Microphone amplifier circuit, microphone circuit, and electronic device

Abstract

The embodiments of the present invention provide a microphone amplifier circuit, a microphone circuit, and an electronic device. The microphone amplifier circuit comprises a first transistor, a first constant-current source, and a source follower. A gate electrode of the first transistor serves as an input end of the microphone amplifier circuit, a source electrode of the first transistor serves as an output end of the microphone amplifier circuit, and a drain electrode of the first transistor is grounded. An input end of the first constant-current source is connected to a power supply, and an output end of the first constant-current source is connected to the source electrode of the first transistor. The source follower at least comprises a second transistor. A drain electrode of the second transistor is connected to the power supply, a gate electrode of the second transistor is connected to the source electrode of the first transistor, and a source electrode of the second transistor is connected to the drain electrode of the first transistor. The present invention at least facilitates an improvement to the THD performance of microphone amplifier circuits.

Description

Microphone amplifier circuit, microphone circuit and electronic device Technical Field

[0001] The present invention relates to the technical field of microphones, and in particular to a microphone amplifier circuit, a microphone circuit and an electronic device. Background Art

[0002] With the development of mobile communication technology, mobile phones, smart speakers, laptops, etc. have become common electronic products in our lives. The microphone circuits installed in these electronic products usually include a microphone body and a microphone amplifier circuit. The microphone serves as a sound pickup unit, which is used to convert the sound signal into an electrical signal. The microphone amplifier circuit is used to drive the signal output by the microphone to be output to subsequent devices. Technical issues

[0003] Total harmonic distortion (THD) is an important indicator for evaluating microphone performance. THD refers to the ratio of the effective value of the output signal generated by harmonic distortion to the effective value of the total output signal. The THD performance of current microphone amplifier circuits needs to be improved. Technical Solutions

[0004] Embodiments of the present invention provide a microphone amplifier circuit, a microphone circuit, and an electronic device, which are at least beneficial for improving the THD performance of the microphone amplifier circuit.

[0005] On the one hand, an embodiment of the present invention provides a microphone amplifier circuit, comprising: a first transistor, a first constant current source and a source follower. The gate of the first transistor serves as the input end of the amplifier circuit, the source of the first transistor serves as the output end of the amplifier circuit, and the drain of the first transistor is grounded. The gate of the first transistor serves as the input end of the microphone amplifier circuit, the source of the first transistor serves as the output end of the microphone amplifier circuit, and the drain of the first transistor is grounded. The input end of the first constant current source is connected to a power supply, and the output end of the first constant current source is connected to the source of the first transistor. The source follower includes at least a second transistor, the drain of the second transistor is connected to the power supply, the source of the second transistor is connected to the drain of the first transistor, and the gate of the second transistor is connected to the source of the first transistor.

[0006] In some embodiments, the microphone amplifying circuit further includes a second constant current source, an input end of the second constant current source is connected to a power supply, and an output end of the second constant current source is connected to a drain of the second transistor.

[0007] In some embodiments, the microphone amplification circuit further includes a third transistor, a source of the third transistor is connected to the power supply, a gate of the third transistor is connected to the drain of the second transistor, and a drain of the third transistor is connected to the source of the first transistor.

[0008] In some embodiments, the third transistor is a P-channel metal oxide semiconductor (PMOS) transistor.

[0009] In some embodiments, the microphone amplifier circuit further includes a bias branch for providing a bias current to the first transistor and the second transistor.

[0010] In some embodiments, the bias branch includes: a bias transistor, a resistor, a third constant current source, and a fourth transistor. The bias transistor has a gate, a source, and a drain connected to the drain of the first transistor. The first end of the resistor is connected to the source of the bias transistor, and the second end of the resistor is grounded. The input end of the third constant current source is connected to a power supply, and the output end of the third constant current source is connected to the gate of the bias transistor. The source of the fourth transistor is grounded, the gate of the fourth transistor is connected to the source of the bias transistor, and the drain of the fourth transistor is connected to the gate of the bias transistor.

[0011] In some embodiments, the bias transistor and the fourth transistor are N-channel metal oxide semiconductor (NMOS) transistors.

[0012] In some embodiments, the first transistor is a PMOS transistor, and the second transistor and the bias transistor are both NMOS transistors.

[0013] Another embodiment of the present invention provides a microphone circuit, comprising: a microphone and a microphone amplifier circuit as described in any one of the above embodiments. A first end of the microphone is connected to a microphone bias voltage, and a second end of the microphone is connected to an input end of the microphone amplifier circuit.

[0014] Another aspect of the present invention provides an electronic device, including: the microphone amplifier circuit as described in any one of the above embodiments, or including the microphone circuit as described in any one of the above embodiments.

[0015] In an embodiment of the present invention, by optimizing the microphone amplifier circuit, it is ensured that the voltage across the parasitic capacitance Cgd from the gate to the drain of the first transistor in the microphone amplifier circuit is constant, or that the voltage across the parasitic capacitance Cgd from the gate to the drain of the first transistor in the microphone amplifier circuit changes very little, thereby ensuring that there is no charge change or very little charge change in the parasitic capacitance, reducing the input capacitance of the microphone amplifier circuit, thereby effectively weakening or even eliminating the load effect of the parasitic capacitance Cgd from the gate to the drain of the first transistor, and improving the THD performance of the microphone amplifier circuit. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Embodiments of the invention are described by way of example and not limitation with reference to the accompanying drawings in which like references indicate similar elements.

[0017] FIG1 is a schematic diagram of a circuit structure of a microphone amplifier circuit provided by the related art.

[0018] FIG2 is a schematic diagram of the circuit structure of a microphone amplifier circuit provided by an embodiment of the present invention.

[0019] FIG3 is a schematic diagram of the circuit structure of another microphone amplifier circuit provided by an embodiment of the present invention.

[0020] FIG4 is a schematic diagram of the circuit structure of a microphone circuit provided by an embodiment of the present invention. Modes for Carrying Out the Invention

[0021] As known from the background art, the THD performance of current microphone amplifier circuits needs to be improved.

[0022] Figure 1 is a schematic diagram of the circuit structure of a microphone amplifier circuit provided by the related art. Referring to Figure 1 , the input terminal IN0 of amplifier circuit 10 is used to receive a signal output by an external microphone. Amplifier circuit 10 amplifies the signal and outputs it through output terminal OUT0. Microphone amplifier circuit 10 includes a constant current source I0 and a transistor M. The gate of transistor M serves as the input terminal IN0 of microphone amplifier circuit 10, the source of transistor M serves as the output terminal OUT0 of microphone amplifier circuit 10, and the drain of transistor M is grounded. The input terminal of constant current source I0 is connected to power supply VDD, and the output terminal of constant current source I0 is connected to the source of transistor M.

[0023] The external microphone may be a microelectromechanical system (MEMS) sensor. When a standalone MEMS sensor has no capacitive load, the total harmonic distortion (THD) of a standalone MEMS sensor can be as high as 1%. In the amplifier circuit 10 shown in Figure 1, the parasitic capacitance Cgd0 between the gate and drain of transistor M increases the input capacitance of amplifier circuit 10. For a standalone amplifier, if the input signal has strong drive capability, Cgd0 has little impact on the amplifier's 1% THD. The problem lies in the high impedance of the MEMS sensor at the MEMS output and its weak drive capability. When the MEMS sensor is connected to the amplifier, the parasitic capacitance Cgd0 acts as a capacitive load. In this case, the parasitic capacitance Cgd0 significantly reduces the 1% THD of the entire MEMS and amplifier system. The loading effect of the parasitic capacitance Cgd0 results in poor total harmonic distortion (THD) performance of the amplifier circuit, which in turn causes audio distortion in the output of smart mobile devices using this amplifier circuit.

[0024] To address the above-mentioned issues, in an embodiment of the present invention, the amplifier circuit is optimized to ensure that the voltage across the parasitic capacitor Cgd between the gate and drain of the transistor in the amplifier circuit is constant, or to ensure that the voltage across the parasitic capacitor Cgd between the gate and drain of the transistor changes very little. This ensures that the charge of the parasitic capacitor Cgd changes very little or not, thereby reducing the capacitive load of the MEMS sensor, thereby effectively weakening or even eliminating the capacitive load effect of the parasitic capacitor Cgd, and improving the THD performance of the entire system including the MEMS sensor and the amplifier circuit.

[0025] The following describes various embodiments of the present invention in detail with reference to the accompanying drawings. However, those skilled in the art will appreciate that many technical details are provided in the various embodiments of the present invention to facilitate a better understanding of the embodiments of the present invention. However, even without these technical details and the various variations and modifications based on the following embodiments, the technical solutions claimed in the embodiments of the present invention can still be implemented.

[0026] FIG2 is a schematic diagram of the circuit structure of a microphone amplifier circuit provided by an embodiment of the present invention.

[0027] 2 , the amplifier circuit 200 is configured to receive a sound pressure signal output by an external microphone through an input terminal IN, amplify the sound pressure signal, and output the amplified signal through an output terminal OUT.

[0028] The amplifier circuit 200 includes a first transistor M1 and a first constant current source I1. The gate of the first transistor M1 serves as the input terminal IN of the microphone amplifier circuit 100, the source of the first transistor M1 serves as the output terminal OUT of the microphone amplifier circuit 100, and the drain of the first transistor M1 is grounded GND. The input terminal of the first constant current source I1 is connected to the power supply VDD, and the output terminal of the first constant current source I1 is connected to the source of the first transistor M1.

[0029] The amplifier circuit 200 also includes a source follower. The source follower includes at least a second transistor M2. The gate of the second transistor M2 is connected to the source of the first transistor M1, the source of the second transistor M2 is connected to the drain of the first transistor M1, and the drain of the second transistor M2 is connected to the power supply VDD. The second transistor M2, as a source follower, keeps the voltage Vgd between the gate and drain of the first transistor M1 constant. In other words, there is no charge change on the parasitic capacitance Cgd between the gate and drain of the first transistor M1. Therefore, the capacitive load effect of Cgd on the previous MEMS sensor is offset, and the input capacitance of the application specific integrated circuit (ASIC) is very small. As a result, the THD performance of the entire system, including the MEMS sensor and the amplifier circuit, is improved by 1%.

[0030] In some embodiments, the source follower further includes a second constant current source I2. In this case, the drain of the second transistor M2 is connected to the power supply VDD through the second constant current source I2. Specifically, the input of the second constant current source I2 is connected to the power supply VDD, and the output of the second constant current source I2 is connected to the drain of the second transistor M2. The second constant current source I2 and the second transistor M2 form a source follower, which is used to eliminate the loading effect of the parasitic capacitance Cgd on the preceding MEMS sensor.

[0031] The second constant current source I2 is used to provide a constant current to the second transistor M2, so that the voltage VGS2 between the gate and source of the second transistor M2 remains constant, thereby maintaining the voltage VGS1 between the gate and source of the first transistor M1 constant. In this way, the voltage VGD1 between the gate and drain of the first transistor M1 also remains constant, that is, the voltage across the parasitic capacitor Cgd between the gate and drain of the first transistor M1 remains constant. Alternatively, the second constant current source I2 is used to provide a constant current to the second transistor M2, so that the voltage VGS2 between the gate and source of the second transistor M2 changes less, thereby maintaining the voltage VGS1 between the gate and source of the first transistor M1 changes less. In this way, the voltage VGD1 between the gate and drain of the first transistor M1 changes less, that is, the voltage across the parasitic capacitor Cgd between the gate and drain of the first transistor M1 changes less.

[0032] In this way, by providing the second transistor M2, the voltage across the parasitic capacitor Cgd from the gate to the drain of the first transistor M1 is kept constant, or the change in the voltage across the parasitic capacitor Cgd from the gate to the drain of the first transistor M1 is kept small, thereby ensuring that the parasitic capacitor Cgd has no charge change or very little charge change, thereby effectively weakening or even eliminating the capacitive load effect of the parasitic capacitor Cgd from the gate to the drain of the first transistor M1 on the front-stage MEMS sensor, thereby improving the THD performance of the entire system including the MEMS sensor and the microphone amplifier circuit 200.

[0033] In some embodiments, the first transistor M1 is a PMOS transistor, and the second transistor M2 is an NMOS transistor.

[0034] In some embodiments, the amplifier circuit 200 further includes a third transistor M3. The gate of the third transistor M3 is connected to the drain of the second transistor M2, the source of the third transistor M3 is connected to the power supply VDD, and the drain of the third transistor M3 is connected to the source of the first transistor M1. The voltage VSG3 between the source and gate of the third transistor M3 is used to define the voltage between the two terminals of the second constant current source I2. The third transistor M3 also provides an output current from the power supply VDD to the load circuit of the amplifier circuit 200 via the third transistor M3 and the output terminal. The first transistor M1 provides a current from the load circuit of the amplifier circuit 200 to the source of the first transistor M1 via the output terminal. The first transistor M1 and the third transistor M3 form a push-pull drive circuit.

[0035] In some embodiments, the third transistor M3 is a PMOS transistor.

[0036] In some embodiments, the amplifier circuit 200 further includes a bias branch for providing a bias current source (sink) to the first transistor M1 and the second transistor M2 .

[0037] In some embodiments, the bias branch includes a bias transistor M0, a resistor R, a third constant current source I3, and a fourth transistor M4. The drain of the bias transistor M0 is connected to the drain of the first transistor M1. The first end of the resistor R is connected to the source of the bias transistor M0, and the second end of the resistor R is grounded GND. The input end of the third constant current source I3 is connected to the power supply VDD, and the output end of the third constant current source I3 is connected to the gate of the bias transistor M0. The gate of the fourth transistor M4 is connected to the source of the bias transistor M0, the drain of the fourth transistor M4 is connected to the gate of the bias transistor M0, and the source of the fourth transistor M4 is grounded GND. In this case, the bias transistor M0, the resistor R, the third constant current source I3, and the fourth transistor M4 together provide a bias current for the first transistor M1 and the second transistor M2. Since the current sink bias circuit including the third constant current source I3, the fourth transistor M4, the resistor R and the bias transistor M0 provides a constant current source (current sink) for the drain of the first transistor M1 and the source of the second transistor M2, the channel current of the first transistor M1 is constant. Therefore, the voltage VGS1 between the gate and the source of the first transistor M1 is constant, thereby making the voltage VGD1 between the gate and the drain of the first transistor M1 constant, that is, the voltage on the parasitic capacitor Cgd is constant.

[0038] In some embodiments, the bias transistor M0 and the fourth transistor M4 are NMOS transistors.

[0039] In some other embodiments, a constant current source may be used to provide bias current for the first transistor M1 and the second transistor M2. Specifically, as shown in FIG3 , the bias branch includes another constant current source I4, one terminal of which is connected to the drain of the first transistor M1 and the other terminal is grounded GND.

[0040] The amplifier circuit provided in the above embodiment, through circuit improvement, ensures that the voltage across the parasitic capacitor Cgd from the gate to the drain of the first transistor in the amplifier circuit is a constant value, or ensures that the voltage across the parasitic capacitor Cgd from the gate to the drain of the first transistor changes very little, thereby ensuring that the parasitic capacitor Cgd has no charge change or very little charge change, thereby effectively reducing or even eliminating the capacitive load effect of the parasitic capacitor Cgd on the MEMS sensor, and improving the THD performance of the entire system including the MEMS sensor and the microphone amplifier circuit.

[0041] FIG4 is a schematic diagram of the circuit structure of a microphone circuit provided by an embodiment of the present invention.

[0042] 4 , the microphone circuit includes a microphone Mic and an amplifier circuit 200 as in any one of the above embodiments. A first terminal of the microphone Mic is connected to a microphone bias voltage Vcp, and a second terminal of the microphone is connected to an input terminal IN of the microphone amplifier circuit 200 .

[0043] Another aspect of the present invention provides an electronic device, including: the microphone amplifier circuit as described in any one of the above embodiments, or including the microphone circuit as described in any one of the above embodiments.

[0044] It should be understood that although the terms first, second, etc. are used in some cases herein to describe various components, these components should not be limited by these terms. These terms are only used to distinguish one component from another. For example, a first transistor can be referred to as a second transistor, and similarly, a second transistor can be referred to as a first transistor without departing from the scope of the various embodiments described. The first constant current source and the second constant current source are both constant current sources, but their parameters are not the same unless explicitly stated.

[0045] Throughout this specification, when a component is referred to as "including" another component, unless otherwise specified, this does not exclude other components, and other components may also be included. In addition, when a component such as a transistor is referred to as being "connected" to another component, it may be "directly connected" to the other component or another component may be present therebetween. Furthermore, when a component is "directly connected" to another component, this means that no other components are present therebetween.

[0046] The terms used in the description of the various described embodiments herein are intended only to describe specific embodiments and are not intended to be limiting. As used in the description of the various described embodiments and in the appended claims, the singular forms "a," "an," and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that the term "and / or" as used herein is intended to encompass any and all possible combinations of one or more of the associated listed items. It should be further understood that the terms "includes," "including," "comprises," and / or "comprising" as used herein specify the presence of stated features, ingredients, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, ingredients, steps, operations, elements, components, and / or groups thereof.

[0047] For ease of explanation, the above description has been described with reference to specific embodiments. However, the above illustrative discussion is not exhaustive and is not intended to limit the scope of the claims to the precise forms disclosed. In light of the above teachings, many modifications and variations are possible. These embodiments have been selected to best explain the basic principles of the claims and their practical application, thereby enabling others skilled in the art to best use these embodiments and make various modifications as appropriate to the specific application contemplated. The scope of protection of the present invention should be based on the scope defined by the claims.

Claims

1. A microphone amplification circuit, characterized in that, Comprising: A first transistor having a gate as an input terminal of the microphone amplifier circuit, a source as an output terminal of the microphone amplifier circuit, and a drain grounded; A first constant current source having an input terminal connected to a power supply and an output terminal connected to the source of the first transistor; And A source follower including at least a second transistor having a drain connected to the power supply, a gate to the source of the first transistor, and a source connected to the drain of the first transistor.

2. The microphone amplification circuit according to claim 1, characterized in that, The source follower further comprises: A second constant current source having an input terminal connected to the power supply and an output terminal connected to the drain of the second transistor.

3. The microphone amplification circuit according to claim 2, characterized in that, The microphone amplifier circuit further comprises a third transistor having a gate to the drain of the second transistor, a source connected to the power supply, and a drain connected to the source of the first transistor.

4. The microphone amplification circuit according to claim 3, wherein The third transistor is a P-channel metal oxide semiconductor transistor.

5. The microphone amplification circuit according to claim 1, characterized in that The microphone amplifier circuit further comprises a bias branch for providing a bias current to the first transistor and the second transistor.

6. The microphone amplification circuit according to claim 5, characterized in that, The bias branch comprises: A bias transistor having a gate, a source, and a drain connected to the drain of the first transistor; A resistor having a first end connected to the source of the bias transistor and a second end grounded; A third constant current source having an input terminal connected to the power supply and an output terminal connected to the gate of the bias transistor; A fourth transistor having a gate connected to the source of the bias transistor, a drain connected to the gate of the bias transistor, and a source grounded.

7. The microphone amplification circuit according to claim 6, wherein The bias transistor and the fourth transistor are N-channel metal oxide semiconductor transistors.

8. The microphone amplification circuit according to claim 5, wherein The bias branch comprises a fourth constant current source having one end connected to the drain of the first transistor and the other end grounded.

9. The microphone amplification circuit according to claim 1, characterized in that, The first transistor is a P-channel metal oxide semiconductor transistor and the second transistor is an N-channel metal oxide semiconductor transistor.

10. A microphone circuit, characterized in that, Comprising: The microphone amplifier circuit according to any one of claims 1 to 9, and A microphone having a first end connected to a microphone bias voltage and a second end connected to the input terminal of the microphone amplifier circuit.

11. An electronic device, characterized in that, Comprising: The microphone amplifier circuit according to any one of claims 1 to 9, or comprising the microphone circuit according to claim 10.

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