Low-cost precise microphone based on MEMS microphone

Abstract

The invention discloses a low-cost precise microphone based on an MEMS microphone, relates to the technical field of microphones, and adopts the superposition of MEMS microphone signals of multiple channels to reduce the background noise of the microphone. The MEMS microphone comprises an MEMS microphone carrier plate, a preamplifier and an output interface, the MEMS microphone carrier plate comprises a plurality of MEMS microphones connected in parallel and is used for collecting sound signals; the pre-amplifier comprises an IEPE power supply module, a voltage following module, an operational amplification module and a direct current bias module; wherein the operational amplification module comprises a plurality of operational amplifiers which are connected in parallel, input nodes of the operational amplifiers are correspondingly connected with output nodes of the MEMS microphones respectively, and the operational amplifiers are used for amplifying sound signals received by the MEMS microphones; and the output interface is used for outputting an output signal of the pre-amplifier. According to the invention, the outputs of a plurality of unrelated noise sources are connected in parallel, the output noise of the active electronic device is averaged, and finally, the background noise of the overall output is reduced, so that the signal-to-noise ratio is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of microphones, and in particular to a low-cost precision microphone based on a MEMS microphone. Background Art

[0002] Traditional commercial condenser microphones are widely used in multiple high-precision acoustic fields, such as audio recording and medical equipment, due to their high sensitivity and low background noise. However, their high cost limits their application in large-scale and low-cost projects, which has given rise to the need for alternative technologies.

[0003] MEMS microphones are manufactured using photolithography and etching, and have the characteristics of good structural consistency. This is because the photolithography and etching steps can very accurately define the microscopic structure and shape, making the structure of the MEMS microphone stable and of good quality. Therefore, MEMS microphones manufactured using photolithography and etching have the advantages of good amplitude and phase consistency and low discreteness. Such characteristics are suitable for tests that are sensitive to phase, such as sound intensity measurement, sound power, and array measurement. In addition, because MEMS microphones use integrated circuit manufacturing technology and their miniaturized design, their manufacturing cost is relatively low, which makes them very popular in consumer electronics and embedded systems, such as smart phones and wearable devices.

[0004] Typically, the noise level of a MEMS microphone is between 25 and 35 dB(A), with specific values ​​depending on the model and manufacturer. Due to the use of semiconductor processes for mass production, the performance parameters of MEMS microphones are very consistent, and the noise level varies little. This consistency allows MEMS microphones to excel in applications that require high stability and reliability. In addition, MEMS microphones have a compact internal design, good shielding, and strong anti-electromagnetic interference capabilities, further reducing the impact of background noise. Overall, MEMS microphones provide low noise while ensuring high consistency and anti-interference performance, making them an ideal choice for many modern electronic devices.

[0005] However, compared to condenser microphones, the sensitivity of MEMS microphones manufactured by photolithography and etching is relatively low. This is because the components such as sensors, circuits, and signal processors in MEMS microphones need to be assembled in a very small volume, which may limit their thermal stability and sensitivity. Therefore, in some application scenarios, the sensitivity of MEMS microphones is insufficient. Summary of the invention

[0006] In order to overcome the defects in the above-mentioned prior art, the present invention provides a low-cost precision microphone based on a MEMS microphone, which averages the output noise of active electronic devices by connecting the outputs of multiple unrelated noise sources in parallel, and ultimately reduces the background noise of the overall output, thereby improving the signal-to-noise ratio.

[0007] To achieve the above object, the present invention adopts the following technical solutions, including:

[0008] A low-cost precision microphone based on a MEMS microphone uses the superposition of MEMS microphone signals from multiple channels to reduce the background noise of the microphone; the noise of each channel is independent and unrelated to each other.

[0009] Preferably, it comprises: a MEMS microphone carrier board, a preamplifier and an output interface;

[0010] The MEMS microphone carrier includes a plurality of MEMS microphones connected in parallel, and the MEMS microphones are used to collect sound signals;

[0011] The preamplifier includes an operational amplifier module; wherein the operational amplifier module includes a plurality of operational amplifiers connected in parallel, and the input nodes of each operational amplifier are respectively connected to the output nodes of each MEMS microphone, so as to amplify the sound signal received by the MEMS microphone; the preamplifier superimposes the outputs of the plurality of operational amplifiers connected in parallel;

[0012] The output interface is used to output the output signal of the preamplifier.

[0013] Preferably, the preamplifier further includes: an IEPE power supply module and a voltage follower module;

[0014] The power supply voltage end of the IEPE power supply module is respectively connected to the operational amplifier module and the voltage follower module, and is used to power the operational amplifier in the voltage follower module and the operational amplifier module; the power supply voltage end of the IEPE power supply module is also connected to the MEMS microphone, and is used to power the MEMS microphone;

[0015] The reference voltage terminal of the IEPE power supply module is connected to the input terminal of the voltage follower module, and is used to input the voltage divided by the voltage divider resistor in the IEPE power supply module into the voltage follower module; the output terminal of the voltage follower module is connected to the operational amplifier module, and is used to stabilize the voltage, provide the operational amplifier module with a reference voltage with a stable voltage value, and reduce the influence of noise or interference on the circuit.

[0016] Preferably, the preamplifier further comprises: a DC bias module;

[0017] The input end of the DC bias module is connected to the output end of the operational amplifier module, and the output end of the DC bias module is connected to the positive electrode of the output interface. The outputs of multiple parallel operational amplifiers are connected together through an average resistor and finally connected to the anode of the Zener diode in the DC bias module. The cathode of the Zener diode is directly connected to the positive electrode of the output interface. The Zener diode always generates a stable DC bias voltage between the cathode and the anode, so that the configured output signal is the DC bias voltage of the Zener diode plus the output AC signal.

[0018] Preferably, the IEPE power supply module includes: a voltage stabilizing diode U2, a resistor R3, a resistor R5, a resistor R7, a resistor R11, a resistor R12 and a capacitor C3;

[0019] Among them, the series combination of resistor R5 and resistor R11, the series combination of resistor R7 and resistor R12 and the capacitor C3 are connected in parallel, forming three parallel loops connected between the power supply voltage terminal and the ground, and the other end of the resistor R11 and the other end of the resistor R12 are grounded respectively, and the other end of the resistor R5 and the other end of the resistor R7 are connected to the power supply voltage terminal respectively; one end of the resistor R3 is connected to the positive electrode of the output interface, and the other end of the resistor R3 is connected to the power supply voltage terminal; the anode end of the voltage zener diode U2 is grounded, and the cathode end is connected to the power supply voltage terminal; the reference end is connected to one end where the resistor R5 and the resistor R11 are connected.

[0020] Preferably, the voltage follower module includes: an operational amplifier U6 and a capacitor C9;

[0021] Among them, the negative power supply terminal of the operational amplifier U6 is grounded, and the positive power supply terminal is connected to the power supply voltage terminal; the in-phase input terminal of the operational amplifier U6 is connected to one end of the resistor R7 and the resistor R12 in the IEPE power supply module and is connected to the ground with the filter capacitor C9; the inverting input terminal of the operational amplifier U6 is connected to the output terminal of the operational amplifier U6, and the output terminal of the operational amplifier U6 serves as the output terminal of the voltage follower module.

[0022] Preferably, the operational amplifier module includes: a circuit structure consisting of an operational amplifier U1, a resistor R1, a resistor R2, a resistor R4, a resistor R6, a capacitor C1, and a capacitor C2; a circuit structure consisting of an operational amplifier U4, a resistor R9, a resistor R10, a resistor R14, a resistor R15, a capacitor C5, and a capacitor C6; and a circuit structure consisting of an operational amplifier U5, a resistor R16, a resistor R17, a resistor R18, a resistor R19, a capacitor C7, and a capacitor C8; the three circuit structures are exactly the same and are connected in parallel to form an operational amplifier module;

[0023] Among them, the negative power supply terminals of the operational amplifier U1, the operational amplifier U4, and the operational amplifier U5 are all grounded, and the positive power supply terminals are all connected to the power supply voltage terminal and are simultaneously connected to the capacitors C1, C5, and C7 to the ground; the capacitors C2, C6, and C8 are correspondingly connected between the output nodes of the three MEMS microphones and the in-phase input terminals of the operational amplifiers U1, U4, and U5; one end of the resistors R6, R15, and R19 are all connected to the output terminal of the voltage follower module, and the other ends of the resistors R6, R15, and R19 are correspondingly connected to the in-phase input terminals of the operational amplifiers U1, U4, and U5; one end of the resistors R1, R9, and R16 is correspondingly connected to the resistors R 2. Resistor R10 and resistor R17 are connected in series; the other ends of resistor R1, resistor R9 and resistor R16 are all connected to the output end of the voltage follower module; the inverting input ends of operational amplifier U1, operational amplifier U4 and operational amplifier U5 are correspondingly connected to one end where resistor R1 and resistor R2 are connected, one end where resistor R9 and resistor R10 are connected, and one end where resistor R16 and resistor R17 are connected; resistor R2, resistor R10 and resistor R17 are correspondingly connected to the output ends of operational amplifier U1, operational amplifier U4 and operational amplifier U5, and at the same time are correspondingly connected to one end of resistor R4, resistor R14 and resistor R18; the other ends of resistor R4, resistor R14 and resistor R18 are connected together as the output end of the operational amplifier module.

[0024] Preferably, the DC bias module includes: a voltage stabilizing diode U3, a resistor R8, a resistor R13 and a capacitor C4;

[0025] Among them, the resistor R8 and the resistor R13 are connected in series and then connected in parallel with the capacitor C4, forming two parallel circuits connected between the output end of the operational amplifier module and the positive electrode J6 of the output interface; the anode end of the Zener diode U3 is connected to the output end of the operational amplifier module; the cathode end of the Zener diode U3 is connected to the positive electrode of the output interface; the reference end of the Zener diode U3 is connected to one end where the resistor R8 and the resistor R13 are connected.

[0026] Preferably, it includes three MEMS microphones connected in parallel and three corresponding operational amplifiers connected in parallel; the three MEMS microphones are evenly arranged in a circular array at an angle of 120 degrees; the output interface adopts a BNC interface, and the negative electrode J7 of the output interface is connected to the ground.

[0027] Preferably, it also includes: a microphone housing;

[0028] The MEMS microphone carrier circuit and preamplifier circuit are distributed on two PCB boards; the MEMS microphone carrier circuit board is placed on the front face of the microphone housing, parallel to the front face of the housing and the side of the MEMS microphone carrier with the sound inlet is external; the preamplifier circuit board is placed horizontally inside the microphone housing and perpendicular to the MEMS microphone carrier circuit board; the output interface is placed on the rear face of the microphone housing; the microphone housing is a metal structure.

[0029] The advantages of the present invention are:

[0030] (1) The present invention uses multiple MEMS microphone elements in parallel, taking advantage of the good consistency of amplitude and phase and small discreteness of MEMS microphones to collect sound signals, amplifies the received sound signals using a preamplifier circuit, and then combines them and transmits them to the collection device after DC bias.

[0031] (2) The present invention evenly mounts multiple MEMS microphones in a circular array on the same PCB board, so that the output signals of the multiple MEMS microphones are merged after amplification. Since the active electronic devices in the microphone will generate random electrical noise, the outputs of multiple unrelated noise sources are connected in parallel, and the output noise is averaged, ultimately reducing the overall output background noise of the microphone, thereby improving the signal-to-noise ratio of the output signal.

[0032] (3) The present invention uses a MEMS microphone. The material cost used in the MEMS microphone is relatively low, and by simplifying the design of mechanical and electronic components, the complex process steps and related costs in the manufacturing process are further reduced. Compared with traditional condenser microphones, MEMS microphones excel in cost control, which makes the present invention more cost-effective.

[0033] (4) Since the noise of each channel is independent and uncorrelated, the background noise of the microphone can be better reduced by adding more channels, thereby improving the signal-to-noise ratio of the microphone; by adding an adder circuit at the output end of the operational amplifier module, the signals of each channel are accumulated, which can improve the signal-to-noise ratio and reduce the acquisition time to a certain extent, thereby improving the resolution of the microphone. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 FIG. 4 is a circuit diagram of the MEMS microphone carrier board of the present invention.

[0035] Figure 2 4 is a circuit diagram of the preamplifier in the present invention.

[0036] Figure 3 It is the overall circuit diagram of the present invention.

[0037] Figure 4It is a structural schematic diagram of the present invention.

[0038] Figure 5 The figure shows the calculation results of the total noise value of single-channel and three-channel circuits.

[0039] Figure 6 Figure 2 is the total noise power spectral density diagram for single-channel and three-channel circuits. DETAILED DESCRIPTION

[0040] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0041] A low-cost precision microphone based on a MEMS microphone comprises a microphone housing, a MEMS microphone carrier board, a preamplifier and an output interface.

[0042] The MEMS microphone carrier includes three parallel MEMS microphones arranged evenly in a circular array, with small through-hole pads arranged around them for necessary power and signal connections. In this embodiment, the three MEMS microphones are evenly arranged at an angle of 120 degrees to form a circular array.

[0043] The preamplifier includes an IEPE power supply module, a voltage follower module, an operational amplifier module and a DC bias module, and the four modules are placed on the same circuit board.

[0044] The 3.3V node in the MEMS microphone carrier is connected to the 3.3V node in the IEPE power supply module to provide a 3.3V voltage for the MEMS microphone carrier. The ground node in the MEMS microphone carrier is connected to the ground node in the IEPE power supply module. The operational amplifier module includes three parallel operational amplifiers, and the input nodes of each operational amplifier are respectively connected to the output nodes of each MEMS microphone in a point-to-point distribution, so as to amplify the sound signal received by the MEMS microphone.

[0045] The 3.3V power supply voltage terminal of the IEPE power supply module is respectively connected to the voltage follower module and the operational amplifier module, and is used to provide a 3.3V voltage to the positive electrode of the operational amplifier in the voltage follower module and the operational amplifier module; the power supply voltage terminal of the IEPE power supply module is also connected to the MEMS microphone, and is used to power the MEMS microphone.

[0046] The reference voltage terminal in the IEPE power supply module is connected to the input terminal of the voltage follower module, and the V / 2 voltage divided by the voltage divider resistor in the IEPE power supply module is input into the voltage follower module.

[0047] The output end of the voltage follower module is connected to the operational amplifier module for stabilizing the voltage, providing the operational amplifier module with a V / 2 reference voltage with a stable voltage value, and reducing the influence of noise or interference on the circuit.

[0048] The voltage follower module and the operational amplifier in the operational amplifier module are powered by a single +3.3V power supply. A virtual ground is required during operation, and the reference voltage is V / 2.

[0049] The output interface uses a BNC interface. The output end of the operational amplifier module is connected to the input end of the DC bias module, and the output end of the DC bias module is connected to the positive pole of the BNC interface. The outputs of the three operational amplifiers are connected together through an average resistor and finally connected to the anode of the Zener diode in the DC bias module. The cathode of the Zener diode is directly connected to the positive pole of the BNC interface, so that the Zener diode will always generate a stable DC bias voltage between the cathode and the anode, so that the configured output signal is the DC bias voltage of the Zener diode plus the output AC signal.

[0050] The output signal conditioned by the preamplifier will be connected to the BNC interface through a wire. The BNC interface has excellent signal transmission and shielding performance, which can ensure the transmission quality and accuracy of the signal. The measurement personnel can transmit the sound signal to the data acquisition device or computer and other equipment through the BNC interface for further analysis and processing.

[0051] The DC bias module and the IEPE power supply module are both connected to the positive terminal of the BNC interface, and the negative terminal of the BNC interface is grounded, which is used for the input of IEPE current and the output of sound signals.

[0052] The microphone of the present invention uses multiple MEMS microphone elements in parallel, and takes advantage of the good consistency of the amplitude and phase of the MEMS microphone and the small discreteness, so as to accurately and effectively collect sound signals, amplify the received sound signals by the preamplifier circuit, merge them, and transmit them to the collection device after DC bias. During this period, the active components will generate random electrical noise signals. The microphone averages the output noise of the active electronic devices by connecting the outputs of multiple unrelated noise sources in parallel, and finally reduces the overall output background noise, thereby improving the signal-to-noise ratio of the signal.

[0053] The microphone of the present invention adopts the signal output type and power supply mode of IEPE, introduces an IEPE power supply as a constant current output to the MEMS microphone, and generates an output voltage through the IEPE power supply module in the preamplifier to power other parts of the microphone; at the same time, the output signal of the preamplifier is efficiently transmitted to the measuring equipment through the BNC interface.

[0054] Depend on Figure 1 and Figure 3 As shown, the circuit of the MEMS microphone carrier of the present invention is as follows: the MEMS microphone carrier includes three MEMS microphones of the same model, namely MEMS microphone U7, MEMS microphone U8, and MEMS microphone U9. The three MEMS microphones are connected in parallel, the positive node Vcc is connected to the 3.3V power supply voltage terminal of the IEPE power supply module, the output node OUT is connected to the input node of the corresponding operational amplifier in the preamplifier; the remaining nodes are all grounded.

[0055] Depend on Figure 2 and Figure 3 As shown, the circuit of the preamplifier part of the present invention is as follows:.

[0056] The IEPE power supply module includes: a voltage regulator diode U2, a resistor R3, a resistor R5, a resistor R7, a resistor R11, a resistor R12, and a capacitor C3. The series combination of the resistor R5 and the resistor R11 is connected in parallel with the series combination of the resistor R7 and the resistor R12 and the capacitor C3 to form three parallel circuits connected between the 3.3V power supply voltage terminal and the ground, and the other end of the resistor R11 and the other end of the resistor R12 are respectively connected to the ground, and the other end of the resistor R5 and the other end of the resistor R7 are respectively connected to the 3.3V power supply voltage terminal; one end of the resistor R3 is connected to the positive electrode of the BNC interface, and the other end of the resistor R3 is connected to the 3.3V power supply voltage terminal; the anode end of the voltage regulator diode U2 is grounded; the cathode end of the voltage regulator diode U2 is connected to the 3.3V power supply voltage terminal; the reference end of the voltage regulator diode U2 is connected to one end where the resistor R5 and the resistor R11 are connected.

[0057] The voltage follower module includes: an operational amplifier U6 and a capacitor C9; the 2nd pin of the operational amplifier U6 is the negative power supply terminal connected to the ground, and the 5th pin is the positive power supply connected to the 3.3V power supply voltage terminal; the 1st pin of the operational amplifier U6 is the in-phase input terminal connected to the end where the resistor R7 and the resistor R12 in the IEPE power supply module are connected, and is also connected to the ground with the filter capacitor C9; the 3rd pin of the operational amplifier U6 is the inverting input terminal directly connected to the 4th pin of the operational amplifier U6, i.e., the output terminal, and the output terminal of the operational amplifier U6 is used as the output terminal of the voltage follower module.

[0058] The operational amplifier module includes: a circuit structure consisting of an operational amplifier U1, a resistor R1, a resistor R2, a resistor R4, a resistor R6, a capacitor C1, and a capacitor C2; a circuit structure consisting of an operational amplifier U4, a resistor R9, a resistor R10, a resistor R14, a resistor R15, a capacitor C5, and a capacitor C6; and a circuit structure consisting of an operational amplifier U5, a resistor R16, a resistor R17, a resistor R18, a resistor R19, a capacitor C7, and a capacitor C8; the three circuit structures are exactly the same and are connected in parallel to form an operational amplifier module. Among them, the 2nd pins of the operational amplifier U1, the operational amplifier U4, and the operational amplifier U5 are all connected to the negative power supply terminal and the 6th pins are all connected to the positive power supply terminal and the 3.3V power supply voltage terminal, and the capacitors C1, C5, and C7 are connected to the ground respectively; the capacitors C2, C6, and C8 are respectively connected between the output nodes of the three MEMS microphones in the MEMS microphone carrier and the 3rd pins, i.e., the in-phase input terminals, of the operational amplifier U1, the operational amplifier U4, and the operational amplifier U5; one end of the resistors R6, R15, and R19 are connected to the output terminal of the voltage follower module, and the other ends of the resistors R6, R15, and R19 are respectively connected to the 3rd pins, i.e., the in-phase input terminals, of the operational amplifier U1, the operational amplifier U4, and the operational amplifier U5; the resistors R1, R9, and R One end of 16 is connected in series with resistors R2, R10, and R17 respectively; the other ends of resistors R1, R9, and R16 are connected to the output end of the voltage follower module respectively; the 4th pin, i.e., the inverting input end, of the operational amplifier U1, the operational amplifier U4, and the operational amplifier U5 are respectively connected to the end connected to resistor R1 and resistor R2, the end connected to resistor R9 and resistor R10, and the end connected to resistor R16 and resistor R17; the resistors R2, R10, and R17 are respectively connected to the 1st pin, i.e., the output end, of the operational amplifier U1, the operational amplifier U4, and the operational amplifier U5, and are respectively connected to one end of the resistors R4, R14, and R18; the other ends of the resistors R4, R14, and R18 are connected together as the output end of the operational amplifier module.

[0059] The DC bias module includes: a voltage regulator diode U3, a resistor R8, a resistor R13 and a capacitor C4; the resistor R8 and the resistor R13 are connected in series and then connected in parallel with the capacitor C4 to form two parallel circuits connected between the output end of the operational amplifier module and the positive electrode of the BNC interface; the anode end of the voltage regulator diode U3 is connected to the output end of the operational amplifier module; the cathode end of the voltage regulator diode U3 is connected to the positive electrode of the BNC interface; the reference end of the voltage regulator diode U3 is connected to one end where the resistor R8 and the resistor R13 are connected.

[0060] The MEMS microphone carrier circuit and preamplifier circuit are distributed on two PCB boards, forming the circuit part of the microphone. Figure 4As shown, the MEMS microphone carrier circuit board is placed on the front face of the microphone housing, parallel to the front face of the housing and the side of the MEMS microphone carrier with the sound inlet is placed externally; the preamplifier circuit board is placed horizontally inside the microphone housing and perpendicular to the MEMS microphone carrier circuit board; the BNC interface is placed on the rear face of the microphone housing and is connected to the microphone housing by a screw. The microphone housing is divided into upper and lower parts; the lower housing is used to load the MEMS microphone carrier, preamplifier and BNC interface; the upper housing and the lower housing are combined to form a closed structure; the microphone housing is a metal structure used to shield the internal electrical signal and reduce the electrical noise of the microphone.

[0061] The microphone of the present invention is tested according to the following simulation experiment:

[0062] Multisim has a professional noise analysis function, which is used to analyze the impact of noise on circuit performance. In Multisim, noise analysis is performed on single-channel and three-channel superimposed circuits.

[0063] Simulation process:

[0064] The total noise value and noise power spectrum density curve are simulated and calculated respectively. The noise signal simulated by Multisim is set as the input noise reference source, the output of the operational amplifier module of the preamplifier is set as the output node, and GND is used as the reference node. The starting frequency is set to 20Hz, the stop frequency is 20kHz, and the scanning type is ten times the frequency band. When calculating the noise power spectrum density curve, the number of summation points is set to 1 each time, and the total output noise of the circuit is selected as the variable.

[0065] Figure 5 The total noise value of the circuit calculated for noise analysis. When collecting signals, white noise will be introduced when the sound signal passes through the equipment. The background noise of the microphone preamplifier is mainly provided by the operational amplifier, resistor, capacitor and voltage regulator diode. Figure 5 As shown in (a) of FIG. 1 , the total signal output noise of the single-channel circuit is 13.15 μV; Figure 5 As shown in (b), the total output noise of the three-channel superposition circuit signal is 7.59μV, and the total input and output noise of the three-channel superposition circuit signal are reduced to about three-fifths of the original. This shows that this signal superposition method can effectively reduce circuit noise.

[0066] Figure 6 This is a comparison of the total noise power spectrum density curves of a single-channel circuit and a three-channel superposition circuit. The simulation signal frequency is between 20HZ and 20MHZ. Figure 6 As shown in (a) of the figure, the output signal noise power density of the single-channel circuit is Lower to around And it is stable in the frequency range of 2kHz~100kHz Then gradually decrease; Figure 6 As shown in (b), the output signal noise power density of the three-channel circuit is Lower to around And it is stable in the frequency range of 2kHz~100kHz Around, and then gradually decreased. Figure 6 It shows that within the range of simulation signal frequency from 20HZ to 20MHZ, after the electrical signal is superimposed through three channels, the power spectrum density curve of the overall output circuit noise is flatter than that of a single channel, and the overall noise level is reduced.

[0067] Through the analysis of the calculation data and images of the noise analysis, it can be seen that even if the three-channel signal superposition circuit uses more operational amplifiers and electronic devices such as resistors and capacitors, and generates more circuit noise, the total circuit output and input noise are significantly reduced compared to the single-channel signal circuit after the three-channel superposition noise reduction is performed by utilizing the randomness of the noise. And from the analysis of the power spectrum density diagram of the total noise, it can be seen that the output and input circuit noise of the three-channel superposition circuit not only has a significant decrease in overall size, but also has a more uniform distribution at each frequency, which can prove the applicability of the invention in theory.

[0068] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A low-cost precision microphone based on a MEMS microphone, characterized in that: The MEMS microphone signals of multiple channels are superimposed to reduce the background noise of the microphone; the noise of each channel is independent and unrelated.

2. A low-cost precision microphone based on a MEMS microphone according to claim 1, characterized in that: include: MEMS microphone carrier board, preamplifier and output interface; The MEMS microphone carrier includes a plurality of MEMS microphones connected in parallel, and the MEMS microphones are used to collect sound signals; The preamplifier includes an operational amplifier module; wherein the operational amplifier module includes a plurality of operational amplifiers connected in parallel, and the input nodes of each operational amplifier are respectively connected to the output nodes of each MEMS microphone, so as to amplify the sound signal received by the MEMS microphone; the preamplifier superimposes the outputs of the plurality of operational amplifiers connected in parallel; The output interface is used to output the output signal of the preamplifier.

3. A low-cost precision microphone based on a MEMS microphone according to claim 2, characterized in that: The preamplifier also includes: an IEPE power supply module and a voltage follower module; The power supply voltage end of the IEPE power supply module is respectively connected to the operational amplifier module and the voltage follower module, and is used to power the operational amplifier in the voltage follower module and the operational amplifier module; the power supply voltage end of the IEPE power supply module is also connected to the MEMS microphone, and is used to power the MEMS microphone; The reference voltage terminal of the IEPE power supply module is connected to the input terminal of the voltage follower module, and is used to input the voltage divided by the voltage divider resistor in the IEPE power supply module into the voltage follower module; the output terminal of the voltage follower module is connected to the operational amplifier module, and is used to stabilize the voltage, provide the operational amplifier module with a reference voltage with a stable voltage value, and reduce the influence of noise or interference on the circuit.

4. A low-cost precision microphone based on a MEMS microphone according to claim 2, characterized in that: The preamplifier also includes: a DC bias module; The input end of the DC bias module is connected to the output end of the operational amplifier module, and the output end of the DC bias module is connected to the positive electrode of the output interface. The outputs of multiple parallel operational amplifiers are connected together through an average resistor and finally connected to the anode of the Zener diode in the DC bias module. The cathode of the Zener diode is directly connected to the positive electrode of the output interface. The Zener diode always generates a stable DC bias voltage between the cathode and the anode, so that the configured output signal is the DC bias voltage of the Zener diode plus the output AC signal.

5. A low-cost precision microphone based on a MEMS microphone according to claim 3, characterized in that: The IEPE power supply module includes: a voltage stabilizing diode U2, a resistor R3, a resistor R5, a resistor R7, a resistor R11, a resistor R12 and a capacitor C3; Among them, the series combination of resistor R5 and resistor R11, the series combination of resistor R7 and resistor R12 and the capacitor C3 are connected in parallel, forming three parallel loops connected between the power supply voltage terminal and the ground, and the other end of the resistor R11 and the other end of the resistor R12 are grounded respectively, and the other end of the resistor R5 and the other end of the resistor R7 are connected to the power supply voltage terminal respectively; one end of the resistor R3 is connected to the positive electrode of the output interface, and the other end of the resistor R3 is connected to the power supply voltage terminal; the anode end of the voltage zener diode U2 is grounded, and the cathode end is connected to the power supply voltage terminal; the reference end is connected to one end where the resistor R5 and the resistor R11 are connected.

6. A low-cost precision microphone based on a MEMS microphone according to claim 5, characterized in that: The voltage follower module includes: an operational amplifier U6 and a capacitor C9; Among them, the negative power supply terminal of the operational amplifier U6 is grounded, and the positive power supply terminal is connected to the power supply voltage terminal; the in-phase input terminal of the operational amplifier U6 is connected to one end of the resistor R7 and the resistor R12 in the IEPE power supply module and is connected to the ground with the filter capacitor C9; the inverting input terminal of the operational amplifier U6 is connected to the output terminal of the operational amplifier U6, and the output terminal of the operational amplifier U6 serves as the output terminal of the voltage follower module.

7. A low-cost precision microphone based on a MEMS microphone according to claim 2, characterized in that: The operational amplifier module includes: a circuit structure composed of an operational amplifier U1, a resistor R1, a resistor R2, a resistor R4, a resistor R6, a capacitor C1, and a capacitor C2; a circuit structure composed of an operational amplifier U4, a resistor R9, a resistor R10, a resistor R14, a resistor R15, a capacitor C5, and a capacitor C6; and a circuit structure composed of an operational amplifier U5, a resistor R16, a resistor R17, a resistor R18, a resistor R19, a capacitor C7, and a capacitor C8; the three circuit structures are completely the same and are connected in parallel to form an operational amplifier module; Among them, the negative power supply terminals of the operational amplifier U1, the operational amplifier U4, and the operational amplifier U5 are all grounded, and the positive power supply terminals are all connected to the power supply voltage terminal and are simultaneously connected to the capacitors C1, C5, and C7 to the ground; the capacitors C2, C6, and C8 are correspondingly connected between the output nodes of the three MEMS microphones and the in-phase input terminals of the operational amplifiers U1, U4, and U5; one end of the resistors R6, R15, and R19 are all connected to the output terminal of the voltage follower module, and the other ends of the resistors R6, R15, and R19 are correspondingly connected to the in-phase input terminals of the operational amplifiers U1, U4, and U5; one end of the resistors R1, R9, and R16 is correspondingly connected to the resistors R 2. Resistor R10 and resistor R17 are connected in series; the other ends of resistor R1, resistor R9 and resistor R16 are all connected to the output end of the voltage follower module; the inverting input ends of operational amplifier U1, operational amplifier U4 and operational amplifier U5 are correspondingly connected to one end where resistor R1 and resistor R2 are connected, one end where resistor R9 and resistor R10 are connected, and one end where resistor R16 and resistor R17 are connected; resistor R2, resistor R10 and resistor R17 are correspondingly connected to the output ends of operational amplifier U1, operational amplifier U4 and operational amplifier U5, and at the same time are correspondingly connected to one end of resistor R4, resistor R14 and resistor R18; the other ends of resistor R4, resistor R14 and resistor R18 are connected together as the output end of the operational amplifier module.

8. The low-cost precision microphone based on a MEMS microphone according to claim 4, characterized in that: The DC bias module includes: a voltage stabilizing diode U3, a resistor R8, a resistor R13 and a capacitor C4; Among them, the resistor R8 and the resistor R13 are connected in series and then connected in parallel with the capacitor C4, forming two parallel circuits connected between the output end of the operational amplifier module and the positive electrode J6 of the output interface; the anode end of the Zener diode U3 is connected to the output end of the operational amplifier module; the cathode end of the Zener diode U3 is connected to the positive electrode of the output interface; the reference end of the Zener diode U3 is connected to one end where the resistor R8 and the resistor R13 are connected.

9. The low-cost precision microphone based on a MEMS microphone according to claim 1, characterized in that: It includes three parallel MEMS microphones and corresponding three parallel operational amplifiers; the three MEMS microphones are evenly arranged in a circular array at an angle of 120 degrees; the output interface adopts a BNC interface, and the negative electrode J7 of the output interface is connected to the ground.

10. A low-cost precision microphone based on a MEMS microphone according to any one of claims 1 to 9, characterized in that: Also includes: Microphone housing; The MEMS microphone carrier circuit and preamplifier circuit are distributed on two PCB boards; the MEMS microphone carrier circuit board is placed on the front face of the microphone housing, parallel to the front face of the housing and the side of the MEMS microphone carrier with the sound inlet is external; the preamplifier circuit board is placed horizontally inside the microphone housing and perpendicular to the MEMS microphone carrier circuit board; the output interface is placed on the rear face of the microphone housing; the microphone housing is a metal structure.

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