CN108768317B - MEMS microphone preamplifier - Google Patents
MEMS microphone preamplifier Download PDFInfo
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- CN108768317B CN108768317B CN201810999794.5A CN201810999794A CN108768317B CN 108768317 B CN108768317 B CN 108768317B CN 201810999794 A CN201810999794 A CN 201810999794A CN 108768317 B CN108768317 B CN 108768317B
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- amplifier
- demodulation circuit
- mems microphone
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- 239000003990 capacitor Substances 0.000 claims abstract description 68
- 230000010355 oscillation Effects 0.000 claims description 6
- 238000010586 diagram Methods 0.000 description 6
- 239000002184 metal Substances 0.000 description 3
- 229910052751 metal Inorganic materials 0.000 description 3
- 230000000694 effects Effects 0.000 description 2
- 230000005764 inhibitory process Effects 0.000 description 2
- 239000000758 substrate Substances 0.000 description 2
- 230000005684 electric field Effects 0.000 description 1
- 230000005669 field effect Effects 0.000 description 1
- 238000001914 filtration Methods 0.000 description 1
- PCHJSUWPFVWCPO-UHFFFAOYSA-N gold Chemical compound [Au] PCHJSUWPFVWCPO-UHFFFAOYSA-N 0.000 description 1
- 239000010931 gold Substances 0.000 description 1
- 229910052737 gold Inorganic materials 0.000 description 1
- 230000036039 immunity Effects 0.000 description 1
- 238000000034 method Methods 0.000 description 1
- 239000002985 plastic film Substances 0.000 description 1
- 229920006255 plastic film Polymers 0.000 description 1
- 230000000750 progressive effect Effects 0.000 description 1
- 230000035945 sensitivity Effects 0.000 description 1
- 230000000087 stabilizing effect Effects 0.000 description 1
Classifications
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03F—AMPLIFIERS
- H03F3/00—Amplifiers with only discharge tubes or only semiconductor devices as amplifying elements
- H03F3/181—Low frequency amplifiers, e.g. audio preamplifiers
- H03F3/183—Low frequency amplifiers, e.g. audio preamplifiers with semiconductor devices only
- H03F3/187—Low frequency amplifiers, e.g. audio preamplifiers with semiconductor devices only in integrated circuits
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03F—AMPLIFIERS
- H03F1/00—Details of amplifiers with only discharge tubes, only semiconductor devices or only unspecified devices as amplifying elements
- H03F1/26—Modifications of amplifiers to reduce influence of noise generated by amplifying elements
-
- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03F—AMPLIFIERS
- H03F1/00—Details of amplifiers with only discharge tubes, only semiconductor devices or only unspecified devices as amplifying elements
- H03F1/30—Modifications of amplifiers to reduce influence of variations of temperature or supply voltage or other physical parameters
Abstract
The invention discloses a MEMS microphone pre-amplifier, comprising: the frequency demodulation circuit comprises a first capacitor, a first resistor, a frequency demodulation circuit and an output buffer, wherein the first resistor and the first capacitor form an RC oscillator, one input end of the frequency demodulation circuit is connected with one end of the first capacitor, the other end of the first capacitor is grounded, the other input end of the frequency demodulation circuit is connected with one end of the first resistor, the other end of the first resistor is grounded, and the output end of the frequency demodulation circuit is connected with the input end of the output buffer. The amplifier provided by the invention does not need a DC-DC booster circuit to generate high voltage, does not need an MEMS sensor to be connected to one bias voltage through a large bias resistor, has low cost and small noise, and can also improve the power supply voltage rejection ratio (PSRR).
Description
Technical Field
The invention relates to the field, in particular to a MEMS microphone preamplifier.
Background
The principle of microphone operation is that the sound pressure causes the capacitance change of the capacitance sensor, the traditional resident body microphone injects the charge into one electrode plate of the microphone (the electrode plate is a very thin plastic film, one side of the electrode plate is evaporated with a layer of metal film, then after the high voltage electric field is resident, the opposite charges are respectively resident on the two sides of the electrode plate, the evaporated gold surface of the film is outwards communicated with the metal shell), the charges can not flow, when the sound pressure causes the resident body capacitance change, the voltage on the electrode plate changes, and the voltage signal is read out by a Junction Field Effect Transistor (JFET) amplifier. The MEMS sensor microphone is a metal electrode plate on which charges cannot be fixed and do not flow. The MEMS sensor has one substrate connected to a fixed voltage and the other substrate connected to a preamplifier. As shown in fig. 1, in order to improve sensitivity, the MEMS sensor needs to be connected to a bias voltage of around 10V. This requires that the MEMS sensor pre-amplifier include an additional DC-DC booster to generate a voltage of around 10V from around 1.8V power supply, biasing the MEMS sensor through a large resistor R1. When the acoustic pressure causes a change in the capacitance of the MEMS sensor, the MEMS sensor has substantially no change in the charge on the capacitance of the MEMS sensor due to the large series resistance (r1+r2), and the acoustic pressure causes a change in the voltage signal on the MEMS sensor.
The pre-amplifier of the MEMS sensor has the following problems that a DC-DC booster circuit occupies a large area and the chip cost is high; the DC-DC booster circuit needs an oscillator, and the generated high bias voltage source has high noise; the DC-DC booster requires a certain time to generate a large bias voltage, and the microphone is slow to start; DC-DC booster noise is directly coupled to the input, the signal-to-noise ratio (SNR) becomes low, and the immunity to power supply ripple interference may become poor; meanwhile, the MEMS requires a large bias resistor, the sound pressure is large, the voltage signal is changed greatly, the bias resistor is reduced or nonlinear, and an advanced harmonic interference signal or frequency response is poor.
Disclosure of Invention
The invention aims to provide a MEMS microphone preamplifier which has the advantages of low cost, low noise and high power supply voltage inhibition ratio.
In order to achieve the above object, the present invention provides the following solutions:
a MEMS microphone pre-amplifier comprising: the frequency demodulation circuit comprises a first capacitor, a first resistor, a frequency demodulation circuit and an output buffer, wherein the first resistor and the first capacitor form an RC oscillator, one input end of the frequency demodulation circuit is connected with one end of the first capacitor, the other end of the first capacitor is grounded, the other input end of the frequency demodulation circuit is connected with one end of the first resistor, the other end of the first resistor is grounded, and the output end of the frequency demodulation circuit is connected with the input end of the output buffer.
Optionally, the frequency demodulation circuit includes: an amplifier, a low pass filter, a voltage controlled oscillator and a divider;
one input end of the amplifier is connected with one end of the first capacitor, the other input end of the amplifier is connected with one end of the first resistor, and the output end of the amplifier is sequentially connected with a voltage-controlled oscillator and a divider; the low-pass filter is connected between the amplifier and the voltage-controlled oscillator, and the output buffer is connected with the low-pass filter.
Optionally, the low-pass filter includes a second resistor, a second capacitor, and a third capacitor; one end of the second resistor is connected with the output end of the amplifier, the other end of the second resistor is connected with one end of the second capacitor, the other end of the second capacitor is grounded, one end of the third capacitor is connected with the output end of the amplifier, the other end of the third capacitor is grounded, and the output buffer is connected with the other end of the second resistor.
Optionally, the MEMS microphone pre-amplifier further comprises: the device comprises a fourth capacitor, a first current source and a second current source, wherein one end of the first current source is connected with one end of the second current source, the other end of the first current source is connected with one end of the fourth capacitor, the other end of the fourth capacitor is grounded, and the other end of the second current source is connected with one end of the first resistor.
Optionally, the MEMS microphone pre-amplifier further comprises: the device comprises a fifth capacitor, a third resistor and a fourth resistor, wherein one end of the third resistor is connected with one end of the fourth resistor, the other end of the third resistor is connected with one end of the fifth capacitor, the other end of the fifth capacitor is grounded, and the other end of the fourth resistor is connected with one end of the first resistor.
Optionally, the MEMS microphone pre-amplifier further comprises: a first switch, a second switch, a first inverter, and a second inverter;
the first switch is connected in series with the second switch and then connected in parallel with the fourth capacitor, one end of the first capacitor is connected to a connecting wire of the first switch and the second switch, and the other end of the first capacitor is grounded;
the input end of the first inverter is connected with the output end of the divider, the first inverter is connected with the second inverter in series, the output end of the second inverter controls the opening and closing of the second switch, and the output end of the first inverter controls the opening and closing of the first switch.
Optionally, the first capacitance is a MEMS capacitor.
Optionally, the RC oscillator is a relaxation oscillator, and the oscillation frequency is 0.1-10MHz.
Optionally, the resistance value of the first resistor is 160kΩ -200kΩ.
According to the specific embodiment provided by the invention, the invention discloses the following technical effects:
the invention uses MEMS sensor capacitance and resistance to form an oscillator, uses a Frequency Locking Loop (FLL) as a frequency modulation demodulation circuit to demodulate a voltage signal, and the voltage signal corresponds to the MEMS sensor capacitance change caused by sound pressure change, thereby causing the oscillator frequency change. The amplifier provided by the invention does not need a DC-DC booster circuit to generate high voltage, does not need an MEMS sensor to be connected to one bias voltage through a large bias resistor, has low cost and small noise, and can also improve the power supply voltage rejection ratio (PSRR).
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings that are needed in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.
FIG. 1 is a conventional MEMS microphone sensor preamplifier;
FIG. 2 is a structural connection diagram of an embodiment 1 of the MEMS microphone preamplifier of the invention;
FIG. 3 is a structural connection diagram of embodiment 2 of the MEMS microphone preamplifier of the invention;
fig. 4 is a structural connection diagram of embodiment 3 of the MEMS microphone pre-amplifier of the invention.
Detailed Description
The following description of the embodiments of the present invention will be made clearly and completely with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
The invention aims to provide a MEMS microphone preamplifier which has the advantages of low cost, low noise and high power supply voltage inhibition ratio.
In order that the above-recited objects, features and advantages of the present invention will become more readily apparent, a more particular description of the invention will be rendered by reference to the appended drawings and appended detailed description.
Example 1
Fig. 2 is a structural connection diagram of an embodiment 1 of the MEMS microphone pre-amplifier of the present invention. As shown in fig. 2, the MEMS microphone pre-amplifier includes: the frequency demodulation circuit comprises an adjustable capacitor C1, a resistor R1, a frequency demodulation circuit (FLL) and an output buffer, wherein the MEMS is used as the adjustable capacitor C1 and the resistor R1 to form an RC oscillator, one input end of the frequency demodulation circuit (FLL) is connected with one end of the adjustable capacitor C1, the other end of the adjustable capacitor C1 is grounded, the other input end of the frequency demodulation circuit is connected with one end of the resistor R1, the other end of the resistor R1 is grounded, and the output end of the frequency demodulation circuit is connected with the output buffer.
According to the principle of a relaxation oscillator (Relaxation Oscillator), the relaxation oscillator is formed by utilizing the capacitance of the MEMS sensor and the internal resistance of a preamplifier, the oscillation frequency of the relaxation oscillator does not change along with the power supply voltage VCC, the oscillation frequency is only determined by the RC constants of a resistor R1 and a capacitor C1, the capacitance of the MEMS sensor is about 1pF, and when the capacitance of the MEMS sensor is changed due to sound pressure, the oscillation frequency of the relaxation oscillator is changed. The resistor with the resistance value of 160KΩ -200KΩ can be selected to make the relaxation oscillator oscillate in the range of 0.1-10MHz, and if the relaxation oscillator can oscillate in the range of 1-5MHz, the effect is better. The pre-amplifier provided by the invention further comprises a frequency locking circuit (FLL), wherein the oscillation signal of the relaxation oscillator can be input into the FLL as a reference clock signal, the FLL adjusts the frequency of a loop oscillator (RING-VCO) of the relaxation oscillator and follows the frequency change of the relaxation oscillator, so that the loop oscillator control voltage also adjusts the loop oscillator along with the frequency change of the relaxation oscillator, the loop oscillator control voltage signal is consistent with the sound pressure signal, and the loop oscillator control signal demodulated by the FLL is the corresponding sound pressure signal. The signal may be output through a first stage buffer amplifier.
The MEMS sensor is used as a capacitor (about 1 pF) C1, the capacitor C1 and the resistor R1 constitute a relaxation oscillator, the frequency variation of the relaxation oscillator is demodulated by an internal frequency demodulation circuit (FLL) on the preamplifier, the capacitance variation of the capacitor C1 causes the frequency variation, the frequency demodulation circuit (FLL) demodulates the frequency variation to the voltage signal, and thereby the sound pressure signal is read out. Compared with the traditional MEMS sensor microphone amplifier, the invention has the advantages that a DC-DC booster circuit is not needed to generate large bias voltage, the chip area is saved, meanwhile, the noise generated by the DC-DC circuit is avoided, a large bias resistor is not needed, and meanwhile, the frequency of the relaxation oscillator does not change along with the VDD.
Example 2
FIG. 3 is a structural connection diagram of embodiment 2 of the MEMS microphone preamplifier of the invention; as shown in fig. 3, the MEMS microphone pre-amplifier includes:
the adjustable capacitor C1, the resistor R1, the amplifier 23, the low-pass filter, the voltage-controlled oscillator 24, the output buffer 25 and the divider 26, wherein one input end of the amplifier 23 is connected with one end of the capacitor C1, the other input end of the amplifier 23 is connected with one end of the resistor R1, and the output end of the amplifier 23 is sequentially connected with the voltage-controlled oscillator 24 and the divider 26.
The low-pass filter comprises a resistor R31, a capacitor C12 and a capacitor C15; one end of a resistor R31 is connected with the output end of the amplifier 23, the other end of the resistor R31 is connected with one end of a capacitor C12, the other end of the capacitor C12 is grounded, one end of a capacitor C15 is connected with the output end of the amplifier 23, the other end of the capacitor C15 is grounded, and the output buffer 25 is connected with the other end of the resistor R31.
The MEMS microphone pre-amplifier further comprises: capacitor C2, current source I10, current source I11, first switch K1, second switch K2, first inverter 27, and second inverter 28.
One end of the current source I10 is connected with one end of the current source I11, the other end of the current source I10 is connected with one end of the capacitor C2, the other end of the capacitor C2 is grounded, and the other end of the current source I11 is connected with one end of the resistor R1. The current source I10 and the current source I11 have the same size, bias current is provided for R1 and C1 (C2), so that the input voltage of the amplifier works in a normal common-mode voltage (common-mode voltage) range, and the size has no influence on the circuit characteristics. C2 is only used for stabilizing the VC1 voltage and reducing VC1 fluctuation caused by CLK switching.
In addition, the first switch K1 and the second switch K2 are connected in series and then connected in parallel with the capacitor C2, one end of the capacitor C1 is connected to a connecting line between the first switch K1 and the second switch K2, and the other end of the capacitor C1 is grounded.
An input end of the first inverter 27 is connected with an output end of the divider 26, the first inverter 27 is connected in series with the second inverter 28, an output end CLKB of the second inverter 28 controls on and off of the second switch K2, and an output end CLK of the first inverter 26 controls on and off of the first switch K1. CLK and CLKB are inverse voltage signals to each other.
The FLL demodulation circuit outputs a reference frequency signal to the VCO control voltage signal through low-pass filtering, and can filter out high-frequency signals. The output gain of the entire preamplifier can be adjusted by changing the size of the divider in the FLL loop.
Example 3
Fig. 4 is a structural connection diagram of embodiment 3 of the MEMS microphone pre-amplifier of the invention. Unlike example 2, the current sources I10 and I11 are replaced with the resistors R110 and R111.
The frequency f of CLK is determined by the following equation: r110/{ 1/(f×cm1) } =r111/R1
Thus, f= (R111/R1) { 1/(R110C 1) }.
In the present specification, each embodiment is described in a progressive manner, and each embodiment is mainly described in a different point from other embodiments, and identical and similar parts between the embodiments are all enough to refer to each other.
The principles and embodiments of the present invention have been described herein with reference to specific examples, the description of which is intended only to assist in understanding the methods of the present invention and the core ideas thereof; also, it is within the scope of the present invention to be modified by those of ordinary skill in the art in light of the present teachings. In view of the foregoing, this description should not be construed as limiting the invention.
Claims (6)
1. A MEMS microphone pre-amplifier, comprising: the frequency demodulation circuit comprises a first capacitor, a first resistor, a frequency demodulation circuit and an output buffer, wherein the first resistor and the first capacitor form an RC oscillator, one input end of the frequency demodulation circuit is connected with one end of the first capacitor, the other end of the first capacitor is grounded, the other input end of the frequency demodulation circuit is connected with one end of the first resistor, the other end of the first resistor is grounded, and the output end of the frequency demodulation circuit is connected with the input end of the output buffer;
the frequency demodulation circuit includes: an amplifier, a low pass filter, a voltage controlled oscillator and a divider;
one input end of the amplifier is connected with one end of the first capacitor, the other input end of the amplifier is connected with one end of the first resistor, and the output end of the amplifier is sequentially connected with a voltage-controlled oscillator and a divider; the low-pass filter is connected between the amplifier and the voltage-controlled oscillator, and the output buffer is connected with the low-pass filter;
the MEMS microphone pre-amplifier further comprises: the device comprises a fourth capacitor, a first current source and a second current source, wherein one end of the first current source is connected with one end of the second current source, the other end of the first current source is connected with one end of the fourth capacitor, the other end of the fourth capacitor is grounded, and the other end of the second current source is connected with one end of the first resistor;
the MEMS microphone pre-amplifier further comprises: the device comprises a fifth capacitor, a third resistor and a fourth resistor, wherein one end of the third resistor is connected with one end of the fourth resistor, the other end of the third resistor is connected with one end of the fifth capacitor, the other end of the fifth capacitor is grounded, and the other end of the fourth resistor is connected with one end of the first resistor.
2. The MEMS microphone pre-amplifier of claim 1 wherein the low pass filter comprises a second resistor, a second capacitor, and a third capacitor; one end of the second resistor is connected with the output end of the amplifier, the other end of the second resistor is connected with one end of the second capacitor, the other end of the second capacitor is grounded, one end of the third capacitor is connected with the output end of the amplifier, the other end of the third capacitor is grounded, and the output buffer is connected with the other end of the second resistor.
3. The MEMS microphone pre-amplifier of claim 1, wherein the MEMS microphone pre-amplifier further comprises: a first switch, a second switch, a first inverter, and a second inverter;
the first switch is connected in series with the second switch and then connected in parallel with the fourth capacitor, one end of the first capacitor is connected to a connecting wire of the first switch and the second switch, and the other end of the first capacitor is grounded;
the input end of the first inverter is connected with the output end of the divider, the first inverter is connected with the second inverter in series, the output end of the second inverter controls the opening and closing of the second switch, and the output end of the first inverter controls the opening and closing of the first switch.
4. The MEMS microphone pre-amplifier of claim 1, wherein the first capacitance is a MEMS capacitor.
5. The MEMS microphone pre-amplifier of claim 1 wherein the RC oscillator is a relaxation oscillator having an oscillation frequency of 0.1-10MHz.
6. The MEMS microphone pre-amplifier of claim 1 wherein the first resistor has a resistance of 160kΩ -200kΩ.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN201810999794.5A CN108768317B (en) | 2018-08-30 | 2018-08-30 | MEMS microphone preamplifier |
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN201810999794.5A CN108768317B (en) | 2018-08-30 | 2018-08-30 | MEMS microphone preamplifier |
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| Publication Number | Publication Date |
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| CN108768317A CN108768317A (en) | 2018-11-06 |
| CN108768317B true CN108768317B (en) | 2024-02-27 |
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Citations (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN101640829A (en) * | 2008-07-30 | 2010-02-03 | 中国科学院声学研究所 | Digital preamplifier for MEMS microphone |
| CN104406612A (en) * | 2014-11-07 | 2015-03-11 | 无锡纳讯微电子有限公司 | Capacitive sensor interface circuit |
| CN104717591A (en) * | 2013-12-16 | 2015-06-17 | 英飞凌科技股份有限公司 | Circuit assembly and method for processing an input signal, and microphone assembly |
| CN105744452A (en) * | 2014-12-12 | 2016-07-06 | 瑞声声学科技(深圳)有限公司 | Mems microphone circuit |
| CN106658303A (en) * | 2016-12-01 | 2017-05-10 | 北京卓锐微技术有限公司 | Microphone system and amplifying circuit |
| WO2018106514A1 (en) * | 2016-12-05 | 2018-06-14 | Knowles Electronics, Llc | High impedance bias for microphones |
| CN208739086U (en) * | 2018-08-30 | 2019-04-12 | 孙茂友 | MEMS microphone preamplifier |
-
2018
- 2018-08-30 CN CN201810999794.5A patent/CN108768317B/en active Active
Patent Citations (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN101640829A (en) * | 2008-07-30 | 2010-02-03 | 中国科学院声学研究所 | Digital preamplifier for MEMS microphone |
| CN104717591A (en) * | 2013-12-16 | 2015-06-17 | 英飞凌科技股份有限公司 | Circuit assembly and method for processing an input signal, and microphone assembly |
| CN104406612A (en) * | 2014-11-07 | 2015-03-11 | 无锡纳讯微电子有限公司 | Capacitive sensor interface circuit |
| CN105744452A (en) * | 2014-12-12 | 2016-07-06 | 瑞声声学科技(深圳)有限公司 | Mems microphone circuit |
| CN106658303A (en) * | 2016-12-01 | 2017-05-10 | 北京卓锐微技术有限公司 | Microphone system and amplifying circuit |
| WO2018106514A1 (en) * | 2016-12-05 | 2018-06-14 | Knowles Electronics, Llc | High impedance bias for microphones |
| CN208739086U (en) * | 2018-08-30 | 2019-04-12 | 孙茂友 | MEMS microphone preamplifier |
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| CN108768317A (en) | 2018-11-06 |
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