Audio amplifier

Abstract

The invention relates to an audio amplifier which comprises a filter circuit, a feedback circuit, a differential amplification circuit and a post-stage signal processing circuit, the differential amplification circuit comprises four input ends and two output ends, the filter circuit is connected with two of the four input ends of the differential amplification circuit, and the feedback circuit is connected with the two output ends of the differential amplification circuit. The filter circuit is also connected with a first input signal and a second input signal, the feedback circuit is connected with the other two of the two output ends and the four input ends of the differential amplification circuit, and the two output ends of the differential amplification circuit are connected with the post-stage signal processing circuit. The audio amplifier disclosed by the invention can meet the requirements of low-frequency sound source processing, low noise, insensitivity to mismatch of circuit elements and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of signal amplifiers, and more particularly to an audio amplifier. Background Art

[0002] With the rapid advancement of CMOS (complementary metal oxide semiconductor) manufacturing technology, device feature sizes continue to shrink, while power supply voltages also continue to decrease, resulting in noise limitations on analog circuit performance. Fixed-gain amplifiers typically consist of a high-gain amplifier circuit and a feedback network, typically implemented with a voltage-divider resistor. The amplifier's total noise is composed of the amplifier circuit noise and the voltage-divider resistor noise. The amplifier circuit noise is determined by the amplifier circuit structure, transistor parameter values, and bias conditions. A lower noise level can be achieved by properly setting these parameters. To reduce the amplifier's total noise, the voltage-divider resistor noise also needs to be optimized. Resistor noise is proportional to the resistor value, so reducing the voltage-divider resistor value can reduce noise. However, to achieve better noise immunity and flexible common-mode voltage settings, a fully differential amplifier structure is generally used, with capacitive coupling between stages. The desired gain is achieved by adjusting the resistor ratio. This structure exhibits a high-pass input stage, with a cutoff frequency determined by the capacitor and resistor. Reducing the resistor value increases the cutoff frequency, making the amplifier unable to process some low-frequency signals. For example, audio amplifiers require a minimum signal frequency of 20Hz, so reducing the resistor value to reduce noise reaches a bottleneck.

[0003] Another amplifier in the prior art includes two operational amplifier circuits. The input signal is applied to the non-inverting input terminals of the two operational amplifier circuits, and the corresponding output signal is generated according to the proportional relationship of the resistors. The desired amplification factor is achieved by adjusting the resistor ratio. Because the impedance of the operational amplifier circuit input terminal is very high, even if the input signal is coupled through capacitance, there is no problem of low-frequency signal attenuation. Therefore, the resistance value can be flexibly adjusted to achieve the desired noise performance. However, this structure requires the two resistors to be equal to achieve ideal signal amplification. If the offset of the two operational amplifier circuits is mismatched or the resistors are mismatched, the output signal will produce a common-mode component, thereby reducing the circuit's common-mode rejection ratio and power supply rejection ratio.

[0004] Therefore, it is difficult for existing technologies to meet the requirements of low-frequency sound source processing, low noise and insensitivity to resistance mismatch. Summary of the Invention

[0005] The object of the present invention is to provide an audio amplifier that can meet the requirements of low-frequency sound source processing, low noise and insensitivity to resistance mismatch.

[0006] Based on the above objectives, the present invention provides an audio amplifier, comprising a filter circuit, a feedback circuit, a differential differential amplifier circuit, and a post-stage signal processing circuit. The differential differential amplifier circuit comprises four input terminals and two output terminals. The filter circuit is connected to two of the four input terminals of the differential differential amplifier circuit. The filter circuit is also connected to a first input signal and a second input signal. The feedback circuit is connected to the two output terminals of the differential differential amplifier circuit and the other two of the four input terminals. The two output terminals of the differential differential amplifier circuit are connected to the post-stage signal processing circuit.

[0007] Furthermore, the four input terminals of the differential differential amplifier circuit include a first non-inverting input terminal, a first inverting input terminal, a second non-inverting input terminal, and a second inverting input terminal; the two output terminals of the differential differential amplifier circuit include a non-inverting output terminal and an inverting output terminal; the filtering circuit includes a first capacitor and a second capacitor; and the feedback circuit includes an adjustable resistor, a first resistor, and a second resistor;

[0008] The first end of the first capacitor is connected to the first input signal, the second end of the first capacitor is connected to the first non-inverting input terminal, the first end of the second capacitor is connected to the second input signal, the second end of the second capacitor is connected to the second non-inverting input terminal, the first end of the adjustable resistor is connected to the first inverting input terminal and the first end of the first resistor, the second end of the adjustable resistor is connected to the second inverting input terminal and the first end of the second resistor, the non-inverting output terminal is connected to the second end of the first resistor and the first input terminal of the post-stage signal processing circuit, and the inverting output terminal is connected to the second end of the second resistor and the second input terminal of the post-stage signal processing circuit.

[0009] Furthermore, it also includes a third resistor and a fourth resistor, the first end of the third resistor is connected to the first in-phase input terminal, the first end of the fourth resistor is connected to the second in-phase output terminal, and the second end of the third resistor and the second end of the fourth resistor are both connected to a preset common-mode voltage.

[0010] Furthermore, the four input terminals of the differential differential amplifier circuit include a first non-inverting input terminal, a first inverting input terminal, a second non-inverting input terminal, and a second inverting input terminal; the two output terminals of the differential differential amplifier circuit include a non-inverting output terminal and an inverting output terminal; the filtering circuit includes a first capacitor and a second capacitor; and the feedback circuit includes an adjustable resistor, a first resistor, and a second resistor;

[0011] The first end of the first capacitor is connected to the first input signal, the second end of the first capacitor is connected to the first non-inverting input terminal, the first end of the second capacitor is connected to the second input signal, the second end of the second capacitor is connected to the first inverting input terminal, the first end of the adjustable resistor is connected to the second non-inverting input terminal and the first end of the first resistor, the second end of the adjustable resistor is connected to the second inverting input terminal and the first end of the second resistor, the non-inverting output terminal is connected to the second end of the first resistor and the first input terminal of the post-stage signal processing circuit, and the inverting output terminal is connected to the second end of the second resistor and the second input terminal of the post-stage signal processing circuit.

[0012] Furthermore, it also includes a third resistor and a fourth resistor, the first end of the third resistor is connected to the first in-phase input terminal, the first end of the fourth resistor is connected to the second in-phase output terminal, and the second end of the third resistor and the second end of the fourth resistor are both connected to a preset common-mode voltage.

[0013] Furthermore, the differential amplifier circuit is an active amplifier composed of CMOS transistors.

[0014] Furthermore, the third resistor and the fourth resistor are arranged inside the differential amplifier circuit.

[0015] Furthermore, the third resistor and the fourth resistor are used to set the common mode voltage of the first non-inverting input terminal and the second non-inverting input terminal of the differential differential amplifier circuit.

[0016] Furthermore, the post-stage signal processing circuit is used to filter and / or amplify the signal and / or power amplify the output signal of the differential amplifier circuit. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is a schematic diagram of the circuit structure of an existing audio amplifier;

[0018] Figure 2 A schematic diagram of the circuit structure of another existing audio amplifier;

[0019] Figure 3 is a schematic diagram of the circuit structure of an audio amplifier according to a first embodiment of the present invention;

[0020] Figure 4 is a circuit diagram of an audio amplifier according to a second embodiment of the present invention;

[0021] Figure 5 is a schematic diagram of the circuit structure of an audio amplifier according to a third embodiment of the present invention;

[0022] Figure 6 Schematic diagram of the circuit structure of an audio amplifier according to the fourth embodiment of the present invention. Detailed implementation

[0023] The following will give and describe in detail the preferred embodiments of the present invention in conjunction with the accompanying drawings.

[0024] As Figure 1 shown, an audio amplifier in the prior art includes a capacitor 101, a capacitor 102, a resistor 103, a resistor 104, a variable resistor 105, a variable resistor 106, a fully differential operational amplifier circuit 107, and a post-stage signal processing circuit 108. One end of the capacitor 101 is connected to the first input signal V IN1 , the other end of the capacitor 101 is connected to one end of the resistor 103, the other end of the resistor 103 is respectively connected to one end of the variable resistor 105 and the non-inverting input terminal of the fully differential operational amplifier circuit 107. The inverting output terminal of the fully differential operational amplifier circuit 107 is respectively connected to the other end of the variable resistor 105 and the first input terminal of the post-stage signal processing circuit 108. One end of the capacitor 102 is connected to the second input signal V IN2 , the other end of the capacitor 102 is connected to one end of the resistor 104, the other end of the resistor 104 is respectively connected to one end of the variable resistor 106 and the inverting input terminal of the fully differential operational amplifier circuit 107. The non-inverting output terminal of the fully differential operational amplifier circuit 107 is respectively connected to the other end of the variable resistor 106 and the second input terminal of the post-stage signal processing circuit 108; the variable resistor 105 and the variable resistor 106 are respectively arranged in parallel with the fully differential operational amplifier circuit and form a feedback circuit. The feedback circuit is used to feedback the output signal of the fully differential operational amplifier 107 to the input terminal; the inverting output terminal of the fully differential operational amplifier circuit 107 outputs the second output signal V OUT2 , the non-inverting output terminal outputs the first output signal V OUT1 . The fully differential operational amplifier circuit 107 can detect and amplify the difference between the two input signals. The output signal is embodied as the differential-mode signal of the non-inverting output terminal and the inverting output terminal. The common-mode levels of the non-inverting output terminal and the inverting output terminal are kept constant through the internal common-mode feedback module; the second output signal V OUT2 is input to the first input terminal of the post-stage signal processing circuit 108, the first output signal V OUT1 is input to the second input terminal of the post-stage signal processing circuit 108. The post-stage signal processing circuit 108 is used to process the first output signal V OUT1 and the second output signal V OUT2 , including but not limited to filtering, signal amplification, power amplification, etc.

[0025] Capacitor 101, capacitor 102, resistor 103 and resistor 104 form a filter circuit, which is used to isolate the DC level of the input source from the DC level of the two input terminals of the fully differential operational amplifier circuit 107. The filter circuit has a high-pass characteristic, and its cut-off frequency f -3db It can be calculated using the following formula:

[0026]

[0027] Among them, C in is the capacitance value of capacitor 101 and capacitor 102 (the capacitance values of capacitor 101 and capacitor 102 are equal), R in is the resistance value of the resistor 103 and the resistor 104 (the resistance values of the resistor 103 and the resistor 104 are equal).

[0028] Audio amplifier output noise V noise_out It can be calculated using the following formula:

[0029]

[0030] Among them, R fb is the resistance value of the adjustable resistor 105 and the adjustable resistor 106 (the resistance values of the two adjustable resistors are equal), R in is the resistance value of resistor 103 and resistor 104, V noise_opa is the noise value of the fully differential operational amplifier circuit 107, k is the Boltzmann constant, and T is the operating temperature of the audio amplifier.

[0031] The noise value of the fully differential operational amplifier circuit 107 is determined by the amplifier circuit structure, transistor parameter values and bias conditions. A smaller noise level can be obtained by setting appropriate parameters. In other words, the noise value of the audio amplifier is mainly determined by the resistor noise, where R fb and R in The ratio of R determines the gain of the audio amplifier and is usually a fixed value. in The smaller the resistance value, the smaller the thermal noise of the resistor, so the noise of the audio amplifier is smaller. In practical applications, the capacitance values of capacitors 101 and 102 will not be very large, reducing R in A higher resistance value will increase the cutoff frequency of the filter circuit, thereby attenuating low-frequency sound sources.

[0032] like Figure 2 As shown, another existing audio amplifier includes a capacitor 201, a capacitor 202, an adjustable resistor 203, a resistor 204, a resistor 205, an operational amplifier circuit 206, an operational amplifier circuit 207 and a post-stage signal processing circuit 208. The first end of the capacitor 201 is connected to the first input signal V IN1is connected, the second terminal of the capacitor 201 is connected to the non-inverting input terminal of the operational amplifier circuit 206, and the first terminal of the second capacitor 202 is connected to the non-inverting input terminal of the operational amplifier circuit 207. The output terminal of the operational amplifier circuit 206 is respectively connected to the first terminal of the resistor 204 and the first input terminal of the subsequent signal processing circuit 208. The inverting input terminal of the operational amplifier circuit 206, the second terminal of the resistor 204, and the first terminal of the adjustable resistor 203 are interconnected. The second terminal of the adjustable resistor 203, the inverting input terminal of the operational amplifier circuit 207, and the first terminal of the resistor 205 are interconnected. The output terminal of the operational amplifier circuit 207 is respectively connected to the second terminal of the resistor 205 and the second input terminal of the subsequent signal processing circuit 208. The operational amplifier circuit 206 outputs a second output signal V IN2 is connected, the second terminal of the second capacitor 202 is connected to the non-inverting input terminal of the operational amplifier circuit 207. The output terminal of the operational amplifier circuit 206 is respectively connected to the first terminal of the resistor 204 and the first input terminal of the subsequent signal processing circuit 208. The inverting input terminal of the operational amplifier circuit 206, the second terminal of the resistor 204, and the first terminal of the adjustable resistor 203 are interconnected. The second terminal of the adjustable resistor 203, the inverting input terminal of the operational amplifier circuit 207, and the first terminal of the resistor 205 are interconnected. The output terminal of the operational amplifier circuit 207 is respectively connected to the second terminal of the resistor 205 and the second input terminal of the subsequent signal processing circuit 208. The operational amplifier circuit 206 outputs a second output signal V OUT2 to the first input terminal of the subsequent signal processing circuit 208, and the operational amplifier circuit 207 outputs a first output signal V OUT1 to the second input terminal of the subsequent signal processing circuit 208.

[0033] The capacitor 201 and the capacitor 202 form a filter circuit, which exhibits a high-pass characteristic, and the cut-off frequency f -3db can be calculated by the following formula:

[0034]

[0035] where C in is the capacitance value of the capacitor 201 and the capacitor 202, and R in_opa is the input impedance of the non-inverting input terminals of the operational amplifier circuit 206 and the operational amplifier circuit 207, which is a very large value. Therefore, even if the capacitance values of the capacitor 201 and the capacitor 202 are taken to be small, the cut-off frequency of the filter can be made very low, so that low-frequency sound sources can be transmitted without attenuation.

[0036] The adjustable resistor 203, the resistor 204, and the resistor 205 form a feedback circuit, which is used to feedback the output signals of the operational amplifier 206 and the operational amplifier 207 to the output terminal. Both the operational amplifier circuit 206 and the operational amplifier circuit 207 can detect and amplify the difference of the input signals, and the output result is reflected as the voltage magnitude at the output terminal. The subsequent signal processing circuit 208 is used to process the first output signal V OUT1 and the second output signal V OUT2 , including but not limited to filtering processing, signal amplification processing, power amplification processing, etc.

[0037] In Figure 2In the audio amplifier, the low-frequency sound source is allowed to be transmitted without attenuation while reducing the noise of the audio amplifier. However, the offset mismatch between the operational amplifier circuit 206 and the operational amplifier circuit 207 and the mismatch between the resistor 204 and the resistor 205 will deteriorate the common-mode rejection ratio and power supply rejection ratio of the audio amplifier.

[0038] Therefore, although the existing technology can solve the contradiction between low-frequency sound source transmission and audio amplifier noise reduction by introducing two operational amplifier circuits, the offset mismatch of the two operational amplifier circuits and the resistor mismatch will deteriorate the common-mode rejection ratio and power supply rejection ratio of the audio amplifier. To solve this problem, an embodiment of the present invention provides a low-noise audio amplifier that is insensitive to resistor mismatch.

[0039] First embodiment

[0040] like Figure 3 As shown, the first embodiment of the present invention provides an audio amplifier, which includes a filter circuit, a feedback circuit, a differential amplifier circuit 306, and a post-stage signal processing circuit 307. The differential amplifier circuit 306 includes four input terminals and two output terminals. The four input terminals include a first non-inverting input terminal, a first inverting input terminal, a second non-inverting input terminal, and a second inverting input terminal. The two output terminals include a non-inverting output terminal and an inverting output terminal. The filter circuit is connected to an input source and two of the input terminals of the differential amplifier circuit 306. The input source is used to convert the first input signal V IN1 and the second input signal V IN2 An input filter circuit is used to isolate the DC level of the input source from the DC levels of the two input terminals of the differential differential amplifier circuit 306, so as to transmit the input signal within the target bandwidth. A feedback circuit is arranged in parallel with the differential differential amplifier circuit 306, and is used to feed back the output signal of the differential differential amplifier circuit 306 to the input terminal. The differential differential amplifier circuit 306 is connected to the post-stage signal processing circuit 307. The differential differential amplifier circuit 306 is used to detect and amplify the difference between the two sets of input signals. The output result is reflected in the differential-mode signal of the two output terminals. The differential-mode signals of the two output terminals have opposite phases, and the common-mode level of the two output terminals is kept constant by the internal common-mode feedback module.

[0041] The filter circuit includes a first capacitor 301 and a second capacitor 302. The feedback circuit includes an adjustable resistor 303, a first resistor 304, and a second resistor 305. The first end of the first capacitor 301 is connected to the first input signal V IN1 The second end of the first capacitor 301 is connected to the first non-inverting input terminal of the differential amplifier circuit 306, and the first end of the second capacitor 302 is connected to the second input signal V IN2The first end of the adjustable resistor 303 is connected to the first inverting input terminal of the differential differential amplifier circuit 306 and the first end of the first resistor 304. The second end of the adjustable resistor 303 is connected to the second inverting input terminal of the differential differential amplifier circuit 306 and the first end of the second resistor 305. The non-inverting output terminal of the differential differential amplifier circuit 306 is connected to the second end of the first resistor 304 and the first input terminal of the post-stage signal processing circuit 307, and the first output signal VOUT1 is output to the first input terminal of the post-stage signal processing circuit 307. The inverting output terminal of the differential differential amplifier circuit 306 is connected to the second end of the second resistor 305 and the second input terminal of the post-stage signal processing circuit 307, and the second output signal VOUT2 is output to the second input terminal of the post-stage signal processing circuit 307.

[0042] The filter circuit presents high-pass characteristics, and its cut-off frequency can also be expressed by formula (3), where C in is the capacitance value of the first capacitor 301 and the second capacitor 302, R in_opa It is the input impedance of the first non-inverting input terminal and the second non-inverting input terminal of the differential differential amplifier circuit 306. This is a large value. Therefore, even if the capacitance values of the first capacitor 301 and the second capacitor 302 are small, the cutoff frequency of the filter circuit can be made very low, thereby being able to transmit low-frequency sound sources without attenuation.

[0043] The differential amplifier circuit 107 may be an active amplifier composed of CMOS transistors.

[0044] The differential amplifier circuit 306 can detect and amplify the first input signal V IN1 and the second input signal V IN2 The output signal is reflected as the differential mode signal of the in-phase output terminal and the inverting output terminal. The common mode level of the in-phase output terminal and the inverting output terminal is kept constant by the internal common mode feedback module. The specific operation relationship can be calculated by the following formula:

[0045] V OUT1 -V OUT2 =A((V P1 -V N1 )-(V P2 -V N2 )) (4)

[0046] Among them, V P1 is the signal of the first non-inverting input terminal of the differential amplifier circuit 306, V N1 is the signal of the first inverting input terminal of the differential amplifier circuit 306, V P2 is the signal of the second non-inverting input terminal of the differential amplifier circuit 306, VN2 is the signal of the second inverting input terminal of the differential amplifier circuit 306 , and A is the amplification factor of the differential amplifier circuit 306 , which is a large value.

[0047] The post-stage signal processing circuit 307 is used to process the first output signal V of the differential amplifier circuit 306. OUT1 and the second output signal V OUT2 , including but not limited to filtering processing, signal amplification processing, power amplification processing and other functions.

[0048] In this embodiment, the input impedance of the differential amplifier circuit 306 is very high, which can isolate the filter circuit and the feedback circuit, thereby allowing the low-frequency sound source to be transmitted without attenuation while reducing the noise of the audio amplifier. Figure 2 The two operational amplifier circuits are combined, and the differential differential amplifier circuit 306 can be implemented more compactly on the layout, thereby alleviating the mismatch of the two sets of input stage offsets. Finally, the differential differential amplifier circuit 306 also uses a common-mode feedback module to ensure that the common-mode voltage at the in-phase output terminal and the inverting output terminal is constant. Even if the first resistor 304 and the second resistor 305 are offset, the output signal of the amplifier circuit will not generate a common-mode component, thereby reducing the impact of the mismatch of the feedback circuit components on the audio amplifier and improving the common-mode rejection ratio and power supply rejection ratio of the audio amplifier.

[0049] The audio amplifier of the first embodiment of the present invention can meet the requirements of low-frequency sound source processing, low noise, and insensitivity to circuit element mismatch.

[0050] Second embodiment

[0051] like Figure 4 As shown, the second embodiment of the present invention provides an audio amplifier, which, based on the first embodiment, further includes a third resistor 408 and a fourth resistor 409. The first end of the third resistor 408 is connected to the first non-inverting input terminal of the differential amplifier circuit 306, the first end of the fourth resistor 409 is connected to the second non-inverting input terminal of the differential amplifier circuit 306, and the second end of the third resistor 408 and the second end of the fourth resistor 409 are both connected to the preset common mode voltage V CM connected.

[0052] The third resistor 408 and the fourth resistor 409 are used to set the common-mode voltage of the first non-inverting input terminal and the second non-inverting input terminal of the differential difference amplifier circuit 306. At the same time, the cut-off frequency of the filter circuit will also be changed. However, the resistance values of the third resistor 408 and the fourth resistor 409 can be set to a relatively large value to obtain a low cut-off frequency. The total integrated noise generated by the third resistor 408 and the fourth resistor 409 is determined by the capacitance values of the first capacitor 301 and the second capacitor 302. By setting reasonable capacitance values of the first capacitor 301 and the second capacitor 302, the noise generated by the third resistor 408 and the fourth resistor 409 can be ignored.

[0053] The third resistor 408 and the fourth resistor 409 can also be provided inside the differential difference amplifier circuit 306.

[0054] Therefore, the audio amplifier according to the second embodiment of the present invention can also meet the requirements such as low-frequency sound source processing, low noise, and insensitivity to circuit element mismatch.

[0055] Third Embodiment

[0056] As Figure 5 shown, the third embodiment of the present invention provides an audio amplifier, which has basically the same circuit structure as the audio amplifier of the first embodiment, except that the connection manner of the filter circuit and the feedback circuit is modified. Specifically, in the audio amplifier of the third embodiment, the first end of the first capacitor 301 is still connected to the first input signal V IN1 , the second end of the first capacitor 301 is connected to the first non-inverting input terminal of the differential difference amplifier circuit 306, the first end of the second capacitor 302 is still connected to the second input signal V IN2 , the second end of the second capacitor 302 is connected to the first inverting input terminal of the differential difference amplifier circuit 306, the first end of the adjustable resistor 303 is connected to the first end of the first resistor 304 and the second non-inverting input terminal of the differential difference amplifier circuit 306, and the second end of the adjustable resistor 303 is connected to the first end of the second resistor 305 and the second inverting input terminal of the differential difference amplifier circuit 306; the connection manner among the second end of the first resistor 304, the second end of the second resistor 305, the four-input differential operational amplifier circuit 306, and the post-stage signal processing circuit 307 is the same as that of the first embodiment, and will not be described herein again.

[0057] The specific operational relationship of the differential difference amplifier circuit is shown in Formula (4). The audio amplifier of the third embodiment can also achieve the same amplification effect as that of the first embodiment.

[0058] The audio amplifier of the third embodiment of the present invention can meet the requirements such as low-frequency sound source processing, low noise, and insensitivity to circuit element mismatch.

[0059] Fourth Embodiment

[0060] As Figure 6 shown, the fourth embodiment of the present invention provides an audio amplifier, which, on the basis of the third embodiment, further includes a third resistor 408 and a fourth resistor 409. The first end of the third resistor 408 is connected to the first non-inverting input terminal of the differential difference amplification circuit 306, and the first end of the fourth resistor 409 is connected to the second non-inverting input terminal of the differential difference amplification circuit 306. The second ends of the third resistor 408 and the fourth resistor 409 are both connected to a preset common-mode voltage V CM connected.

[0061] The third resistor 408 and the fourth resistor 409 are used to set the common-mode voltage of the first non-inverting input terminal and the second non-inverting input terminal of the differential difference amplification circuit 306, and will also change the cut-off frequency of the filter circuit. However, the resistance values of the third resistor 408 and the fourth resistor 409 can be set to a relatively large value to obtain a low cut-off frequency. The total integration noise generated by the third resistor 408 and the fourth resistor 409 is determined by the capacitance values of the first capacitor 301 and the second capacitor 302. By setting reasonable capacitance values of the first capacitor 301 and the second capacitor 302, the noise generated by the third resistor 408 and the fourth resistor 409 can be ignored.

[0062] Therefore, the audio amplifier of the fourth embodiment of the present invention can also meet the requirements of low-frequency sound source processing, low noise, and insensitivity to circuit element mismatch.

[0063] The above are only the preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various changes can be made to the above embodiments of the present invention. That is, all simple, equivalent changes and modifications made according to the claims and the content of the specification of the present invention application fall within the scope of the claims of the present invention patent. Those not described in detail in the present invention are all conventional technical contents.

Claims

1. An audio amplifier, characterized in that, It includes a filter circuit, a feedback circuit, a differential difference amplification circuit, and a post-stage signal processing circuit. The differential difference amplification circuit includes four input terminals and two output terminals. The filter circuit is connected to two of the four input terminals of the differential difference amplification circuit. The filter circuit is also connected to a first input signal and a second input signal. The feedback circuit is connected to the two output terminals of the differential difference amplification circuit and the other two of the four input terminals. The two output terminals of the differential difference amplification circuit are connected to the post-stage signal processing circuit.

2. The audio amplifier according to claim 1, wherein The four input terminals of the differential difference amplification circuit include a first in-phase input terminal, a first anti-phase input terminal, a second in-phase input terminal, and a second anti-phase input terminal. The two output terminals of the differential difference amplification circuit include an in-phase output terminal and an anti-phase output terminal. The filter circuit includes a first capacitor and a second capacitor. The feedback circuit includes a variable resistor, a first resistor, and a second resistor. The first end of the first capacitor is connected to the first input signal, the second end of the first capacitor is connected to the first in-phase input terminal, the first end of the second capacitor is connected to the second input signal, the second end of the second capacitor is connected to the second in-phase input terminal, the first end of the variable resistor is connected to the first anti-phase input terminal and the first end of the first resistor, the second end of the variable resistor is connected to the second anti-phase input terminal and the first end of the second resistor, the in-phase output terminal is connected to the second end of the first resistor and the first input terminal of the post-stage signal processing circuit, and the anti-phase output terminal is connected to the second end of the second resistor and the second input terminal of the post-stage signal processing circuit.

3. The audio amplifier according to claim 2, characterized in that, It further includes a third resistor and a fourth resistor. The first end of the third resistor is connected to the first in-phase input terminal, the first end of the fourth resistor is connected to the second in-phase output terminal, and the second ends of the third resistor and the fourth resistor are both connected to a preset common-mode voltage.

4. The audio amplifier according to claim 1, characterized in that, The four input terminals of the differential difference amplification circuit include a first in-phase input terminal, a first anti-phase input terminal, a second in-phase input terminal, and a second anti-phase input terminal. The two output terminals of the differential difference amplification circuit include an in-phase output terminal and an anti-phase output terminal. The filter circuit includes a first capacitor and a second capacitor. The feedback circuit includes a variable resistor, a first resistor, and a second resistor. The first end of the first capacitor is connected to the first input signal, the second end of the first capacitor is connected to the first in-phase input terminal, the first end of the second capacitor is connected to the second input signal, the second end of the second capacitor is connected to the first anti-phase input terminal, the first end of the variable resistor is connected to the second in-phase input terminal and the first end of the first resistor, the second end of the variable resistor is connected to the second anti-phase input terminal and the first end of the second resistor, the in-phase output terminal is connected to the second end of the first resistor and the first input terminal of the post-stage signal processing circuit, and the anti-phase output terminal is connected to the second end of the second resistor and the second input terminal of the post-stage signal processing circuit.

5. The audio amplifier according to claim 4, wherein It further includes a third resistor and a fourth resistor. The first end of the third resistor is connected to the first non-inverting input terminal, and the first end of the fourth resistor is connected to the second non-inverting output terminal. The second ends of both the third resistor and the fourth resistor are connected to a preset common-mode voltage.

6. The audio amplifier according to claim 1, wherein The differential difference amplifier circuit is an active amplifier composed of CMOS transistors.

7. The audio amplifier according to claim 3 or 5, characterized in that, The third resistor and the fourth resistor are disposed inside the differential difference amplifier circuit.

8. The audio amplifier according to claim 3 or 5, characterized in that, The third resistor and the fourth resistor are used to set the common-mode voltage of the first non-inverting input terminal and the second non-inverting input terminal of the differential difference amplifier circuit.

9. The audio amplifier according to claim 1, characterized in that, The post-stage signal processing circuit is used to filter and / or amplify the signal and / or perform power amplification on the output signal of the differential difference amplifier circuit.

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