] audio attenuation module: for receiving audio input signal, first end-stage voltage and second end-stage voltage from target power amplifier device, start-up signal from start-up discrimination module, when receiving start-up signal, and audio input signal amplitude exceeds first end-stage voltage and second end-stage voltage, then amplitude modulation is generated to audio input signal to generate first output signal representing power amplifier output, when not receiving start-up signal, audio input signal is represented as second output signal output;

[0040] start-up discrimination module: for receiving combined voltage signal and first output signal, combined voltage signal is compared with first output signal as reference voltage threshold, when first output signal voltage is higher than reference voltage threshold, start-up discrimination module outputs start-up signal to start amplitude modulation of audio attenuation module, when first output signal voltage is lower than reference voltage threshold, start-up discrimination module does not output start-up signal;

[0041] Wherein, the first end-stage voltage represents the end-stage positive power supply voltage of target power amplifier device, and the second end-stage voltage represents the end-stage negative power supply voltage of target power amplifier device;The start-up discrimination module comprises discrimination output end, first discrimination input end and second discrimination input end, and the audio attenuation module comprises attenuation input end, attenuation output end and enable end for receiving start-up signal;The first output signal is input to the first discrimination input end of start-up discrimination module, and the combined voltage signal generated by the voltage dividing circuit is input to the second discrimination input end of start-up discrimination module, and the discrimination output end of the start-up discrimination module is connected to the enable end of the audio attenuation module.

[0042] ​The audio input signal represents an audio source signal played by a target power amplifier device. The first final stage voltage represents a positive power supply rail voltage of a power amplifier of the target power amplifier device, and the second final stage voltage represents a negative power supply rail voltage of the power amplifier of the target power amplifier device, which determines a maximum output swing range of the power amplifier, for example, a signal output can be from -150V to +150V, which can be used in a professional high-power application, and clipping will occur if the signal output exceeds the range. The first final stage voltage and the second final stage voltage received by the input end of the voltage dividing circuit are connected to the output end of the starting discrimination module; the voltage dividing circuit is used to collect the first final stage voltage and the second final stage voltage of the target power amplifier, and generate a combined voltage output to the starting discrimination module as a threshold voltage for amplitude limiting; the real power supply capability of the power amplifier is mapped to a reference amplitude limiting level threshold, and a voltage signal required by the amplitude limiting reference and attenuation module is provided. The attenuation input end of the audio attenuation module receives the audio input signal, and the attenuation output end generates a first output signal; the audio attenuation module is used to control whether to limit the amplitude of the audio signal according to real-time voltage information or to transmit the audio signal directly when the comparator is enabled by starting the amplitude limiting process. When the starting signal of the starting discrimination module is received, the enable end of the audio attenuation module receives the starting signal at this time, that is, the port is at a valid level, and the audio attenuation module calculates the maximum allowable output level in real time according to the first final stage voltage and the second final stage voltage, performs dynamic compression or clipping on the audio input signal, and outputs the amplitude-limited signal. When the starting signal of the starting discrimination module is not received, the receiving state of the enable end is invalid at this time, the audio attenuation module directly outputs the audio input signal as a second output signal without amplitude limiting, that is, the second output signal is equivalent to the signal itself when the first output signal is below the reference voltage threshold. Therefore, the first output signal can be kept in a relatively stable parameter range through the amplitude modulation of the audio attenuation module. The first discrimination input end of the starting discrimination module is used to receive the first output signal, the second discrimination input end is used to receive the combined voltage signal, and the discrimination output end outputs a starting signal; the output audio level is compared with the reference voltage to determine whether to start the attenuation and output the starting signal. The working mode of the starting discrimination module is two: either outputting the starting signal to enable the enable end of the audio attenuation module, so that the audio attenuation module enters a working state of judging whether to perform amplitude limiting; or not outputting the starting signal to disable the enable end, so that the audio attenuation module does not perform amplitude limiting. If the starting discrimination module determines that amplitude limiting is needed, but the audio attenuation module determines that the audio input signal is below the reference value of the first final stage voltage and the second final stage voltage, then the amplitude limiting is not performed. That is, the starting discrimination module performs first-order discrimination, and the audio attenuation module performs second-order discrimination, so as to confirm whether the audio input signal needs to be amplitude limited in a double-discrimination manner, so as to ensure the precision of the audio input signal processing.In practical implementation, the voltage divider circuit can be set up in a variety of conventional ways. The simplest and lowest cost way is to set up a resistor voltage divider network, that is, after setting voltage divider resistors on the independent branches of the first final stage voltage and the second final stage voltage, the two lines are directly connected together for output. If the system has higher requirements for accuracy or anti-interference, existing differential amplifiers or operational amplifiers can also be used to set up a voltage distribution network as a voltage divider circuit structure.

[0043] Example 2

[0044] like Figure 2 As shown, in this embodiment, the audio attenuation module includes an audio linear attenuation circuit and an operating module with an enable terminal. The audio linear attenuation circuit receives an audio input signal, a first final stage voltage, and a second final stage voltage. The operating module receives a start signal, and the audio linear attenuation circuit and the operating module maintain a signal connection. The input terminal of the audio linear attenuation circuit is configured as an attenuation input terminal for receiving the audio input signal, and the output terminal of the audio linear attenuation circuit is configured as an attenuation output terminal for generating a first output signal.

[0045] The audio linear attenuation circuit includes:

[0046] Sampling branch: Used to collect and receive the first and second final stage voltages from the target power amplifier device, forming a positive and negative symmetrical power supply voltage, which is used as a reference voltage for limiting and modulating the audio input signal;

[0047] Main control circuit: Used to receive audio input signal, obtain reference values ​​of the first and second final stage voltages received by the sampling branch and compare them with the audio input signal. When the audio input signal is higher than the reference value, the charging and discharging voltage value in the conduction circuit is adjusted so that the voltage value of the audio input signal is limited and modulated, and then the first output signal is generated. When the audio input signal is lower than the reference value, the audio input signal is output as the second output signal.

[0048] The function of the operating module is to determine whether to activate the audio linear attenuation circuit based on the received activation signal. If the audio linear attenuation circuit is activated, the audio input signal is limited; otherwise, the audio input signal is directly output as the second output signal. In this embodiment, conventional valid level logic is used, meaning the valid level of the enable terminal of the operating module is set to high by default. In practical applications, the operating module can use transistors or field-effect transistors as switching elements. For example, a transistor can be used as a start switch; when the activation judgment module outputs a high level, it drives the transistor to conduct, thereby activating the audio linear attenuation circuit. Alternatively, logic gates can be used to construct a level switch to directly activate the audio linear attenuation circuit.

[0049] Further, as shown in Figure 3 as a feasible implementation, the main control circuit comprises a first amplifier U1, a first field effect transistor Q1, a first resistor R1, a second resistor R2, a third resistor R3, a fifth resistor R5, a sixth resistor R6, a first capacitor C1, a first comparator Y1 and a second comparator Y2, wherein the first field effect transistor Q1 is an N-channel field effect transistor;

[0050] One end of the first resistor R1 is set as an attenuated input end AIN, and the other end is connected to the same point as one end of the second resistor R2 and one end of the fourth resistor R4; the other end of the second resistor R2 is connected to the same point as one end of the third resistor R3 and the non-inverting input end of the first amplifier U1; the other end of the fourth resistor R4 is connected to the S pole of the first field effect transistor Q1; the D pole of the first field effect transistor Q1 is grounded, and the G pole is connected to the same point as one end of the first capacitor C1, one end of the fifth resistor R5 and one end of the sixth resistor R6; the other end of the sixth resistor R6 is connected to the same point as the other end of the first capacitor C1, and a negative voltage VEE is set at the point; the other end of the fifth resistor R5 is connected to the same point as the output end of the first comparator Y1 and the output end of the second comparator Y2 through an inverter; the non-inverting input end of the first comparator Y1 and the inverting input end of the second comparator Y2 are respectively connected to a sampling branch.

[0051] The first resistor R1, the second resistor R2 and the third resistor R3 form a voltage division feedback network of the first amplifier U1, and form a voltage division buffer with a gain less than 1 to correct the level of the audio input signal. The first amplifier U1 is used as an integrated operational amplifier to provide a low distortion and low output impedance buffer; the output of the first amplifier U1 is directly fed into the control node of the first field effect transistor Q1, and the input terminals of the first comparator Y1 and the second comparator Y2. The first field effect transistor Q1 is used as a current limiting control element to adjust the discharge level of the audio signal to the ground, and to complete linear attenuation. The first field effect transistor Q1 is a junction field effect transistor, and the on-resistance of the first field effect transistor Q1 is controlled by the output voltage of the charging and discharging circuit formed by the fifth resistor R5, the sixth resistor R6 and the first capacitor C1. The on-resistance of the first field effect transistor Q1 is in a positive proportional relationship with the control voltage, and the linear attenuation function of the audio signal is realized. The fourth resistor R4 guides the attenuated audio level into the first field effect transistor Q1 to determine the maximum allowed current. The first resistor R1 is a current limiting resistor, and the value of the first resistor R1 can be between 2-10kΩ. The second resistor R2 and the fourth resistor R4 are shunt resistors, and the values of the second resistor R2 and the fourth resistor R4 can be between 100-1000Ω. The above resistance values are conventional empirical values, and can be adjusted according to actual conditions. The fifth resistor R5, the sixth resistor R6 and the first capacitor C1 form a charging and discharging circuit to set the start and release times of the audio linear attenuation circuit. The first comparator Y1 and the second comparator Y2 are cross-configured to form a window comparator with hysteresis. When the output value of the first amplifier U1 output to the attenuation output terminal AOUT is greater than the upper threshold value of the final voltage sampling from the sampling branch, the first comparator Y1 pulls up to enable the first field effect transistor Q1, the voltage at the gate of the first field effect transistor Q1 is raised, the on-resistance of the first field effect transistor Q1 is reduced, the fourth resistor R4 divides part of the current of the second resistor R2, and the voltage of the attenuation output terminal AOUT is reduced. Finally, the voltage of the attenuation output terminal AOUT is dynamically controlled near the sampling voltage value of the sampling branch.

[0052] When the output value of the first amplifier U1 output to the attenuation output terminal AOUT is less than the lower threshold value, the second comparator Y2 pulls down to close the first field effect transistor Q1, and the limiting amplitude attenuation processing is not performed. In this way, the voltage of the audio input signal is monitored twice. If the start discrimination module determines that limiting amplitude processing is required, but the result of the audio linear attenuation circuit is that the audio input signal is lower than the reference value from the sampling branch, the limiting amplitude processing is not performed, and the audio input signal is output from the attenuation output terminal AOUT of the audio linear attenuation circuit and represented as a second output signal. If the start discrimination module determines that limiting amplitude processing is not required, the audio input signal does not enter the audio linear attenuation circuit, and is directly output from the audio attenuation module and represented as a second output signal.

[0053] Further, as a feasible implementation, the sampling branch of the first comparator Y1 comprises a seventh resistor R7 and an eighth resistor R8; one end of the seventh resistor R7 is connected to the first final voltage VP, the other end of the seventh resistor R7 and one end of the eighth resistor R8 are connected to the same point of the non-inverting input terminal of the first comparator Y1, and the other end of the eighth resistor R8 is grounded; the sampling branch of the second comparator Y2 comprises a ninth resistor R9 and a tenth resistor R10; one end of the ninth resistor R9 is connected to the second final voltage VN, the other end of the ninth resistor R9 and one end of the tenth resistor R10 are connected to the same point of the non-inverting input terminal of the second comparator Y2, and the other end of the tenth resistor R10 is grounded.

[0054] The seventh resistor R7 and the eighth resistor R8 constitute a first final voltage VP sampling circuit representing the positive power supply voltage of the final power amplifier; the ninth resistor R9 and the tenth resistor R10 constitute a second final voltage VN sampling circuit representing the negative power supply voltage of the final power amplifier. In this embodiment, the seventh resistor R7 and the tenth resistor R10 have the same resistance value, and the eighth resistor R8 and the ninth resistor R9 have the same resistance value, so that the sampled voltage is symmetrical in positive and negative directions, which can be about ±3V, and can be adjusted according to actual conditions. In this way, the sampling voltages of the first final voltage VP and the second final voltage VN serve as the reference signals for comparison.

[0055] Embodiment 3

[0056] In this embodiment, the start-up discrimination module comprises a follower circuit, a frequency compensation circuit and a comparator unit, the first output signal is input to the follower circuit, and the combined voltage signal is input to the comparator unit.

[0057] The follower circuit is used to amplify weak signals and maintain voltage following, while using low output impedance to eliminate the distorted amplitude of the first output signal; the frequency compensation circuit is used to suppress high-frequency noise and maintain the signal strength of the first output signal transmitted by the follower circuit; the comparator unit is used to receive the combined voltage signal, perform voltage comparison between the combined voltage signal as a reference voltage threshold and the first output signal, and the output end of the comparator unit is set as the output end of the start-up discrimination module for outputting the start-up signal.

[0058] The follower circuit receives the first output signal from the audio attenuation module, and performs voltage amplification and high-precision following on the weak signal, ensures the consistency of the signal level in the comparison of the later stage, and provides low output impedance to eliminate the amplitude distortion and signal attenuation caused by the load or the line. The frequency compensation circuit performs high-frequency suppression on the audio signal output by the follower, filters out the spikes, radio frequency interference and other high-frequency noise in the comparison process, and maintains the strength and purity of the signal to provide clean trigger input for the comparator. The comparator unit receives the first output signal after frequency compensation and the combined voltage signal from the voltage dividing circuit, compares the voltages of the two signals, and outputs the start signal when the first output signal is greater than the combined voltage signal, otherwise, no start signal is output, and the unstarted state is maintained. The start signal is directly connected to the enable end of the audio attenuation module to complete the closed-loop control.

[0059] It should be noted that the first discrimination input end receives the first output signal of the audio attenuation module, that is, the audio signal after amplitude limiting or direct transmission; the second discrimination input end receives the combined voltage signal output by the voltage dividing circuit; the discrimination output end is used to output a high-level start signal when the voltage of the audio input signal is greater than the combined voltage signal; otherwise, a low-level signal is output. The final stage of the power amplifier is usually differentially supplied or independently supplied by the left and right channels. Since the supply voltage may fluctuate due to the load, power supply, temperature and other factors, a real-time and effective reference voltage is needed, that is, the current audio input signal should not exceed the reference voltage, otherwise there is a risk of clipping. The first final stage voltage and the second final stage voltage respectively represent the positive and negative power supply rails or the voltages of the two symmetrical channels, and the combined voltage signal is generated as the reference upper limit or envelope limiting level for audio amplitude limiting. In specific implementation, the combined voltage value can be set to the absolute maximum value or the weighted average value. The audio input signal is output as the first output signal for driving the power amplifier through the audio attenuation module. The first output signal is compared with the combined voltage signal through the comparator.

[0060] Further, as shown in Figure 4 As a feasible implementation, the follower circuit includes an eleventh resistor R11, a second capacitor C2 and a second amplifier U2, one end of the eleventh resistor R11 is connected to the same point as the non-inverting input end of the second amplifier U2, and the point is set as the first discrimination input end BIN; the other end of the eleventh resistor R11 is connected in series with the second capacitor C2 and the positive power supply end of the second amplifier U2 in sequence, and the negative power supply end of the second amplifier U2 is grounded; the inverting input end of the second amplifier U2 is connected to the same point as the output end of the second amplifier U2, and the point is set as the end point E1, which is represented as the output end of the follower circuit and the input end of the frequency compensation circuit.

[0061] The follower circuit is used to make the output voltage follow the input voltage without gain or attenuation, keeping the original amplitude form of the signal. The eleventh resistor R11 is used to current-limiting coupling for the second amplifier U2, and the second capacitor C2 is connected in series with R11 and connected to the positive power supply terminal of the operational amplifier U2, which provides power supply voltage stabilization and provides direct current isolation and filtering for the circuit. The second amplifier U2 is used as a unity gain buffer, and the in-phase input terminal directly receives the signal from the eleventh resistor R11, which is the audio voltage of the first output signal after amplitude modulation in the previous stage; the anti-phase input terminal is short-circuited with the output terminal, forming a direct negative feedback loop, and the negative feedback will automatically adjust the output to make the voltage difference at the input terminal tend to zero, that is, the output voltage can be approximately equal to the input voltage. The positive power supply terminal of the second amplifier U2 is connected in series with the second capacitor C2 and the eleventh resistor R11, and the negative power supply terminal is grounded. The second capacitor C2 can filter out power supply noise and ensure stable power supply during signal processing.

[0062] Further, the frequency compensation circuit includes a thirteenth resistor R13, a fourteenth resistor R14, a fifteenth resistor R15, a sixteenth resistor R16, a third capacitor C3, a first inductor L1 and a third amplifier U3.

[0063] One end of the sixteenth resistor R16 and one end of the thirteenth resistor R13, and the anti-phase input terminal of the third amplifier U3 are all connected to the endpoint E1, and the other end of the thirteenth resistor R13 is grounded. The in-phase input terminal of the third amplifier U3 is connected with a reference voltage Vref; the other end of the sixteenth resistor R16 and one end of the fourteenth resistor R14, and one end of the first inductor L1 are connected to the same point, and the point is provided with a first positive voltage VCC1; the other end of the fourteenth resistor R14 is connected in series with the third capacitor C3 and the ground terminal; the other end of the first inductor L1 is connected to one end of the fifteenth resistor R15, and the other end of the fifteenth resistor R15 and the output terminal of the third amplifier U3 are connected to the same point and set as the endpoint E2, which is represented as the output terminal of the frequency compensation circuit and the input terminal of the comparator unit.

[0064] The thirteenth resistor R13 is used as a voltage division load, the sixteenth resistor R16 and the fourteenth resistor R14 and the first inductor L1 constitute a frequency response network, the sixteenth resistor R16 helps to stabilize the overall gain and frequency response of the circuit by adjusting the signal current; the fourteenth resistor R14 is connected in series with the third capacitor C3 and then grounded, constituting a high-frequency attenuation path, forming an impedance reduction path for high-frequency noise, so that the high-frequency signal is effectively attenuated, reducing the interference transmitted to the subsequent operational amplifier. The first positive voltage VCC1 is used to provide a DC bias potential to the circuit part of the sixteenth resistor R16 and the first inductor L1, ensuring that the subsequent third amplifier U3 performs linear amplification within the appropriate voltage level range. The impedance of the first inductor L1 increases with the increase of frequency, and the impedance is small for low-frequency signals and large for high-frequency signals. The first inductor L1 and the fifteenth resistor R15 constitute a frequency-dependent feedback network, which can adjust the feedback ratio of the third amplifier U3 and adjust the phase and amplitude of the signal. The third amplifier U3 is used for active filtering and frequency compensation, cooperating with the filtering and frequency response network, which can significantly reduce the high-frequency interference in the audio signal, prevent false triggering of the amplitude limiting control, and at the same time ensure the stability of the signal received by the comparator unit in amplitude, frequency and waveform. The reference voltage Vref connected to the non-inverting input end is used to prevent the signal from drifting to the nonlinear region or exceeding the linear output range of the operational amplifier when biased improperly, and to provide a stable reference level for the third amplifier U3, so that the output has a clear voltage reference point; the operational amplifier makes the level of the reference voltage Vref at the non-inverting input end close to that of the first output signal after pre-processing at the inverting input end, so as to drive the output end to transmit the first output signal to the comparator unit.

[0065] Further, as a feasible implementation manner, the comparator unit comprises a twelfth resistor R12, a third comparator Y3 and a fourth capacitor C4; the non-inverting input end of the third comparator Y3 is connected to the endpoint E2, the inverting input end of the third comparator Y3 is connected to one end of the twelfth resistor R12, and the other end of the twelfth resistor R12 is set as the second discrimination input end CIN; the negative power supply end of the third comparator Y3 is grounded, and the positive power supply end of the third comparator Y3 and one end of the fourth capacitor C4 are connected to the same point, and the second positive voltage VCC2 is set at the point, and the other end of the fourth capacitor C4 is grounded; the output end of the third comparator Y3 is set as the discrimination output end BOUT.

[0066] The output result of the discrimination output terminal BOUT of the comparator unit is high level and low level, and in the embodiment, the high level is set as the effective level. That is, the high level signal is the start signal, which can drive the audio attenuation module to input the audio input signal to the audio linear attenuation circuit; the low level signal represents the invalid signal, so that the audio attenuation module does not perform the limiting amplitude processing and the secondary voltage evaluation on the audio input signal, and directly generates the signal as the first output signal. The signal input by the second discrimination input terminal CIN is the combined voltage signal, the twelfth resistor R12 is used to introduce the combined voltage signal as the reference signal and provide the basic load. The fourth capacitor C4 is used for power decoupling, stabilizing the power input, and suppressing the power noise. The second positive voltage VCC2 is used to provide the positive voltage for the operation of the comparator. The third comparator Y3 is used to perform the signal voltage comparison operation, and compares the first output signal after the pre-processing with the combined voltage signal. When the voltage value of the first output signal is higher than that of the combined voltage signal, the third comparator Y3 outputs the high level; when the voltage value of the first output signal is lower than that of the combined voltage signal, the third comparator Y3 outputs the low level.

[0067] The above detailed description further explains the purpose, technical scheme and beneficial effects of the present application. It should be understood that the above description is only a specific embodiment of the present application, and is not used to limit the protection scope of the present application. Any modification, equivalent replacement, improvement, etc. within the spirit and principle of the present application should be included in the protection scope of the present application.

Claims

1. A final stage voltage tracking clipper circuit for an audio power amplifier, characterized by, The circuit comprises: a voltage dividing circuit for receiving a first final-stage voltage and a second final-stage voltage from a target power amplifier device, inputting the first final-stage voltage and the second final-stage voltage to an audio attenuation module, and inputting the first final-stage voltage and the second final-stage voltage to a start-up discrimination module in the form of a combined voltage signal; the audio attenuation module for receiving an audio input signal from the target power amplifier device, the first final-stage voltage and the second final-stage voltage, and a start-up signal from the start-up discrimination module, when the start-up signal is received and the amplitude of the audio input signal exceeds the first final-stage voltage and the second final-stage voltage, performing amplitude modulation on the audio input signal to generate a first output signal representing the output of the power amplifier, and when the start-up signal is not received, outputting the audio input signal as a second output signal; the start-up discrimination module for receiving the combined voltage signal and the first output signal, comparing the combined voltage signal as a reference voltage threshold with the first output signal, when the voltage of the first output signal is higher than the reference voltage threshold, outputting a start-up signal to start the amplitude modulation of the audio attenuation module, and when the voltage of the first output signal is lower than the reference voltage threshold, not outputting the start-up signal; wherein the first final-stage voltage represents a positive final-stage power supply voltage of the target power amplifier device, and the second final-stage voltage represents a negative final-stage power supply voltage of the target power amplifier device; the first output signal is input to a first discrimination input end of the start-up discrimination module, and the combined voltage signal generated by the voltage dividing circuit is input to a second discrimination input end of the start-up discrimination module, and a discrimination output end of the start-up discrimination module is connected to an enable end of the audio attenuation module.

2. The voltage tracking clipping circuit for the last stage of an audio power amplifier according to claim 1, wherein, The audio attenuation module comprises an audio linear attenuation circuit and a running module with an enable end, the audio linear attenuation circuit receives the audio input signal, the first final-stage voltage and the second final-stage voltage, the running module receives the start-up signal, and the audio linear attenuation circuit and the running module are signal-connected; an input end of the audio linear attenuation circuit is set as an attenuation input end for receiving the audio input signal, and an output end of the audio linear attenuation circuit is set as an attenuation output end for generating the first output signal. The audio linear attenuation circuit comprises: a sampling branch for collecting the first final-stage voltage and the second final-stage voltage received from the target power amplifier device, constituting a positive-negative symmetrical power supply voltage, and serving as a reference voltage for amplitude modulation of the audio input signal; a main control circuit for receiving the audio input signal, obtaining the reference values of the first final-stage voltage and the second final-stage voltage received by the sampling branch, and comparing the reference values with the audio input signal, when the audio input signal is higher than the reference values, adjusting the voltage values of the charge and discharge in the conduction loop, so that the voltage value of the audio input signal is amplitude-modulated, and then generating the first output signal, and when the audio input signal is lower than the reference values, outputting the audio input signal as the second output signal.

3. The voltage tracking clipping circuit for the last stage of an audio power amplifier according to claim 2, wherein The main control circuit comprises a first amplifier U1, a first field effect transistor Q1, a first resistor R1, a second resistor R2, a third resistor R3, a fifth resistor R5, a sixth resistor R6, a first capacitor C1, a first comparator Y1 and a second comparator Y2, wherein the first field effect transistor Q1 is an N-channel field effect transistor; One end of the first resistor R1 is set as an attenuation input end AIN, and the other end is connected to a same point with one end of the second resistor R2 and one end of the fourth resistor R4; the other end of the second resistor R2 is connected to a same point with one end of the third resistor R3 and a non-inverting input end of the first amplifier U1; the other end of the fourth resistor R4 is connected to a S pole of the first field effect transistor Q1; a D pole of the first field effect transistor Q1 is grounded, and a G pole is connected to a same point with one end of the first capacitor C1, one end of the fifth resistor R5 and one end of the sixth resistor R6; the other end of the sixth resistor R6 is connected to a same point with the other end of the first capacitor C1, and a negative voltage VEE is set at the point; the other end of the fifth resistor R5 is connected to a same point with an output end of the first comparator Y1 and an output end of the second comparator Y2 through an inverter; an inverting input end of the first comparator Y1, a non-inverting input end of the second comparator Y2, the other end of the third resistor R3 and an output end of the first amplifier U1 are connected to a same point and set as an attenuation output end AOUT; the non-inverting input end of the first comparator Y1 and the inverting input end of the second comparator Y2 are respectively connected to a sampling branch.

4. The voltage tracking clipping circuit for the last stage of an audio power amplifier according to claim 3, wherein, The sampling branch of the first comparator Y1 comprises a seventh resistor R7 and an eighth resistor R8; one end of the seventh resistor R7 is connected to a first final stage voltage VP, the other end of the seventh resistor R7 is connected to a same point with one end of the eighth resistor R8 and the non-inverting input end of the first comparator Y1, and the other end of the eighth resistor R8 is grounded.

5. The voltage tracking clipping circuit for the last stage of an audio power amplifier according to claim 3, wherein, The sampling branch of the second comparator Y2 comprises a ninth resistor R9 and a tenth resistor R10; one end of the ninth resistor R9 is connected to a second final stage voltage VN, the other end of the ninth resistor R9 is connected to a same point with one end of the tenth resistor R10 and the non-inverting input end of the second comparator Y2, and the other end of the tenth resistor R10 is grounded.

6. The voltage tracking clipper circuit for the last stage of an audio power amplifier according to claim 1, wherein, The start judgment module comprises a follower circuit, a frequency compensation circuit and a comparator unit, the first output signal is input to the follower circuit, and the combined voltage signal is input to the comparator unit; The follower circuit is used for amplifying a weak signal and keeping voltage following, and using low output impedance to eliminate distortion amplitude of the first output signal; the frequency compensation circuit is used for suppressing high-frequency noise and keeping signal strength of the first output signal transmitted by the follower circuit; the comparator unit is used for receiving the combined voltage signal, performing voltage comparison between the combined voltage signal as a reference voltage threshold and the first output signal, and setting an output end of the comparator unit as an output end of the start judgment module for outputting a start signal.

7. The voltage tracking clipper circuit for the last stage of an audio power amplifier according to claim 6, wherein, The follower circuit comprises an eleventh resistor R11, a second capacitor C2 and a second amplifier U2, one end of the eleventh resistor R11 is connected to the same point with the non-inverting input terminal of the second amplifier U2, and the point is set as the first discrimination input terminal BIN; the other end of the eleventh resistor R11 is connected in series with the second capacitor C2 and the power supply positive terminal of the second amplifier U2 in sequence, and the power supply negative terminal of the second amplifier U2 is grounded; the inverting input terminal of the second amplifier U2 is connected to the same point with the output terminal of the second amplifier U2, and the point is set as the end point E1, which is represented as the output terminal of the follower circuit and the input terminal of the frequency compensation circuit.

8. The voltage tracking clipper circuit for the last stage of an audio power amplifier according to claim 7, wherein, The frequency compensation circuit comprises a thirteenth resistor R13, a fourteenth resistor R14, a fifteenth resistor R15, a sixteenth resistor R16, a third capacitor C3, a first inductor L1 and a third amplifier U3; One end of the sixteenth resistor R16 and one end of the thirteenth resistor R13, and the inverting input terminal of the third amplifier U3 are all connected to the end point E1, and the other end of the thirteenth resistor R13 is grounded, and the non-inverting input terminal of the third amplifier U3 is connected with a reference voltage Vref; the other end of the sixteenth resistor R16 and one end of the fourteenth resistor R14 and one end of the first inductor L1 are connected to the same point, and the point is provided with a first positive voltage VCC1; the other end of the fourteenth resistor R14 is connected in series with the third capacitor C3 and the ground terminal in sequence; the other end of the first inductor L1 is connected to one end of the fifteenth resistor R15, and the other end of the fifteenth resistor R15 is connected to the same point with the output terminal of the third amplifier U3, and the point is set as the end point E2, which is represented as the output terminal of the frequency compensation circuit and the input terminal of the comparator unit.

9. The voltage tracking clipper circuit for the last stage of an audio power amplifier according to claim 8, wherein, The comparator unit comprises a twelfth resistor R12, a third comparator Y3 and a fourth capacitor C4; the non-inverting input terminal of the third comparator Y3 is connected to the end point E2, the inverting input terminal of the third comparator Y3 is connected to one end of the twelfth resistor R12, and the other end of the twelfth resistor R12 is set as the second discrimination input terminal CIN; the power supply negative terminal of the third comparator Y3 is grounded, and the power supply positive terminal of the third comparator Y3 is connected to the same point with one end of the fourth capacitor C4, and the point is provided with a second positive voltage VCC2, and the other end of the fourth capacitor C4 is grounded; the output terminal of the third comparator Y3 is set as the discrimination output terminal BOUT.

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