A microphone pre-afe circuit with listen-wake function

Abstract

The application discloses a microphone pre-AFE circuit with a listening wake-up function and belongs to the technical field of microphones. The microphone pre-AFE circuit comprises a microphone equivalent model, the output end of the microphone equivalent model is connected with a high-resistance biasing circuit and a listening wake-up circuit, the output end of the high-resistance biasing circuit is connected with an operational amplifier module, and the output end of the operational amplifier module is connected with a post-stage circuit. The operational amplifier module amplifies or attenuates the microphone signal in proportion through the feedback of a variable capacitor. When the microphone pre-AFE circuit is in a normal working mode, only the operational amplifier module works normally, and the listening wake-up circuit does not work. When the microphone pre-AFE circuit enters a listening standby mode, the operational amplifier module does not work, the microphone pre-AFE circuit maintains the listening wake-up circuit with a power consumption lower than that in the normal working mode, and the operational amplifier module amplifies the microphone signal when the listening wake-up circuit outputs a high FLAG signal. The application can realize lower power consumption and noise.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of microphone, in particular to a microphone pre- AFE circuit with a listening wake-up function. BACKGROUND

[0002] The microphone analog front-end (AFE) circuit is the core module of the microphone signal processing system, which is responsible for the level shift, amplification and filtering of the original analog signal output by the microphone sensor such as MEMS microphone or ECM of electret microphone. With the popularity of Internet of Things (IoT) and smart wearable devices, the performance requirements of microphone as the core sensor for sound signal collection are increasing. High signal-to-noise ratio (SNR), low power consumption, small size and strong anti-interference ability have become key indicators. The existing microphone pre- AFE circuit has low signal-to-noise ratio, high power consumption, large size and weak anti-interference ability. SUMMARY

[0003] The present application aims to overcome the shortcomings of the prior art and provide a microphone pre- AFE circuit with a listening wake-up function. When the microphone is in a listening mode, the main circuit of the AFE stops working to detect the input signal amplitude of the AFE with extremely low power consumption. When the input signal amplitude of the AFE circuit exceeds the set threshold, the AFE circuit will automatically wake up and work normally. This reduces the standby power consumption of the microphone system and increases the standby time of the microphone system.

[0004] The purpose of the present application is achieved by the following technical solution: a microphone pre- AFE circuit with a listening wake-up function, comprising a microphone equivalent model, the output end of the microphone equivalent model is connected to a high resistance biasing circuit and a listening wake-up circuit, the output end of the high resistance biasing circuit is connected to an operational amplifier module, and the output end of the operational amplifier module is connected to a post-stage circuit.

[0005] When the microphone pre- AFE circuit is in a normal working mode, only the operational amplifier module works normally, and the listening wake-up circuit does not work. When the microphone pre- AFE circuit enters a listening standby mode, the operational amplifier module does not work, and the microphone pre- AFE circuit maintains the listening wake-up circuit with lower power consumption than the normal working mode. When the listening wake-up circuit outputs a high FLAG signal, the operational amplifier module is woken up to amplify the microphone signal.

[0006] Preferably, the monitoring wake-up circuit comprises a source follower circuit, an input end of the source follower circuit is connected with the microphone equivalent model, an output end of the source follower circuit is connected with a band-pass filter, an output end of the band-pass filter is connected with a variable gain amplifier, an output end of the variable gain amplifier is connected with a high-pass filter, an output end of the high-pass filter is connected with a comparator, and the comparator is used for outputting a FLAG signal.

[0007] Preferably, the high-resistance bias circuit comprises a diode D1, a diode D2, a triode Q1, a triode Q2 and a MOS tube M3; a positive electrode of the diode D1 is connected with the microphone equivalent model, a drain of the MOS tube M3 and an emitter of the triode Q1, a negative electrode of the diode D1 is connected with a base and a collector of the triode Q1; a source and a gate of the MOS tube M3 are connected with a ground GND; the collector of the triode Q1 is connected with a positive electrode of the diode D2; the positive electrode of the diode D2 is connected with a power supply and an emitter of the triode Q2, and a negative electrode of the diode D2 is connected with the ground GND; a collector of the triode Q2 is connected with a base of the triode Q2 and the ground GND.

[0008] Preferably, the source follower circuit is in a differential structure, a non-inverting input end of the source follower circuit is connected with an output end of the microphone equivalent model, an inverting input end of the source follower circuit is connected with the ground GND, and a differential output end of the source follower circuit is connected with an input end of the band-pass filter.

[0009] Preferably, the band-pass filter is a full differential structure, comprising resistors R6, R7, R8, R9, R10, R11, R12, R13, R14, capacitors C5, C6, C7, C8, C9, an amplifier AMP4 and an amplifier AMP5; the first ends of the resistors R13 and R14 are connected to the differential output end of the source follower circuit, the second end of the resistor R13 is connected to the first end of the capacitor C7 and the first end of the capacitor C7, the second end of the resistor R14 is connected to the first end of the capacitor C8 and the second end of the capacitor C9; the second end of the capacitor C7 is connected to the first end of the resistor R11 and the positive input end of the amplifier AMP4; the second end of the capacitor C8 is connected to the first end of the resistor R11 and the positive input end of the amplifier AMP5; the second end of the resistor R11 is connected to the second end of the resistor R12; the negative input end of the amplifier AMP4 is connected to the first ends of the resistors R10 and R8, and the output end of the amplifier AMP4 is connected to the second end of the resistor R8 and the first end of the capacitor C5; the negative input end of the amplifier AMP5 is connected to the second end of the resistor R10 and the first end of the resistor R9, and the output end of the amplifier AMP5 is connected to the second end of the resistor R9 and the first end of the capacitor C6; the second end of the capacitor C5 is connected to the input end of the variable gain amplifier and the first end of the resistor R6; the second end of the capacitor C6 is connected to the input end of the variable gain amplifier and the first end of the resistor R7; the second end of the resistor R6 is connected to the second end of the resistor R7.

[0010] Preferably, the variable gain amplifier is a full differential structure, comprising an amplifier AMP2, an amplifier AMP3, adjustable resistors R3, R4 and R5; the positive input end of the amplifier AMP2 is connected to the output end of the band-pass filter, the negative input end of the amplifier AMP2 is connected to the first ends of the adjustable resistors R3 and R4, and the output end of the amplifier AMP2 is connected to the second end of the adjustable resistor R3 and the input end of the high-pass filter; the second end of the adjustable resistor R4 is connected to the negative input end of the amplifier AMP3 and the first end of the adjustable resistor R5; the positive input end of the amplifier AMP3 is connected to the output end of the band-pass filter, and the output end of the amplifier AMP3 is connected to the second end of the adjustable resistor R5 and the input end of the high-pass filter.

[0011] Preferably, the high-pass filter is a full differential structure, comprising capacitors C3, C4, resistors R1 and R2; the first end of the capacitor C3 is connected to the output end of the variable gain amplifier, and the second end of the capacitor C3 is connected to the first end of the resistor R1 and the positive input end of the comparator; the first end of the capacitor C4 is connected to the output end of the variable gain amplifier, and the second end of the capacitor C4 is connected to the first end of the resistor R2 and the negative input end of the comparator; the second end of the resistor R1 is connected to the voltage VCM; and the second end of the resistor R2 is connected to the voltage VCMH.

[0012] Preferably, the operational amplification module comprises MOS tube M4, MOS tube M5, MOS tube M6, MOS tube M7, MOS tube M8, MOS tube M9, MOS tube M10, variable capacitor C1, variable capacitor C2 and high resistance unit; the gate of the MOS tube M4 is connected with voltage VFB, the drain of the MOS tube M4 is connected with the drain of the MOS tube M6, the gate of the MOS tube M6 and the gate of the MOS tube M7, the source of the MOS tube M4 is connected with power supply and the source of the MOS tube M5; the gate of the MOS tube M5 is connected with the output of the high resistance bias circuit, the drain of the MOS tube M5 is connected with the drain of the MOS tube M7, the gate of the MOS tube M8 and the gate of the MOS tube M9; the source of the MOS tube M6 and the source of the MOS tube M7 are connected with ground GND; the drain of the MOS tube M8 is connected with the gate of the MOS tube M10 and power supply, the source of the MOS tube M8 is connected with ground GND; the drain of the MOS tube M10 is connected with power supply, the source of the MOS tube M10 is connected with the drain of the MOS tube M9, the first end of the variable capacitor C1, the first end of the high resistance unit and the rear stage circuit; the source of the MOS tube M9 is connected with ground GND; the second end of the variable capacitor C1 is connected with the first end of the variable capacitor C2 and the second end of the high resistance unit; the second end of the variable capacitor C2 is connected with ground GND;

[0013] The high resistance unit is resistance RH with resistance greater than preset resistance value, or MOS tubes in series or diodes in series.

[0014] Preferably, the operational amplification module comprises first operational amplifier, second operational amplifier, variable capacitor C9, variable capacitor C10, variable capacitor C11, first high resistance unit and second high resistance unit; the positive input of the first operational amplifier and the positive input of the second operational amplifier are connected with the output of the high resistance bias circuit; the negative input of the first operational amplifier is connected with the first end of the variable capacitor C9, the first end of the variable capacitor C11 and the first end of the first high resistance unit, the output of the first operational amplifier is connected with the second end of the variable capacitor C9, the second end of the first high resistance unit and the rear stage circuit; the negative input of the second operational amplifier is connected with the first end of the variable capacitor C10, the second end of the variable capacitor C11 and the first end of the second high resistance unit, the output of the second operational amplifier is connected with the second end of the variable capacitor C10, the second end of the second high resistance unit and the rear stage circuit.

[0015] The first high resistance unit and the second high resistance unit are resistance RH with resistance greater than preset resistance value, or MOS tubes in series or diodes in series.

[0016] Preferably, the operational amplification module comprises a four-port operational amplifier, a variable capacitor C12, a variable capacitor C13, a variable capacitor C14, a third high resistance unit and a fourth high resistance unit; a first non-inverting input terminal of the four-port operational amplifier is connected to a first terminal of the variable capacitor C12 and a first terminal of the variable capacitor C14, a second non-inverting input terminal of the four-port operational amplifier is connected to an output terminal of the high resistance biasing circuit, a first inverting input terminal of the four-port operational amplifier is connected to a second terminal of the variable capacitor C13 and a second terminal of the variable capacitor C14, a second inverting input terminal of the four-port operational amplifier is connected to a ground signal of the microphone equivalent model, an inverting output terminal of the four-port operational amplifier is connected to a second terminal of the variable capacitor C12 and a subsequent circuit, and a non-inverting output terminal of the four-port operational amplifier is connected to a second terminal of the variable capacitor C13 and the subsequent circuit; the variable capacitor C12 is connected in parallel with the third high resistance unit, and the variable capacitor C13 is connected in parallel with the fourth high resistance unit.

[0017] The third high resistance unit and the fourth high resistance unit are a resistor RH with a resistance value greater than a preset resistance value, or a plurality of series-connected MOS tubes, or a plurality of series-connected diodes.

[0018] The present application has the following advantages:

[0019] 1) The listening wake-up circuit of the present application can wake up the operational amplification module in the AFE circuit in time to amplify the microphone signal when the microphone outputs an effective signal. This makes the AFE system in the listening standby mode be able to turn off the operational amplification module, so as to maintain the listening wake-up circuit with extremely low power consumption, which undoubtedly reduces the power consumption of the AFE system.

[0020] 2) The present application adds a high resistance biasing circuit to the microphone output end to modulate the microphone output direct current DC bias. Compared with the method of changing the microphone output direct current DC bias by using a source follower in the traditional circuit, the scheme of the present application saves MOS tubes and can realize lower noise.

[0021] 3) The operational amplification module of the present application adopts variable capacitor feedback. The variable capacitor does not contribute additional noise and has lower power consumption. Compared with other AFE circuits adopting resistance feedback, the present application has better noise characteristics and lower power consumption. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 It is a circuit schematic diagram in an embodiment of the present application.

[0023] Figure 2 It is a listening wake-up circuit schematic diagram.

[0024] Figure 3 It is a high resistance biasing circuit schematic diagram.

[0025] Figure 4Circuit schematic diagram of an operational amplifier module in an embodiment;

[0026] Figure 5 Circuit schematic diagram of an operational amplifier module in another embodiment;

[0027] Figure 6 Circuit schematic diagram of an operational amplifier module in yet another embodiment. DETAILED DESCRIPTION

[0028] The technical solutions of the present application will be described in detail below with reference to embodiments. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative effort belong to the scope of the present application.

[0029] Referring to Figures 1-6 wherein AOUT represents the output signal of the operational amplifier; Figure 1 and Figure 2 VP in the above equation represents the positive input signal of the band-pass filter; Figure 1 and Figure 2 VN in the above equation represents the negative input signal of the band-pass filter; VOUTP represents the positive output signal of the operational amplifier module; VOUTN represents the negative output signal of the operational amplifier module; VDD represents the power supply; M1 and M2 are both MOS tubes; the remaining abbreviations have corresponding explanations in the following or have meanings known to those skilled in the art (which can be found in corresponding technical manuals or textbooks) and are not explained here one by one.

[0030] The present application provides a technical solution: a microphone pre-AFE circuit with a listening wake-up function, comprising a microphone equivalent model, the output end of the microphone equivalent model is connected with a high-resistance biasing circuit and a listening wake-up circuit, the output end of the high-resistance biasing circuit is connected with an operational amplifier module, and the output end of the operational amplifier module is connected with a post-stage circuit.

[0031] When the microphone pre-AFE circuit is in a normal working mode, only the operational amplifier module works normally, and the listening wake-up circuit does not work; when the microphone pre-AFE circuit enters a listening standby mode, the operational amplifier module does not work, and the microphone pre-AFE circuit maintains the listening wake-up circuit with a power consumption lower than that in the normal working mode; when the listening wake-up circuit outputs a high FLAG signal, the operational amplifier module is woken up to amplify the microphone signal.

[0032] In the embodiment, only the operational amplifier module works when the circuit is in normal working mode, and the monitoring wake-up circuit does not work. The operational amplifier module realizes accurate amplification of the microphone signal. When the circuit enters the monitoring standby mode, the operational amplifier module will be closed, and the circuit maintains the monitoring wake-up circuit with extremely low power consumption. When the FLAG signal output by the monitoring wake-up circuit is high, it means that the microphone has monitored useful sound, and at this time the operational amplifier module will be woken up to amplify the microphone signal. Because of the existence of the monitoring wake-up circuit, the AFE circuit of the present application can standby with extremely low power consumption without affecting the main function.

[0033] The monitoring wake-up circuit is composed of a source follower circuit, a band-pass filter, a variable gain amplifier, a high-pass filter and a comparator. The specific principle is as follows: the DC voltage of the microphone output signal is lifted through the source follower circuit so that the band-pass filter can work normally. The AC component VIN of the microphone signal is amplified by the variable gain amplifier circuit, and the resistance R3 has the same resistance value as R5. The amplification factor of the variable gain amplifier is 2*R3 / R4. The high-pass filter processes the output signal of the variable gain amplifier to block the DC voltage. When the AC component VIN of the microphone output signal is amplified by the variable gain amplifier and is greater than VCMH-VCM, the comparator will output a high level. The FLAG signal judgment basis is as follows:

[0034] When the system receives the high level FLAG signal, the operational amplifier module can be started to work, the operational amplifier module accurately amplifies the microphone signal, and ensures the THD and noise performance of the signal. The source follower circuit is connected to the microphone to realize the level shift function, and also provides a certain driving ability to drive the subsequent band-pass filter. The band-pass filter filters out the low-frequency noise and high-frequency interference signals and transmits the signal to the variable gain amplifier. The variable gain amplifier amplifies the signal by a certain multiple, and then processes the signal through the high-pass filter to block the DC voltage and change the DC voltage to voltage VCMH and voltage VCM, voltage VCMH> voltage VCM. The high-pass filter is connected to the input end of the comparator. The output result of the comparator can be calculated as follows:

[0035] FLAG is the output of the comparator, and FLAG is 0 or 1, representing low level and high level respectively. VIN is the AC component of the microphone output signal, A is the amplification factor of the variable gain amplifier, and B is the gain coefficient of the band-pass filter. When the AC component of the microphone output signal exceeds (VCMH-VCM) / A*B, the comparator outputs high. The user can change the amplification factor of the variable gain amplifier to control the threshold of the AFE circuit automatic wake-up.

[0036] In some embodiments, the listening wake-up circuit includes a source follower circuit, the input of which is connected to a microphone equivalent model, the output of which is connected to a bandpass filter, the output of which is connected to a variable gain amplifier, the output of which is connected to a high-pass filter, and the output of which is connected to a comparator for outputting a FLAG signal.

[0037] In some embodiments, the high-impedance bias circuit includes diode D1, diode D2, transistor Q1, transistor Q2, and MOSFET M3; the anode of diode D1 is connected to the microphone equivalent model, the drain of MOSFET M3, and the emitter of transistor Q1, and the cathode of diode D1 is connected to the base and collector of transistor Q1; the source and gate of MOSFET M3 are connected to ground GND; the collector of transistor Q1 is connected to the anode of diode D2; the anode of diode D2 is connected to the power supply and the emitter of transistor Q2, and the cathode of diode D2 is connected to ground GND; the collector of transistor Q2 is connected to the base of transistor Q2 and ground GND.

[0038] In this embodiment, as Figure 3 As shown, the current source Idc forward conducts diode D2 and transistor Q2, making the voltage at VX equal to the PN junction turn-on voltage, approximately 0.7V. The microphone output voltage at VY is determined by the voltage divider between the turn-off resistors of diode D1 and MOSFET M3. By adjusting the area of ​​diode D1 and the width and length of MOSFET M3, the DC voltage at VY can be controlled.

[0039] In some embodiments, the source follower circuit is a differential structure, with the non-inverting input terminal of the source follower circuit connected to the output terminal of the microphone equivalent model, the inverting input terminal of the source follower circuit connected to ground (GND), and the differential output terminal of the source follower circuit connected to the input terminal of the bandpass filter.

[0040] In some embodiments, the band-pass filter is a fully differential structure, comprising resistors R6, R7, R8, R9, R10, R11, R12, R13, R14, capacitors C5, C6, C7, C8, C9, an amplifier AMP4 and an amplifier AMP5; a first end of the resistors R13 and R14 is connected to a differential output end of a source follower circuit, a second end of the resistor R13 is connected to a first end of the capacitor C7 and the capacitor C7, a second end of the resistor R14 is connected to a first end of the capacitor C8 and a second end of the capacitor C9; a second end of the capacitor C7 is connected to a first end of the resistor R11 and a positive input end of the amplifier AMP4; a second end of the capacitor C8 is connected to a first end of the resistor R11 and a positive input end of the amplifier AMP5; a second end of the resistor R11 is connected to a second end of the resistor R12; a negative input end of the amplifier AMP4 is connected to a first end of the resistor R10 and the resistor R8, an output end of the amplifier AMP4 is connected to a second end of the resistor R8 and a first end of the capacitor C5; a negative input end of the amplifier AMP5 is connected to a second end of the resistor R10 and a first end of the resistor R9, an output end of the amplifier AMP5 is connected to a second end of the resistor R9 and a first end of the capacitor C6; a second end of the capacitor C5 is connected to an input end of a variable gain amplifier and a first end of the resistor R6; a second end of the capacitor C6 is connected to an input end of the variable gain amplifier and a first end of the resistor R7; a second end of the resistor R6 is connected to a second end of the resistor R7.

[0041] In some embodiments, the variable gain amplifier is a fully differential structure, comprising an amplifier AMP2, an amplifier AMP3, adjustable resistors R3, R4 and R5; a positive input end of the amplifier AMP2 is connected to an output end of the band-pass filter, a negative input end of the amplifier AMP2 is connected to first ends of the adjustable resistors R3 and R4, an output end of the amplifier AMP2 is connected to a second end of the adjustable resistor R3 and an input end of the high-pass filter; a second end of the adjustable resistor R4 is connected to a negative input end of the amplifier AMP3 and a first end of the adjustable resistor R5; a positive input end of the amplifier AMP3 is connected to the output end of the band-pass filter, an output end of the amplifier AMP3 is connected to a second end of the adjustable resistor R5 and the input end of the high-pass filter.

[0042] In some embodiments, the high-pass filter is a fully differential structure, comprising capacitors C3, C4, resistors R1 and R2; a first end of the capacitor C3 is connected to an output end of the variable gain amplifier, a second end of the capacitor C3 is connected to a first end of the resistor R1 and a positive input end of a comparator; a first end of the capacitor C4 is connected to the output end of the variable gain amplifier, a second end of the capacitor C4 is connected to a first end of the resistor R2 and a negative input end of the comparator; a second end of the resistor R1 is connected to a voltage VCM; a second end of the resistor R2 is connected to a voltage VCMH.

[0043] In the embodiment, the high-pass filter isolates the output DC signal of the variable gain amplifier, and the positive and negative input terminals of the comparator are respectively set with different voltage values of DC voltage VCM and VCMH.

[0044] In some embodiments, the operational amplifier module comprises MOS tube M4, MOS tube M5, MOS tube M6, MOS tube M7, MOS tube M8, MOS tube M9, MOS tube M10, variable capacitor C1, variable capacitor C2 and high resistance unit; the gate of the MOS tube M4 is connected with voltage VFB, the drain of the MOS tube M4 is connected with the drain of the MOS tube M6, the gate of the MOS tube M6 and the gate of the MOS tube M7, the source of the MOS tube M4 is connected with power supply and the source of the MOS tube M5; the gate of the MOS tube M5 is connected with the output end of the high resistance bias circuit, the drain of the MOS tube M5 is connected with the drain of the MOS tube M7, the gate of the MOS tube M8 and the gate of the MOS tube M9; the sources of the MOS tube M6 and the MOS tube M7 are connected with ground GND; the drain of the MOS tube M8 is connected with the gate of the MOS tube M10 and power supply, the source of the MOS tube M8 is connected with ground GND; the drain of the MOS tube M10 is connected with power supply, the source of the MOS tube M10 is connected with the drain of the MOS tube M9, the first end of the variable capacitor C1, the first end of the high resistance unit and the rear stage circuit; the source of the MOS tube M9 is connected with ground GND; the second end of the variable capacitor C1 is connected with the first end of the variable capacitor C2 and the second end of the high resistance unit; the second end of the variable capacitor C2 is connected with ground GND.

[0045] The high resistance unit is a resistor RH with resistance greater than a preset resistance value, or a plurality of series connected MOS tubes or a plurality of series connected diodes.

[0046] In the embodiment, as shown in Figure 4 the AC gain of the operational amplifier AMP1 can be changed by the variable capacitors C1 and C2. The DC voltage value at VFB can be determined by the high resistance unit. The high resistance unit can be implemented by a resistor RH with resistance greater than a preset resistance value, or by MOS tubes or diodes.

[0047] In some embodiments, the operational amplifier module comprises a first operational amplifier, a second operational amplifier, a variable capacitor C9, a variable capacitor C10, a variable capacitor C11, a first high resistance unit and a second high resistance unit; the positive input terminals of the first operational amplifier and the second operational amplifier are connected to the output terminal of the high resistance bias circuit; the negative input terminal of the first operational amplifier is connected to the first terminal of the variable capacitor C9, the variable capacitor C11 and the first high resistance unit, and the output terminal of the first operational amplifier is connected to the second terminal of the variable capacitor C9, the second terminal of the first high resistance unit and the subsequent circuit; the negative input terminal of the second operational amplifier is connected to the first terminal of the variable capacitor C10, the second terminal of the variable capacitor C11 and the first terminal of the second high resistance unit, and the output terminal of the second operational amplifier is connected to the second terminal of the variable capacitor C10, the second terminal of the second high resistance unit and the subsequent circuit.

[0048] The first high resistance unit and the second high resistance unit are a resistor RH with a resistance value greater than a preset resistance value, or a plurality of MOS tubes connected in series, or a plurality of diodes connected in series.

[0049] In the embodiment, as shown in Figure 5 The operational amplifier module can be composed of two operational amplifiers; C9, C10 and C11 are variable capacitors for determining the amplification factor of the operational amplifier; the two high resistance units determine the DC voltage of the negative input terminal of the operational amplifier. The high resistance unit can be realized by a resistor RH with a resistance value greater than a preset resistance value, or by a MOS tube or a diode.

[0050] In some embodiments, the operational amplifier module comprises a four-port operational amplifier, a variable capacitor C12, a variable capacitor C13, a variable capacitor C14, a third high resistance unit and a fourth high resistance unit; the first non-inverting input terminal of the four-port operational amplifier is connected to the first terminals of the variable capacitor C12 and the variable capacitor C14, the second non-inverting input terminal of the four-port operational amplifier is connected to the output terminal of the high resistance bias circuit, the first inverting input terminal of the four-port operational amplifier is connected to the first terminal of the variable capacitor C13 and the second terminal of the variable capacitor C14, the second inverting input terminal of the four-port operational amplifier is connected to the ground signal of the microphone equivalent model, the inverting output terminal of the four-port operational amplifier is connected to the second terminal of the variable capacitor C12 and the subsequent circuit, and the non-inverting output terminal of the four-port operational amplifier is connected to the second terminal of the variable capacitor C13 and the subsequent circuit; the variable capacitor C12 is connected in parallel with the third high resistance unit, and the variable capacitor C13 is connected in parallel with the fourth high resistance unit.

[0051] The third high resistance unit and the fourth high resistance unit are a resistor RH with a resistance value greater than a preset resistance value, or a plurality of MOS tubes connected in series, or a plurality of diodes connected in series.

[0052] In the embodiment, as shown in Figure 6As shown, the operational amplification module can be implemented by a four-port operational amplifier, and the circuit is composed of one four-port operational amplifier, adjustable capacitors C14, C12, C13, and two high-resistance units. The capacitance values of the adjustable capacitors C12 and C13 are generally set to be consistent, so that the overall gain of the operational amplification module is 2*C14 / C12. One high-resistance unit is connected in parallel with the C12 capacitor, and the other high-resistance unit is connected in parallel with the C13 capacitor. The high-resistance unit can be implemented by using a resistor RH with a resistance value greater than a preset resistance value, or by using a MOS tube or a diode. The number of MOS tubes or diodes connected in series can be changed according to actual conditions.

[0053] The above description is only preferred embodiments of the present application, and it should be understood that the present application is not limited to the forms disclosed herein, and should not be considered as excluding other embodiments, but can be used in various other combinations, modifications and environments, and can be modified within the scope of the concepts described herein by using the above teachings or related technical or knowledge. Any modification and change made by those skilled in the art without departing from the spirit and scope of the present application shall be within the protection scope of the claims of the present application.

Claims

1. A microphone preamplifier AFE circuit with listening and wake-up function, characterized in that: The system includes a microphone equivalent model, the output of which is connected to a high-impedance bias circuit and a listening wake-up circuit. The output of the high-impedance bias circuit is connected to an operational amplifier module, and the output of the operational amplifier module is connected to a subsequent stage circuit. The operational amplifier module amplifies or attenuates the microphone signal proportionally through feedback from a variable capacitor. When the microphone preamplifier (AFE) circuit is in normal operating mode, only the operational amplifier module works normally, and the monitoring wake-up circuit does not work. When the microphone preamplifier AFE circuit enters the monitoring standby mode, the operational amplifier module does not work, and the microphone preamplifier AFE circuit maintains the monitoring wake-up circuit with a power consumption lower than that in normal operating mode. When the monitoring wake-up circuit outputs a high FLAG signal, it wakes up the operational amplifier module to amplify the microphone signal. The listening wake-up circuit includes a source follower circuit. The input of the source follower circuit is connected to a microphone equivalent model. The output of the source follower circuit is connected to a bandpass filter. The output of the bandpass filter is connected to a variable gain amplifier. The output of the variable gain amplifier is connected to a high-pass filter. The output of the high-pass filter is connected to a comparator. The comparator is used to output a FLAG signal. The high-impedance bias circuit includes diodes D1 and D2, transistors Q1 and Q2, and MOSFET M3. The anode of diode D1 is connected to the microphone equivalent model, the drain of MOSFET M3, and the emitter of transistor Q1; the cathode of diode D1 is connected to the base and collector of transistor Q1. The source and gate of MOSFET M3 are connected to ground (GND). The collector of transistor Q1 is connected to the anode of diode D2. The anode of diode D2 is connected to the power supply and the emitter of transistor Q2; the cathode of diode D2 is connected to ground (GND). The collector of transistor Q2 is connected to the base of transistor Q2 and ground (GND). The source follower circuit is a differential structure. The non-inverting input terminal of the source follower circuit is connected to the output terminal of the microphone equivalent model, the inverting input terminal of the source follower circuit is connected to ground (GND), and the differential output terminal of the source follower circuit is connected to the input terminal of the bandpass filter. The bandpass filter is a fully differential structure, including resistors R6, R7, R8, R9, R10, R11, R12, R13, and R14; capacitors C5, C6, C7, C8, and C9; amplifiers AMP4 and AMP5; the first terminals of resistors R13 and R14 are connected to the differential output terminal of the source follower circuit; the second terminal of resistor R13 is connected to capacitors C7 and C7; the second terminal of resistor R14 is connected to the first terminal of capacitor C8 and the second terminal of capacitor C9; the second terminal of capacitor C7 is connected to the first terminal of resistor R11 and the positive input terminal of amplifier AMP4; the second terminal of capacitor C8 is connected to the first terminal of resistor R11 and... The positive input terminal of amplifier AMP5; the second terminal of resistor R11 is connected to the second terminal of resistor R12; the negative input terminal of amplifier AMP4 is connected to the first terminals of resistors R10 and R8, and the output terminal of amplifier AMP4 is connected to the second terminal of resistor R8 and the first terminal of capacitor C5; the negative input terminal of amplifier AMP5 is connected to the second terminal of resistor R10 and the first terminal of resistor R9, and the output terminal of amplifier AMP5 is connected to the second terminal of resistor R9 and the first terminal of capacitor C6; the second terminal of capacitor C5 is connected to the input terminal of variable gain amplifier and the first terminal of resistor R6; the second terminal of capacitor C6 is connected to the input terminal of variable gain amplifier and the first terminal of resistor R7; the second terminal of resistor R6 is connected to the second terminal of resistor R7. The variable gain amplifier is a fully differential structure, including amplifier AMP2, amplifier AMP3, adjustable resistors R3, R4, and R5. The positive input terminal of amplifier AMP2 is connected to the output terminal of a bandpass filter, the negative input terminal of amplifier AMP2 is connected to the first terminals of adjustable resistors R3 and R4, and the output terminal of amplifier AMP2 is connected to the second terminal of adjustable resistor R3 and the input terminal of a high-pass filter. The second terminal of adjustable resistor R4 is connected to the negative input terminal of amplifier AMP3 and the first terminal of adjustable resistor R5. The positive input terminal of amplifier AMP3 is connected to the output terminal of a bandpass filter, and the output terminal of amplifier AMP3 is connected to the second terminal of adjustable resistor R5 and the input terminal of a high-pass filter. The high-pass filter is a fully differential structure, including capacitor C3, capacitor C4, resistor R1, and resistor R2. The first terminal of capacitor C3 is connected to the output terminal of the variable gain amplifier, and the second terminal of capacitor C3 is connected to the first terminal of resistor R1 and the positive input terminal of the comparator. The first terminal of capacitor C4 is connected to the output terminal of the variable gain amplifier, and the second terminal of capacitor C4 is connected to the first terminal of resistor R2 and the negative input terminal of the comparator. The second terminal of resistor R1 is connected to voltage VCM, and the second terminal of resistor R2 is connected to voltage VCMH.

2. The microphone preamplifier AFE circuit with listening and wake-up function according to claim 1, characterized in that: The operational amplifier module includes MOSFETs M4, M5, M6, M7, M8, M9, and M10, variable capacitors C1 and C2, and a high-impedance unit. The gate of MOSFET M4 is connected to voltage VFB, and its drain is connected to the drain, gate, and gate of MOSFET M6 and MOSFET M7. The source of MOSFET M4 is connected to the power supply and the source of MOSFET M5. The gate of MOSFET M5 is connected to the output of the high-impedance bias circuit, and its drain is connected to the drain of MOSFET M7 and the gate of MOSFET M8. The gate of MOSFET M9 is connected to the gate of MOSFET M6 and MOSFET M7; the sources of MOSFET M6 and MOSFET M7 are connected to ground (GND); the drain of MOSFET M8 is connected to the gate of MOSFET M10 and the power supply, and the source of MOSFET M8 is connected to ground (GND); the drain of MOSFET M10 is connected to the power supply, and the source of MOSFET M10 is connected to the drain of MOSFET M9, the first terminal of variable capacitor C1, the first terminal of high-impedance unit, and the subsequent circuit; the source of MOSFET M9 is connected to ground (GND); the second terminal of variable capacitor C1 is connected to the first terminal of variable capacitor C2 and the second terminal of high-impedance unit; the second terminal of variable capacitor C2 is connected to ground (GND). The high-resistance unit is a resistor RH with a resistance value greater than a preset resistance value, or multiple MOS transistors or multiple diodes connected in series.

3. The microphone preamplifier AFE circuit with listening and wake-up function according to claim 1, characterized in that: The operational amplifier module includes a first operational amplifier, a second operational amplifier, variable capacitors C9, C10, and C11, a first high-impedance unit, and a second high-impedance unit. The positive input terminals of the first and second operational amplifiers are connected to the output terminal of the high-impedance bias circuit. The negative input terminal of the first operational amplifier is connected to the first terminal of the variable capacitors C9 and C11 and the first terminal of the first high-impedance unit. The output terminal of the first operational amplifier is connected to the second terminal of the variable capacitor C9, the second terminal of the first high-impedance unit, and the subsequent stage circuit. The negative input terminal of the second operational amplifier is connected to the first terminal of the variable capacitor C10, the second terminal of the variable capacitor C11, and the first terminal of the second high-impedance unit. The output terminal of the second operational amplifier is connected to the second terminal of the variable capacitor C10, the second terminal of the second high-impedance unit, and the subsequent stage circuit. The first high-resistance unit and the second high-resistance unit are resistors RH with a resistance value greater than a preset resistance value, or multiple MOS transistors or multiple diodes connected in series.

4. The microphone preamplifier AFE circuit with listening and wake-up function according to claim 1, characterized in that: The operational amplifier module includes a four-port operational amplifier, variable capacitors C12, C13, and C14, a third high-impedance unit, and a fourth high-impedance unit. The first non-inverting input of the four-port operational amplifier is connected to the first terminals of variable capacitors C12 and C14; the second non-inverting input is connected to the output of a high-impedance bias circuit; the first inverting input is connected to the first terminal of variable capacitor C13 and the second terminal of variable capacitor C14; the second inverting input is connected to the ground signal of the microphone equivalent model; the inverting output is connected to the second terminal of variable capacitor C12 and the subsequent stage circuit; the non-inverting output is connected to the second terminal of variable capacitor C13 and the subsequent stage circuit; the third high-impedance unit is connected in parallel with variable capacitor C12, and the fourth high-impedance unit is connected in parallel with variable capacitor C13. The third and fourth high-resistance units are resistors RH with a resistance value greater than a preset resistance value, or multiple MOS transistors or multiple diodes connected in series.

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