Single-ended to differential microphone circuit

Abstract

The application provides a single-ended-to-differential microphone circuit, which comprises a power supply end for inputting a first bias voltage, a microphone capacitor, a coupling capacitor, a first primary amplifier, a second primary amplifier, a signal processing module, a current-shared amplifier, a positive end feedback resistor, a positive end feedback capacitor, a negative end feedback resistor and a negative end feedback capacitor, wherein the microphone capacitor is connected to an input end of the first primary amplifier, the coupling capacitor is connected to an input end of the second primary amplifier, the signal processing module is used for adjusting output signals of the first primary amplifier and the second primary amplifier into target differential signals with equal amplitudes and opposite phases, and outputting the target differential signals to the current-shared amplifier. Compared with the prior art, the single-ended-to-differential microphone circuit of the application can realize single-ended-to-differential conversion of signals by using a current-shared amplifier with a small input common-mode voltage range and small noise, thereby being beneficial to improving the signal-to-noise ratio of the circuit.

Description

[Technical Field]

[0001] This invention relates to the field of electroacoustic conversion, and more particularly to a single-ended to differential microphone circuit. [Background Technology]

[0002] MEMS (Microelectro Mechanical Systems) microphones are microphones manufactured based on MEMS sensor technology. They feature improved noise cancellation performance, good radio frequency performance, and electromagnetic interference suppression capabilities, and are widely used in various electronic products such as smartphones, wired headphones, tablets, and laptops. To reduce external electromagnetic interference and improve signal transmission quality, related technologies typically convert the single-ended signal output of MEMS microphones into differential signals for transmission.

[0003] like Figure 1 As shown, in a traditional single-ended to differential microphone circuit, the output of the MEMS microphone is directly connected to the positive input of the fully differential amplifier Amp, and the compensation capacitor C... DMY The signal is connected to the negative input of the fully differential amplifier Amp. However, due to the limitations of the MEMS microphone's structure, the substrate of its sensor generates a large parasitic capacitance to ground. This causes the amplitude of the signal output from the substrate to be smaller than the amplitude of the signal output from the sensor's signal terminal. In the equivalent circuit, the signal output from the substrate is transmitted to the negative input of the fully differential amplifier Amp, while the signal from the sensor's signal terminal is transmitted to the positive input of the fully differential amplifier Amp. Therefore, the signal amplitudes at the positive and negative input terminals of the fully differential amplifier are different and opposite in phase, resulting in non-ideal differential signals. This leads to a large amplitude of the common-mode voltage at the positive and negative input terminals. This requires the fully differential amplifier Amp to be an amplifier with a large input common-mode voltage range to ensure that the fully differential amplifier Amp can work properly. However, such fully differential amplifiers usually have high noise, which is not conducive to improving the signal-to-noise ratio of the circuit.

[0004] Therefore, it is necessary to provide a new single-ended to differential microphone circuit to solve the above-mentioned technical problems. [Summary of the Invention]

[0005] The purpose of this invention is to provide a single-ended to differential microphone circuit that can use a current-shared amplifier with a small input common-mode voltage range and low noise to achieve single-ended to differential signal conversion, which is beneficial to improving the signal-to-noise ratio of the circuit.

[0006] To achieve the above objectives, the present invention provides a single-ended to differential microphone circuit, comprising a power supply terminal for inputting a first bias voltage, a microphone capacitor, a coupling capacitor, a first primary amplifier, a second primary amplifier, a signal processing module, a current-shared amplifier, a positive feedback resistor, a positive feedback capacitor, a negative feedback resistor, and a negative feedback capacitor; wherein, the microphone capacitor is formed equivalently when the microphone is connected to the single-ended to differential microphone circuit;

[0007] The power supply terminal is connected to the bias voltage input terminal of the microphone capacitor, and the output terminal of the microphone capacitor is connected to the input terminal of the first primary amplifier.

[0008] The positive terminal of the coupling capacitor is grounded or connected to the bias voltage input terminal. When the positive terminal of the coupling capacitor is connected to the bias voltage input terminal, the microphone circuit further includes a first bias resistor connected in series between the power supply terminal and the bias voltage input terminal. The negative terminal of the coupling capacitor is connected to the input terminal of the second primary amplifier.

[0009] The output terminals of the first primary amplifier and the second primary amplifier are respectively connected to the positive and negative input terminals of the signal processing module. The positive and negative output terminals of the signal processing module are respectively connected to the positive and negative input terminals of the current common amplifier. The signal processing module adjusts the output signals of the first primary amplifier and the second primary amplifier into target differential signals with equal amplitude and opposite phase, and outputs the target differential signals to the current common amplifier.

[0010] The positive feedback resistor and the positive feedback capacitor are both connected in parallel between the positive input terminal and the negative output terminal of the current-shared amplifier, and the negative feedback resistor and the negative feedback capacitor are both connected in parallel between the negative input terminal and the positive output terminal of the current-shared amplifier.

[0011] Furthermore, the signal processing module includes a signal multiplier, which is specifically used for:

[0012] The difference signal is obtained by subtracting the output signal of the second primary amplifier from the output signal of the first primary amplifier.

[0013] The difference signal is inverted to obtain an inverted difference signal, and the difference signal and the inverted difference signal constitute the target difference signal;

[0014] The difference signal is output from the positive output terminal of the signal processing module, and the inverted difference signal is output from the negative output terminal of the signal processing module.

[0015] Furthermore, the signal multiplier includes four switched capacitors, each of which includes two first switches, two second switches, and a capacitor. The four switched capacitors are respectively a first switched capacitor, a second switched capacitor, a third switched capacitor, and a fourth switched capacitor.

[0016] Wherein, the positive terminal of the first switched capacitor is connected to the positive input terminal of the signal processing module through a first switch and to the positive output terminal of the signal processing module through a second switch; the negative terminal of the capacitor is connected to the negative input terminal of the signal processing module through another first switch and to the input common-mode voltage through another second switch.

[0017] The positive terminal of the second switched capacitor is connected to the positive input terminal of the signal processing module through one of the first switches and to the input common-mode voltage through one of the second switches. The negative terminal of the capacitor is connected to the negative input terminal of the signal processing module through another of the first switches and to the negative output terminal of the signal processing module through another of the second switches.

[0018] The positive terminal of the third switched capacitor is connected to the positive output terminal of the signal processing module through a first switch and to the positive input terminal of the signal processing module through a second switch. The negative terminal of the capacitor is connected to the input common-mode voltage through another first switch and to the negative input terminal of the signal processing module through another second switch.

[0019] The positive terminal of the fourth switched capacitor is connected to the input common-mode voltage through a first switch and to the positive input terminal of the signal processing module through a second switch. The negative terminal of the capacitor is connected to the negative output terminal of the signal processing module through another first switch and to the negative input terminal of the signal processing module through another second switch.

[0020] All the first switches and the second switches are controlled by a set clock signal. When the clock signal is in the first phase, all the first switches are closed and all the second switches are open. When the clock signal is in the second phase opposite to the first phase, all the first switches are open and all the second switches are closed.

[0021] Furthermore, the single-ended to differential microphone circuit also includes a first chopper switch and a second chopper switch;

[0022] The first chopper switch is connected in series between the output terminal of the microphone and the input terminal of the first primary amplifier through one input terminal and one output terminal, and the first chopper switch is connected in series between the negative terminal of the coupling capacitor and the input terminal of the second primary amplifier through another input terminal and another output terminal.

[0023] The second chopper switch is connected in series between the output of the first primary amplifier and the positive input of the signal processing module through one input terminal and one output terminal, and the second chopper switch is connected in series between the output of the second primary amplifier and the negative input of the signal processing module through another input terminal and another output terminal.

[0024] Furthermore, the current-shared amplifier includes a bias current source, a first PMOS transistor, a second PMOS transistor, a first NMOS transistor, a second NMOS transistor, a third NMOS transistor, and a fourth NMOS transistor;

[0025] The source of the first PMOS transistor and the source of the second PMOS transistor are both connected to the output terminal of the bias current source. The gate of the first PMOS transistor is connected to the gate of the first NMOS transistor and together serve as the positive input terminal of the current-shared amplifier. The drain of the first PMOS transistor is connected to the drain of the first NMOS transistor and the gate of the third NMOS transistor and together serve as the negative output terminal of the current-shared amplifier.

[0026] The gate of the second PMOS transistor is connected to the gate of the second NMOS transistor and together serve as the negative input terminal of the current-shared amplifier. The drain of the second PMOS transistor is connected to the drain of the second NMOS transistor and the gate of the fourth NMOS transistor and together serve as the positive output terminal of the current-shared amplifier.

[0027] The source of the first NMOS transistor is connected to the drain of the third NMOS transistor, the source of the second NMOS transistor, and the drain of the fourth NMOS transistor.

[0028] The source of the third NMOS transistor and the source of the fourth NMOS transistor are both grounded.

[0029] Furthermore, the single-ended to differential microphone circuit also includes a second bias resistor and a third bias resistor;

[0030] One end of the second bias resistor is connected to the input terminal of the first primary amplifier, and the other end of the second bias resistor is used to input the second bias voltage; one end of the third bias resistor is connected to the input terminal of the second primary amplifier, and the other end of the third bias resistor is used to input the second bias voltage.

[0031] Furthermore, the first bias voltage is greater than the second bias voltage.

[0032] Furthermore, the resistance value of the first bias resistor is in the range of 100GΩ to 200GΩ.

[0033] Furthermore, the positive feedback resistor and the negative feedback resistor have the same resistance value, and the positive feedback capacitor and the negative feedback capacitor have the same capacitance value.

[0034] Compared with related technologies, the microphone circuit of the present invention includes a power supply terminal for inputting a first bias voltage, a microphone capacitor, a coupling capacitor, a first primary amplifier, a second primary amplifier, a signal processing module, a current common amplifier, a positive feedback resistor, a positive feedback capacitor, a negative feedback resistor, a negative feedback capacitor, a first output terminal, and a second output terminal. The microphone and the coupling capacitor are respectively connected to the input terminals of the first primary amplifier and the second primary amplifier. The output terminals of the first and second primary amplifiers are respectively connected to the positive and negative input terminals of the signal processing module. The positive and negative output terminals of the signal processing module are respectively connected to the positive and negative input terminals of the current common amplifier. The signal processing module adjusts the output signals of the first and second primary amplifiers into target differential signals with equal amplitude and opposite phase, and outputs the target differential signals to the current common amplifier. Thus, the signal processing module can output differential signals with equal amplitude and opposite phase, thereby utilizing a current common amplifier with a small input common-mode voltage range and low noise to achieve differential signal output, which is beneficial to improving the signal-to-noise ratio of the circuit. [Attached Image Description]

[0035] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort, wherein:

[0036] Figure 1 A circuit diagram of a single-ended to differential microphone circuit according to existing technology;

[0037] Figure 2 A circuit diagram of a single-ended to differential microphone circuit provided in an embodiment of the present invention;

[0038] Figure 3 A circuit diagram of a signal multiplier provided in an embodiment of the present invention;

[0039] Figure 4a for Figure 3 The circuit diagram shown is the equivalent circuit diagram of the signal multiplier when the clock signal is in the first phase.

[0040] Figure 4b for Figure 3 The circuit diagram shown is the equivalent circuit diagram of the signal multiplier when the clock signal is in the second phase.

[0041] Figure 5 Another circuit diagram of the single-ended to differential microphone circuit provided in the embodiment of the present invention;

[0042] Figure 6 The circuit diagram of a current-shared amplifier provided for an embodiment of the present invention.

Detailed Implementation Methods

[0043] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0044] Please see Figure 2 In the single-ended to differential microphone circuit of the present invention, the microphone circuit includes a power supply terminal V for inputting a first bias voltage. HCM Microphone capacitor C MEMS Coupling capacitor C AC First primary amplifier Amp1, second primary amplifier Amp2, signal processing module 10, current sharing amplifier CR-Amp, positive feedback resistor R FB1 Positive feedback capacitor C FB1 Negative feedback resistor R FB2 and the negative feedback capacitor C FB2 Wherein, the microphone capacitor C MEMS This is equivalent to connecting the microphone to the single-ended to differential microphone circuit.

[0045] The power supply terminal V HCM With the microphone capacitor C MEMS The bias voltage input terminal is connected to the microphone capacitor C, thereby providing the bias voltage input terminal for the microphone capacitor C. MEMS A first bias voltage is provided, which is a high-voltage bias voltage, for example, 13.8V, and the microphone capacitor C MEMS The output terminal is connected to the input terminal of the first primary amplifier Amp1.

[0046] The coupling capacitor C AC The positive terminal is grounded, and the coupling capacitor C ACThe negative terminal is connected to the input terminal of the second primary amplifier Amp2.

[0047] The output terminal of the first primary amplifier Amp1 is connected to the positive input terminal V of the signal processing module 10. I+ The output of the second primary amplifier Amp2 is connected to the negative input V of the signal processing module 10. I- The positive output terminal V of the signal processing module 10 is connected. O+ The negative output terminal V of the signal processing module 10 is connected to the positive input terminal of the current-sharing amplifier CR-Amp. O- The signal is connected to the negative input terminal of the current shared amplifier CR-Amp, so that the output signals of the first primary amplifier Amp1 and the second primary amplifier Amp2 are adjusted by the signal processing module 10 into target differential signals with equal amplitude and opposite phase, and the target differential signals are output to the current shared amplifier CR-Amp.

[0048] The positive terminal feedback resistor R FB1 and the positive feedback capacitor C FB1 Both are connected in parallel to the positive input and negative output V of the current-shared amplifier CR-Amp. OUTN Between, the negative terminal feedback resistor R FB2 and the negative feedback capacitor C FB2 Both are connected in parallel to the negative input terminal and the positive output terminal V of the current-shared amplifier CR-Amp. OUTP Between. Wherein, the positive terminal feedback resistor R FB1 and the negative terminal feedback resistor R FB2 The resistance values ​​can be the same, and the positive terminal feedback capacitor C FB1 and the negative feedback capacitor C FB2 The capacitance values ​​can be the same.

[0049] Therefore, in the single-ended to differential microphone circuit of this embodiment, the current-shared amplifier CR-Amp is a fully differential amplifier with dual-ended input and dual-ended output. The single-ended to differential conversion of the signal is achieved through the function of the current-shared amplifier CR-Amp. Specifically, the signal processing module 10 adjusts the output signals of the first primary amplifier Amp1 and the second primary amplifier Amp2 to target differential signals with equal amplitude and opposite phase. This ensures that the differential signals input to the fully differential amplifier in the subsequent circuit have equal amplitude and opposite phase, thereby reducing the input common-mode voltage range. Therefore, the fully differential amplifier in the subsequent circuit can be implemented using the current-shared amplifier CR-Amp, which has a smaller input common-mode voltage range. Compared to a fully differential amplifier with a larger input common-mode voltage range, the current-shared amplifier CR-Amp has lower noise, thus reducing the impact of its own noise on the entire circuit and improving the signal-to-noise ratio of the microphone circuit.

[0050] Furthermore, the signal processing module 10 of the present invention includes a signal multiplier, which is specifically used to subtract the output signal of the second primary amplifier Amp2 from the output signal of the first primary amplifier Amp1 to obtain a difference signal; then invert the difference signal to obtain an inverted difference signal, the difference signal and the inverted difference signal constituting the target differential signal; and is also used to output the difference signal from the positive output terminal of the signal processing module 10 and output the inverted difference signal from the negative output terminal of the signal processing module 10.

[0051] Therefore, the signal multiplier can adjust the output signals of the first primary amplifier Amp1 and the second primary amplifier Amp2 into target differential signals with equal amplitude and opposite phase. Furthermore, the amplitude difference between the two signals of the target differential signal is doubled compared to the amplitude difference before adjustment, which helps to reduce the impact of the current-shared amplifier in the subsequent circuit on the signal-to-noise ratio of the entire circuit.

[0052] More specifically, see Figure 3 In an embodiment of the present invention, the signal multiplier includes four switched capacitors, each of which includes two first switches S1, two second switches S2 and a capacitor. The four switched capacitors are respectively a first switched capacitor 101, a second switched capacitor 102, a third switched capacitor 103 and a fourth switched capacitor 104.

[0053] The positive terminal of capacitor C1 of the first switched capacitor 101 is connected to the positive input terminal V of the signal processing module 10 via a first switch S1. I+ And connected to the positive output terminal V of the signal processing module 10 via a second switch S2.O+ The negative terminal of capacitor C1 is connected to the negative input terminal V of signal processing module 10 via another first switch S1. I- And connected to the input common-mode voltage V via another second switch S2. CM .

[0054] The positive terminal of capacitor C2 of the second switched capacitor 102 is connected to the positive input terminal V of the signal processing module 10 via a first switch S1. I+ The input common-mode voltage V is connected via a second switch S2. CM The negative terminal of capacitor C2 is connected to the negative input terminal V of signal processing module 10 via another first switch S1. I- And connected to the negative output terminal V of the signal processing module 10 via another second switch S2. O- .

[0055] The positive terminal of capacitor C3 of the third switched capacitor 103 is connected to the positive output terminal V of the signal processing module 10 through a first switch S1. O+ And connected to the positive input terminal V of the signal processing module 10 via a second switch S2. I+ The negative terminal of capacitor C3 is connected to the input common-mode voltage V via another first switch S1. CM And connected to the negative input terminal V of the signal processing module 10 via another second switch S2. I- .

[0056] The positive terminal of capacitor C4 of the fourth switched capacitor 104 is connected to the input common-mode voltage V via a first switch S1. CM And connected to the positive input terminal V of the signal processing module 10 via a second switch S2. I+ The negative terminal of capacitor C4 is connected to the negative output terminal V of signal processing module 10 via another first switch S1. O- And connected to the negative input terminal V of the signal processing module 10 via another second switch S2. I- .

[0057] All first switches S1 and second switches S2 are controlled by a set clock signal. When the clock signal is a first phase S01, all first switches S1 are closed and all second switches S2 are open. When the clock signal is a second phase S02, which is opposite to the first phase S01, all first switches S1 are open and all second switches S2 are closed.

[0058] like Figure 4aand Figure 4b As shown, Figure 4a for Figure 3 The signal multiplier shown is the equivalent circuit diagram when the clock signal is the first phase S01. Figure 4b for Figure 3 The diagram shows the equivalent circuit of the signal multiplier when the clock signal is in the second phase S02. In the first phase S01, capacitors C1 and C2 are connected in parallel at the positive input terminal V of the signal processing module 10. I+ and negative input terminal V I- Between them, capacitors C3 and C4 are connected in series at the positive output terminal V of signal processing module 10. O+ and negative output terminal V O- Between these two points, the voltage difference across capacitor C1 and capacitor C2 is the positive input terminal V. I+ and negative input terminal V I- The voltage difference is the difference between the output signals of the first primary amplifier Amp1 and the second primary amplifier Amp2; and in the second phase S02, capacitors C1 and C2 are connected in series at the positive output terminal V of the signal processing module 10. O+ and negative output terminal V O- This superimposes the voltage difference between capacitor C1 and capacitor C2 at the first phase S01 onto the positive output terminal V. O+ and negative output terminal V O- Between. Therefore, the positive output terminal V O+ The signal is converted into the voltage difference across capacitor C1 plus the input common-mode voltage V. CM V O+ =V CM +V I+ -V I- ; Negative output terminal V O- The signal is converted into the input common-mode voltage V. CM Subtract the voltage difference across capacitor C2, i.e., V O- =V CM -(V I+ -V I- Therefore, the positive output terminal V O+ The signal and negative output terminal V O- The signal constitutes the target differential signal and is transmitted to the positive and negative input terminals of the current-shared amplifier CR-Amp, and V O+ -V O- =(V CM +V I+ -V I- )-(V CM -(V I+ -V I- ))=2(V I+ -VI- That is, the positive and negative amplitude difference of the target differential signal becomes twice the amplitude difference of the output signals of the first primary amplifier Amp1 and the second primary amplifier Amp2, thereby achieving a doubling of the amplitude difference.

[0059] The working principle of capacitors C3 and C4 is similar to that of capacitors C1 and C2. The control clock phases of the two are opposite to each other. Under the clock control of capacitors C1, C2, C3 and C4 with complementary phases, the positive and negative output terminals of the signal processing module 10 can obtain a continuous differential multiplication signal.

[0060] See Figure 5 In an embodiment of the present invention, the microphone circuit further includes a first chopper switch 11 and a second chopper switch 12.

[0061] The first chopper switch 11 is connected in series with the microphone capacitor C through an input terminal and an output terminal. MEMS Between the output terminal of the first primary amplifier Amp1 and the input terminal of the first chopper switch 11, the first chopper switch 11 is connected in series with the coupling capacitor C through another input terminal and another output terminal. AC Between the negative terminal of the amplifier and the input terminal of the second primary amplifier Amp2.

[0062] The second chopper switch 12 is connected in series with the output of the first primary amplifier Amp1 and the positive input V of the signal processing module 10 via an input terminal and an output terminal. I+ Between these two points, the second chopper switch 12 is connected in series with the output of the second primary amplifier Amp2 and the negative input V of the signal processing module 10 via another input terminal and another output terminal. I- between.

[0063] By performing Chopping processing on the signal using the first chopper switch 11 and the second chopper switch 12, low-frequency noise from the first primary amplifier Amp1 and the second primary amplifier Amp2 can be eliminated.

[0064] Continue reading Figure 5 In this embodiment, with Figure 2 The difference in the illustrated embodiment is that the coupling capacitor C AC The positive terminal can also be connected to the microphone capacitor C. MEMS The bias voltage input terminal, at this time, the microphone circuit also includes a series connection at the power supply terminal V. HCM The first bias resistor R between the bias voltage input terminal and the bias voltage input terminal B1 Among them, the first bias resistor R B1 These are high-resistance resistors, with resistance values ​​ranging from 100GΩ to 200GΩ.

[0065] Furthermore, the microphone circuit also includes a second bias resistor R. B2 and the third bias resistor R B3 .

[0066] The second bias resistor R B2 One end is connected to the input terminal of the first primary amplifier Amp1, and the second bias resistor R B2 The other end is used to input the second bias voltage V. B The third bias resistor R B3 One end of the resistor is connected to the input terminal of the second primary amplifier Amp2, and the third bias resistor R B3 The other end is used to input the second bias voltage V B The first bias voltage is greater than the second bias voltage V. B Second bias voltage V B This is a low voltage bias voltage, such as 0.8V.

[0067] Wherein, the second bias resistor R B2 and the third bias resistor R B3 The resistance values ​​are the same. The first bias resistor R B1 With the second bias resistor R B2 Third bias resistor R B3 The resistance values ​​can be the same or different; for example, they can all be 200GΩ.

[0068] like Figure 5 As shown, the sound signal originates from the microphone capacitor C. MEMS After input, it passes through the microphone capacitor C MEMS It is converted into an alternating current signal, and due to the first bias resistor R B1 The high impedance of the first chopper switch 11 allows the AC signal to be simultaneously input to the first primary amplifier Amp1 and the second primary amplifier Amp2 after passing through the first chopper switch 11, with the AC signals input to the first primary amplifier Amp1 and the second primary amplifier Amp2 having opposite phases. After chopping processing by the first chopper switch 11 and the second chopper switch 12, low-frequency noise in the first primary amplifier Amp1 and the second primary amplifier Amp2 can be eliminated. Then, the signal processing module 10 adjusts the signal processed by the second chopper switch 12 to obtain target differential signals with equal amplitude and opposite phase. Furthermore, it can amplify the amplitude of the target differential signal compared to before adjustment, thereby reducing the impact of the current-shared amplifier on the signal-to-noise ratio of the entire circuit and improving the signal-to-noise ratio.

[0069] Furthermore, when the closed-loop gain is 1, the capacitance values ​​of the positive and negative feedback capacitors in the prior art need to be set to be the same as those of the microphone capacitor C. MEMSThe capacitance values ​​are the same, but the microphone capacitor C MEMS The capacitance values ​​of the capacitors are usually small, resulting in small capacitance values ​​for the positive and negative feedback capacitors, which reduces the signal-to-noise ratio of the entire circuit. However, in this embodiment, by using the coupling capacitor C... AC Connected to the microphone capacitor C MEMS The bias voltage input terminal, and the power supply terminal V HCM and the microphone capacitor C MEMS A first bias resistor R is connected in series between the bias voltage input terminals. B1 Therefore, when the closed-loop gain is 1, the capacitance values ​​of the positive and negative feedback capacitors can be set to the microphone capacitance C. MEMS The capacitance value is doubled, which, compared to existing methods, increases the capacitance values ​​of the positive and negative feedback capacitors, thereby filtering out more noise from the current sharing amplifier itself and improving the signal-to-noise ratio of the entire microphone capacitor circuit.

[0070] See Figure 6 In an embodiment of the present invention, the current-shared amplifier CR-Amp includes a bias current source IB, a first PMOS transistor P1, a second PMOS transistor P2, a first NMOS transistor N1, a second NMOS transistor N2, a third NMOS transistor N3, and a fourth NMOS transistor N4.

[0071] The sources of the first PMOS transistor P1 and the second PMOS transistor P2 are both connected to the output terminal of the bias current source IB. The gate of the first PMOS transistor P1 is connected to the gate of the first NMOS transistor N1 and together they serve as the positive input terminal V of the current-shared amplifier CR-Amp. INP The drain of the first PMOS transistor P1 is connected to the drain of the first NMOS transistor N1 and the gate of the third NMOS transistor N3, and together they serve as the negative output terminal V of the current-shared amplifier CR-Amp. OUTN .

[0072] The gate of the second PMOS transistor P2 is connected to the gate of the second NMOS transistor N2 and together serve as the negative input terminal of the current-shared amplifier CR-Amp. The drain of the second PMOS transistor P2 is connected to the drain of the second NMOS transistor N2 and the gate of the fourth NMOS transistor N4 and together serve as the positive output terminal of the current-shared amplifier CR-Amp.

[0073] The source of the first NMOS transistor N1 is connected to the drain of the third NMOS transistor N3, the source of the second NMOS transistor N2, and the drain of the fourth NMOS transistor N4.

[0074] The source of the third NMOS transistor N3 and the source of the fourth NMOS transistor N4 are both grounded.

[0075] Therefore, for the aforementioned current-shared amplifier CR-Amp, the transconductance of the first PMOS transistor P1 and the first NMOS transistor N1, which serve as input transistors, is added together and then converted into a voltage at the negative output terminal V after passing through the third NMOS transistor N3, which serves as the load. OUTN The output voltage is obtained by adding the transconductances of the second PMOS transistor P2 and the second NMOS transistor N2, which act as input transistors, and then passing through the fourth NMOS transistor N4, which acts as a load, to form a voltage at the positive output terminal V. OUTP The output, thus doubling the transconductance under the same bias current, helps reduce the noise of the current-shared amplifier CR-Amp.

[0076] The above description is merely an embodiment of the present invention. It should be noted that those skilled in the art can make improvements without departing from the inventive concept of the present invention, but these improvements all fall within the protection scope of the present invention.

Claims

1. A single-ended to differential microphone circuit, characterized in that, It includes a power supply terminal for inputting a first bias voltage, a microphone capacitor, a coupling capacitor, a first primary amplifier, a second primary amplifier, a signal processing module, a current-shared amplifier, a positive feedback resistor, a positive feedback capacitor, a negative feedback resistor, and a negative feedback capacitor; wherein, the microphone capacitor is formed by connecting the microphone to the single-ended to differential microphone circuit in an equivalent manner; The power supply terminal is connected to the bias voltage input terminal of the microphone capacitor, and the output terminal of the microphone capacitor is connected to the input terminal of the first primary amplifier. The positive terminal of the coupling capacitor is grounded or connected to the bias voltage input terminal. When the positive terminal of the coupling capacitor is connected to the bias voltage input terminal, the single-ended to differential microphone circuit further includes a first bias resistor connected in series between the power supply terminal and the bias voltage input terminal. The negative terminal of the coupling capacitor is connected to the input terminal of the second primary amplifier. The output terminals of the first primary amplifier and the second primary amplifier are respectively connected to the positive and negative input terminals of the signal processing module. The positive and negative output terminals of the signal processing module are respectively connected to the positive and negative input terminals of the current common amplifier. The signal processing module adjusts the output signals of the first primary amplifier and the second primary amplifier into target differential signals with equal amplitude and opposite phase, and outputs the target differential signals to the current common amplifier. The positive feedback resistor and the positive feedback capacitor are both connected in parallel between the positive input terminal and the negative output terminal of the current-shared amplifier, and the negative feedback resistor and the negative feedback capacitor are both connected in parallel between the negative input terminal and the positive output terminal of the current-shared amplifier. The signal processing module includes a signal multiplier, which is used for: The difference signal is obtained by subtracting the output signal of the second primary amplifier from the output signal of the first primary amplifier. The difference signal is inverted to obtain an inverted difference signal, and the difference signal and the inverted difference signal constitute the target difference signal; The difference signal is output from the positive output terminal of the signal processing module, and the inverted difference signal is output from the negative output terminal of the signal processing module.

2. The single-ended to differential microphone circuit according to claim 1, characterized in that, The signal multiplier includes four switched capacitors, each of which includes two first switches, two second switches, and a capacitor. The four switched capacitors are respectively a first switched capacitor, a second switched capacitor, a third switched capacitor, and a fourth switched capacitor. Wherein, the positive terminal of the first switched capacitor is connected to the positive input terminal of the signal processing module through a first switch and to the positive output terminal of the signal processing module through a second switch; the negative terminal of the capacitor is connected to the negative input terminal of the signal processing module through another first switch and to the input common-mode voltage through another second switch. The positive terminal of the second switched capacitor is connected to the positive input terminal of the signal processing module through one of the first switches and to the input common-mode voltage through one of the second switches. The negative terminal of the capacitor is connected to the negative input terminal of the signal processing module through another of the first switches and to the negative output terminal of the signal processing module through another of the second switches. The positive terminal of the third switched capacitor is connected to the positive output terminal of the signal processing module through a first switch and to the positive input terminal of the signal processing module through a second switch. The negative terminal of the capacitor is connected to the input common-mode voltage through another first switch and to the negative input terminal of the signal processing module through another second switch. The positive terminal of the fourth switched capacitor is connected to the input common-mode voltage through a first switch and to the positive input terminal of the signal processing module through a second switch. The negative terminal of the capacitor is connected to the negative output terminal of the signal processing module through another first switch and to the negative input terminal of the signal processing module through another second switch. All the first and second switches are controlled by a set clock signal: when the clock signal is in the first phase, all the first switches are closed and all the second switches are open; when the clock signal is in the second phase opposite to the first phase, all the first switches are open and all the second switches are closed.

3. The single-ended to differential microphone circuit according to claim 1, characterized in that, The single-ended to differential microphone circuit also includes a first chopper switch and a second chopper switch. The first chopper switch is connected in series between the output terminal of the microphone and the input terminal of the first primary amplifier through one input terminal and one output terminal, and the first chopper switch is connected in series between the negative terminal of the coupling capacitor and the input terminal of the second primary amplifier through another input terminal and another output terminal. The second chopper switch is connected in series between the output of the first primary amplifier and the positive input of the signal processing module through one input terminal and one output terminal, and the second chopper switch is connected in series between the output of the second primary amplifier and the negative input of the signal processing module through another input terminal and another output terminal.

4. The single-ended to differential microphone circuit according to claim 1, characterized in that, The current-shared amplifier includes a bias current source, a first PMOS transistor, a second PMOS transistor, a first NMOS transistor, a second NMOS transistor, a third NMOS transistor, and a fourth NMOS transistor; The source of the first PMOS transistor and the source of the second PMOS transistor are both connected to the output terminal of the bias current source. The gate of the first PMOS transistor is connected to the gate of the first NMOS transistor and together serve as the positive input terminal of the current-shared amplifier. The drain of the first PMOS transistor is connected to the drain of the first NMOS transistor and the gate of the third NMOS transistor and together serve as the negative output terminal of the current-shared amplifier. The gate of the second PMOS transistor is connected to the gate of the second NMOS transistor and together serve as the negative input terminal of the current-shared amplifier. The drain of the second PMOS transistor is connected to the drain of the second NMOS transistor and the gate of the fourth NMOS transistor and together serve as the positive output terminal of the current-shared amplifier. The source of the first NMOS transistor is connected to the drain of the third NMOS transistor, the source of the second NMOS transistor, and the drain of the fourth NMOS transistor. The source of the third NMOS transistor and the source of the fourth NMOS transistor are both grounded.

5. The single-ended to differential microphone circuit according to claim 1, characterized in that, The single-ended to differential microphone circuit also includes a second bias resistor and a third bias resistor; One end of the second bias resistor is connected to the input terminal of the first primary amplifier, and the other end of the second bias resistor is used to input the second bias voltage; One end of the third bias resistor is connected to the input terminal of the second primary amplifier, and the other end of the third bias resistor is used to input the second bias voltage.

6. The single-ended to differential microphone circuit according to claim 5, characterized in that, The first bias voltage is greater than the second bias voltage.

7. The single-ended to differential microphone circuit according to claim 6, characterized in that, The resistance value of the first bias resistor ranges from 100GΩ to 200GΩ.

8. The single-ended to differential microphone circuit according to claim 1, characterized in that, The positive feedback resistor and the negative feedback resistor have the same resistance value, and the positive feedback capacitor and the negative feedback capacitor have the same capacitance value.

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