CN117425118A - Low-power-consumption and low-noise capacitive MEMS microphone reading circuit - Google Patents
Low-power-consumption and low-noise capacitive MEMS microphone reading circuit Download PDFInfo
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- CN117425118A CN117425118A CN202311671863.7A CN202311671863A CN117425118A CN 117425118 A CN117425118 A CN 117425118A CN 202311671863 A CN202311671863 A CN 202311671863A CN 117425118 A CN117425118 A CN 117425118A
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
- H04R19/00—Electrostatic transducers
- H04R19/04—Microphones
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- Acoustics & Sound (AREA)
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- Electrostatic, Electromagnetic, Magneto- Strictive, And Variable-Resistance Transducers (AREA)
Abstract
A low-power consumption and low-noise capacitive MEMS microphone reading circuit belongs to the field of monitoring. Comprises a charge pump, a gain amplifier, a sigma delta analog-to-digital converter, a decimator, a low pass filter and a tri-state controller module; the charge pump provides stable direct-current voltage for the microphone, and keeps the charge stored in the microphone capacitor unchanged; when sound pressure acts on the diaphragm, the microphone converts the sound pressure level into a voltage signal changing between two polar plates, and the voltage signal output by the microphone passes through the gain amplifier to generate a stable output signal for the sigma delta analog-to-digital converter; the sigma delta analog-to-digital converter converts an input analog signal into a series of pulse density modulated signals; the decimator encodes the unit pulse density modulation signal into a multi-bit pulse code modulation signal; the low-pass filter filters out high-frequency components in the multi-bit encoded signal and increases the output bandwidth of the decimator; the tri-state controller confirms whether the output data is a left channel or a right channel according to the high-low level of the channel selection port.
Description
Technical Field
The invention belongs to the field of fault monitoring, and particularly relates to a readout circuit for a capacitive MEMS microphone.
Background
In a substation, the main devices are transformers, switches, capacitors, reactors, etc. The master devices within the station may be noisy in operation due to vibrations, the sources of operational noise typically being: the vibration noise of the equipment; resonance noise previously generated by the device; vibration noise generated by high-frequency harmonic waves of the system; electromagnetic vibration noise between devices; vibration noise between the equipment support and the foundation, etc., wherein the vibration noise of the equipment itself is dominant.
Along with the increase of the operation years of the equipment in the stations, the abnormal noise phenomenon is increased gradually besides the normal noise. The abnormal noise indicates that the apparatus is in an abnormal operation state.
Through the differences in loudness, tone and the like, experienced patrol personnel can distinguish the abnormal sound position and the current state of the equipment from noisy sounds, and distinguish the abnormal sound generation reasons according to the characteristics of the sounds.
Therefore, the accurate and proper signal detection and processing test means are found by utilizing the noise signals sent by the electrical equipment, and are key for realizing abnormal sound defect diagnosis of the substation equipment.
The sensor used in sound measurement and evaluation is called a microphone, which is a transducer device that converts an acoustic signal into an electrical signal, the quality and performance of which directly determine the performance of the measurement system.
In the traditional field of non-precision detection microphones (1/2 or 1/4 inch microphones used for precision measurement such as a sound level meter), electret microphones and MEMS microphones (also called sound sensors) are widely used.
The MEMS sound sensor is a sound sensor based on micro-electromechanical system (MEMS) technology, and has the characteristics of small size, low power consumption, high sensitivity and the like.
The working principle of the MEMS sound sensor is that a micro sound sensor element is manufactured by utilizing the MEMS technology, and sound wave signals are converted into electric signals through piezoelectric materials in the element. The working principle ensures that the MEMS sound sensor has the characteristics of high sensitivity and quick response, and can accurately capture the sound in the environment.
With the rapid development of MEMS microphones, the advantages are more evident as shown in table 1 below:
table 1 microphone performance comparison
The advantages of MEMS microphones can be summarized by comparing the parameters of MEMS and conventional electret microphones (ECM) in the above table: the integrated level is high, the packaging performance is good, and the influence of external temperature and vibration on the acquisition signal of the microphone is small; mass production using integrated circuit technology results in a lower microphone cost; the MEMS microphone has low power consumption and is tiny and easy to integrate, and the volume of the MEMS microphone is only about 1/6 of the size of the nail cover. Therefore, the MEMS microphone is particularly suitable for microphone array application with high cost performance, and is widely applied in the fields of factory noise monitoring, machine fault diagnosis and the like.
The requirements of the abnormal sound signal acquisition of the power equipment on the microphone parameters are shown in table 2 by combining the characteristics of the noise signals of the power equipment.
Table 2 abnormal audible signal acquisition of electrical equipment requires microphone parameters
| Parameters (parameters) | Range |
| Frequency response/(Hz-kHz) | 20Hz-30kHz |
| sensitivity/(mV/pa) | ≥3.8Mv/Pa |
| Sensitivity level/dB | ≤47dB |
| Linear range/dB | 45dB-110dB |
As can be seen from tables 1 and 2: basic parameters of the electret microphone and the MEMS microphone can meet the requirements of acquisition of acoustic signals of power equipment of a transformer substation, but the characteristics of low cost, low power consumption and strong impact interference resistance of the MEMS microphone make the MEMS microphone particularly suitable for use in a power detection scene.
As can be seen from the working principle of the capacitive MEMS microphone, the MEMS microphone readout circuit is generally composed of two parts, one part is used for providing stable direct current bias voltage for the normal operation of the MEMS microphone, and the other part is a preamplifier circuit used for reading and processing small signals generated by the MEMS microphone.
The microphone generates a very small signal amplitude under the action of sound pressure, so that the noise of the reading circuit is required to be very low.
The patent of the invention, entitled "Dual pickup Signal noise reduction System and method with Spectrum subtraction" is disclosed by the invention of attuned publication No. 2004.11.10, entitled "CN 1175709C," in which speech enhancement is provided by employing linear convolution, causal filtering, and/or some spectral subtraction algorithms that exponentially average the spectral subtraction gain function by frequency spectrum. When a far mouth pickup is used in conjunction with a near mouth pickup, non-stationary background noise can be handled as long as the noise spectrum can be estimated from a single input sample block. The far mouth pickup picks up speaker's voice in addition to background noise, but the resulting level is lower than the near mouth pickup. To enhance the noise estimation, a spectral subtraction stage is used to suppress speech in the far mouth pickup signal. To enhance the noise estimate, a coarse speech estimate is formed from the near-mouth signal using another spectral subtraction stage. Finally, a third spectral subtraction function is used to enhance the near-mouth signal by suppressing background noise with the enhanced background noise estimate. The technical scheme adopts three frequency spectrum subtraction functions to inhibit background noise, so that the microphone reading circuit module is complex in structure, and more electronic elements are adopted, thereby being unfavorable for reducing the whole volume of the microphone on one hand, and influencing the service life of the microphone in the actual use process due to higher energy consumption and higher failure rate on the other hand.
The invention patent application with the application publication number of CN 109963231A discloses a vocal music microphone audio processor, which comprises a first capacitor, a ninth capacitor, a first resistor, a sixth resistor, a frequency modulation transmitting chip, a crystal oscillator, a transformer, a transistor and an antenna, wherein an audio radio signal is input into the frequency modulation transmitting chip through the first capacitor and the first resistor for processing by the microphone pickup, the processed signal is oscillated by an oscillating circuit formed by the transformer and the crystal oscillator, and finally the oscillated frequency signal is amplified by the transistor and then is sent by the antenna. According to the technical scheme, the frequency modulation transmitting chip is adopted to process signals, and then the processed signals are oscillated and amplified, so that signals with fewer clutters can be obtained, and the amplified signals are long in transmission distance and high in anti-interference capability. However, the system is based on discrete components, has limited transmission distance, is inconvenient to interface with various limited or wireless data transmission networks, and cannot meet the use requirements of the existing transformer substation equipment abnormal sound defect diagnosis system on low cost, low power consumption and strong impact interference resistance of the microphone no matter the system is of a whole volume or energy consumption.
Disclosure of Invention
The invention aims to provide a capacitive MEMS microphone reading circuit with low power consumption and low noise. A charge pump is adopted to provide stable direct current voltage for the MEMS microphone, and a voltage signal output by the microphone passes through a gain amplifier to generate a stable output signal for the sigma delta analog-to-digital converter; the sigma delta analog-to-digital converter converts an input analog signal into a series of pulse density modulated signals; the decimator encodes the unit pulse density modulation signal into a multi-bit pulse code modulation signal; the low-pass filter filters out high-frequency components in the multi-bit encoded signal and increases the output bandwidth of the decimator; the tri-state controller confirms whether the output data is a left channel or a right channel according to the high and low levels of the channel selection port; the microphone reading circuit with low power consumption and low noise meeting the use requirement is provided for the abnormal sound defect diagnosis system of the transformer substation equipment.
The technical scheme of the invention is as follows: the capacitive MEMS microphone reading circuit with low power consumption and low noise is provided, and is characterized in that:
the readout circuit at least comprises a charge pump, a gain amplifier, a sigma delta analog-to-digital converter, a decimator, a low pass filter and a tri-state controller module;
the charge pump provides stable direct-current voltage for the MEMS microphone so as to keep the charge stored in the microphone capacitor unchanged;
when sound pressure acts on the vibrating diaphragm, the MEMS microphone converts the sound pressure level into a voltage signal changing between two polar plates, and the voltage signal output by the microphone passes through the gain amplifier to generate a stable output signal for the sigma delta analog-to-digital converter;
the sigma delta analog-to-digital converter converts an input analog signal into a series of pulse density modulated signals;
the decimator encodes the unit pulse density modulation signal into a multi-bit pulse code modulation signal;
the low-pass filter filters out high-frequency components in the multi-bit encoded signal and increases the output bandwidth of the decimator;
the tri-state controller confirms whether the output data is a left channel or a right channel according to the high-low level of the channel selection port.
Specifically, the readout circuit is composed of two parts, one part provides stable direct current bias voltage for the normal operation of the MEMS microphone, and the other part is a preamplifier circuit for reading and processing small signals generated by the MEMS microphone.
The readout circuit has high integration level and good packaging property, the influence of external temperature and vibration on the acquisition signals of the microphone is small, and the cost of the microphone is lower by mass production of an integrated circuit process; the MEMS microphone has low power consumption and is tiny and easy to integrate, is beneficial to reducing the volume of the MEMS microphone, and is particularly suitable for microphone arrays.
Specifically, the MEMS microphone adopting the capacitive MEMS microphone reading circuit has the following characteristic parameters:
digital I of high-precision 24-bit data 2 S interface; signal-to-noise ratio: 61dBA; sensitivity: -26dBFS (50 mV/pa); frequency response range: 10Hz-100kHz; consumption current: 1.4mA; dynamic range: 33dB-120dB.
Specifically, the microphone adopting the microphone reading circuit adopts the following sensor packaging structure:
the MEMS microphone adopts a bottom hole structure and is directly welded on the PCB; a sound transmission hole is arranged on the PCB to guide sound into the microphone cavity; the PCB with the microphone is connected to the external environment; the PCB, together with the housing constituting the microphone cavity, forms an acoustic circuit element that can influence the frequency response of the microphone.
Further, the MEMS microphone reading circuit is arranged on a PCB, and a microphone hole is arranged on the PCB and used for introducing sound into the microphone cavity; a shell is arranged to form the periphery of the microphone cavity; the microphone cavity formed by the shell is a Helmholtz cavity structure, the cavity structure forms a resonant cavity, and the resonant cavity is connected with the outside through an inner cavity and a sound transmission hole.
Further, the MEMS microphone with the bottom hole is directly welded and fixed on the PCB.
Specifically, the diameter of the sound transmission hole is more than or equal to 0.25mm.
Preferably, the diameter of the sound transmission hole ranges from 0.5mm to 1mm.
Further, the resonant frequency of the resonant cavity is calculated according to the following formula:
wherein f b Is the resonant frequency; c is sound velocity, 340m/s; d is the diameter of the through hole, and mm; v is the volume of the cavity, mm 3 The method comprises the steps of carrying out a first treatment on the surface of the L is the depth of the cavity, mm.
Compared with the prior art, the invention has the advantages that:
1. according to the technical scheme, the microphone reading circuit is formed by adopting the module circuit with high integration level, so that the microphone reading circuit has the characteristics of low power consumption and low noise, and can completely meet the use requirement of the abnormal sound defect diagnosis system of substation equipment;
2. according to the technical scheme, the detection result of the microphone is directly converted into the digital signal, so that the measurement accuracy and stability of the microphone are guaranteed, and the quality of the acoustic measurement result is guaranteed;
3, the technical scheme of the invention has high integration level, good encapsulation, and small influence of external temperature and vibration on the acquisition signal of the microphone; mass production using integrated circuit technology results in a lower microphone cost; the microphone array is low in power consumption, tiny and easy to integrate, is particularly suitable for microphone array application with high cost performance, and is widely applied to the fields of factory noise monitoring, machine fault diagnosis and the like.
Drawings
FIG. 1 is a schematic diagram of the functional blocks of a MEMS microphone readout circuit of the present invention;
fig. 2 is a schematic diagram of a package structure of a MEMS microphone adopting the technical scheme of the present invention.
In the figure, 1 is a MEMS microphone, 2 is a PCB board, 3 is a sound transmission hole, 4 is a microphone cavity, and 5 is a shell.
Detailed Description
The invention is further described below with reference to the accompanying drawings.
The MEMS microphone readout circuit is typically comprised of two parts, one part providing a stable dc bias voltage for the proper operation of the MEMS microphone and the other part being a preamplifier circuit for reading and processing the small signals generated by the MEMS microphone.
The MEMS microphone is particularly suitable for microphone array application with high cost performance, and is widely applied in the fields of factory noise monitoring, machine fault diagnosis and the like.
In fig. 1, the MEMS microphone readout circuit comprises at least a charge pump, a gain amplifier, a ΣΔ analog-to-digital converter, a decimator, a low-pass filter and a tri-state controller module.
Specifically, the input end of the charge pump is connected with the VDD power supply end, the output end of the charge pump is connected with the input end of the gain amplifier through the acoustic transducer capacitor, and the output end of the gain amplifier is connected with the input end of the sigma delta analog-to-digital converter; the output end of the sigma delta analog-to-digital converter sequentially passes through the decimator and the low-pass filter and is connected with the input end of the tri-state controller; the channel SELECT port of the tri-state controller is connected to the SELECT control terminal. The output of the tri-state controller constitutes the DATA output DATA of the MEMS microphone.
The charge pump provides stable direct-current voltage for the MEMS microphone so as to keep the charge stored in the microphone capacitor unchanged; when sound pressure acts on the vibrating diaphragm, the MEMS microphone converts the sound pressure level into a voltage signal changing between two polar plates, and the voltage signal output by the microphone passes through the gain amplifier to generate a stable output signal for the sigma delta analog-to-digital converter; the sigma delta analog-to-digital converter converts an input analog signal into a series of pulse density modulated signals; the decimator encodes the unit pulse density modulation signal into a multi-bit pulse code modulation signal; the low-pass filter filters out high-frequency components in the multi-bit encoded signal and increases the output bandwidth of the decimator; the tri-state controller confirms whether the output data is a left channel or a right channel according to the high-low level of the channel selection port.
The main characteristic parameters of the final-selection MEMS microphone comprise the following parameters:
digital I of high precision 24 bit data 2 S interface;
signal to noise ratio: 61dBA;
sensitivity: -26dBFS (50 mV/pa);
frequency response range: 10Hz-100kHz;
consumption current: 1.4mA;
dynamic range: 33dB-120dB.
The sensor package structure adopting the MEMS microphone readout circuit is as follows:
after the MEMS microphone is packaged, the output is either a digital signal or an analog signal, and the selection is directly a digital signal, so that the measurement accuracy and stability are ensured mainly from the part of sound pressure measurement.
The MEMS microphone reading circuit is arranged on the PCB 2.
The MEMS microphone 1 with the bottom outlet is directly welded and fixed on the PCB board 2, and a sound transmission hole 3 is provided on the PCB board to introduce sound into the microphone cavity 4. The PCB with the MEMS microphone is then connected to the external environment. The PCB board, together with the housing 5, thus forms an acoustic circuit element that can influence the frequency response of the microphone.
The PCB board is directly bonded with the equipment shell through the bonding layer, and the packaging technology can provide reliable sealing for the acoustic interface and provide the shortest acoustic path, so that good acoustic measurement quality is ensured.
The diameter of the sound transmission hole 3 is 0.25mm or more, and a value of 0.5mm to 1mm is usually recommended.
The microphone cavity 4 forms a helmholtz cavity structure, which forms a resonator cavity comprising a relatively wide cross section, which is connected to the outside by the inner cavity 4 and the sound transmission aperture 3.
Further, the resonant frequency of the resonant cavity is calculated by the following formula:
f in b Is the resonant frequency; c is soundSpeed, 340m/s; d is the diameter of the through hole; v is the volume of the cavity, mm 3 The method comprises the steps of carrying out a first treatment on the surface of the L is the depth of the cavity mm.
In summary, the MEMS microphone readout circuit according to the present invention comprises two parts, one part providing a stable dc bias voltage for the normal operation of the MEMS microphone, and the other part being a preamplifier circuit for reading and processing the small signal generated by the MEMS microphone.
The MEMS microphone adopting the technical scheme is particularly suitable for microphone array application with high cost performance, and has wide application in the fields of factory noise monitoring, machine fault diagnosis and the like.
The invention can be widely applied to the field of noise monitoring or fault diagnosis of power equipment.
Claims (10)
1. A low-power consumption and low-noise capacitive MEMS microphone readout circuit is characterized in that the readout circuit at least comprises the following modules:
a charge pump, a gain amplifier, a ΣΔ analog-to-digital converter, a decimator, a low-pass filter, and a tri-state controller module;
the charge pump provides stable direct-current voltage for the MEMS microphone so as to keep the charge stored in the microphone capacitor unchanged;
when sound pressure acts on the vibrating diaphragm, the MEMS microphone converts the sound pressure level into a voltage signal changing between two polar plates, and the voltage signal output by the microphone passes through the gain amplifier to generate a stable output signal for the sigma delta analog-to-digital converter;
the sigma delta analog-to-digital converter converts an input analog signal into a series of pulse density modulated signals;
the decimator encodes the unit pulse density modulation signal into a multi-bit pulse code modulation signal;
the low-pass filter filters out high-frequency components in the multi-bit encoded signal and increases the output bandwidth of the decimator;
the tri-state controller confirms whether the output data is a left channel or a right channel according to the high-low level of the channel selection port.
2. The low power consumption, low noise capacitive MEMS microphone sensing circuit of claim 1, wherein the sensing circuit comprises two parts, one part providing a stable dc bias voltage for normal operation of the MEMS microphone and the other part being a preamplifier circuit for sensing and processing small signals generated by the MEMS microphone.
3. The low-power consumption and low-noise capacitive MEMS microphone readout circuit according to claim 1, wherein the readout circuit has high integration level, good packaging property, small influence of external temperature and vibration on microphone acquisition signals, and low cost due to mass production by using an integrated circuit technology; the MEMS microphone has low power consumption and is tiny and easy to integrate, is beneficial to reducing the volume of the MEMS microphone, and is particularly suitable for microphone arrays.
4. A low power consumption, low noise capacitive MEMS microphone sensing circuit according to claim 1, characterized by a MEMS microphone employing said capacitive MEMS microphone sensing circuit, characterized by the following parameters:
digital I of high-precision 24-bit data 2 S interface;
signal-to-noise ratio: 61dBA;
sensitivity: -26dBFS (50 mV/pa);
frequency response range: 10Hz-100kHz;
consumption current: 1.4mA;
dynamic range: 33dB-120dB.
5. The low power consumption, low noise capacitive MEMS microphone readout circuit of claim 1 wherein the microphone employing said microphone readout circuit employs the following sensor package structure:
the MEMS microphone adopts a bottom hole structure and is directly welded on the PCB;
a sound transmission hole is arranged on the PCB to guide sound into the microphone cavity;
the PCB with the microphone is connected to the external environment;
the PCB, together with the housing constituting the microphone cavity, forms an acoustic circuit element that can influence the frequency response of the microphone.
6. The low power consumption, low noise capacitive MEMS microphone readout circuit of claim 5 wherein said MEMS microphone readout circuit is disposed on a PCB and a microphone aperture is disposed on the PCB for introducing sound into the microphone cavity; a shell is arranged to form the periphery of the microphone cavity;
the microphone cavity formed by the shell is a Helmholtz cavity structure, the cavity structure forms a resonant cavity, and the resonant cavity is connected with the outside through an inner cavity and a sound transmission hole.
7. The low power consumption, low noise capacitive MEMS microphone readout circuit of claim 5 wherein the bottom hole MEMS microphone is directly soldered to said PCB.
8. The low power, low noise capacitive MEMS microphone readout circuit of claim 5 wherein said microphone aperture has a diameter of 0.25mm or greater.
9. The low power, low noise capacitive MEMS microphone readout circuit of claim 6 wherein the resonant frequency of the resonant cavity is calculated according to the formula:
wherein f b Is the resonant frequency; c is sound velocity, 340m/s; d is the diameter of the through hole, and mm; v is the volume of the cavity, mm 3 The method comprises the steps of carrying out a first treatment on the surface of the L is the depth of the cavity, mm.
10. A low power consumption, low noise capacitive MEMS microphone readout circuit according to claim 8, wherein said microphone aperture has a diameter in the range of 0.5mm-1mm.
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| CN202311671863.7A CN117425118A (en) | 2023-12-06 | 2023-12-06 | Low-power-consumption and low-noise capacitive MEMS microphone reading circuit |
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| CN202311671863.7A CN117425118A (en) | 2023-12-06 | 2023-12-06 | Low-power-consumption and low-noise capacitive MEMS microphone reading circuit |
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