CN111431487A - Low-noise microphone preamplifier circuit - Google Patents
Low-noise microphone preamplifier circuit Download PDFInfo
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- CN111431487A CN111431487A CN202010288800.3A CN202010288800A CN111431487A CN 111431487 A CN111431487 A CN 111431487A CN 202010288800 A CN202010288800 A CN 202010288800A CN 111431487 A CN111431487 A CN 111431487A
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- 239000003990 capacitor Substances 0.000 claims abstract description 47
- 230000008878 coupling Effects 0.000 claims abstract description 11
- 238000010168 coupling process Methods 0.000 claims abstract description 11
- 238000005859 coupling reaction Methods 0.000 claims abstract description 11
- 230000003321 amplification Effects 0.000 description 9
- 238000003199 nucleic acid amplification method Methods 0.000 description 9
- 238000005457 optimization Methods 0.000 description 8
- 238000000034 method Methods 0.000 description 6
- 230000035945 sensitivity Effects 0.000 description 6
- 238000010586 diagram Methods 0.000 description 3
- 230000000694 effects Effects 0.000 description 3
- 230000001629 suppression Effects 0.000 description 3
- 230000007547 defect Effects 0.000 description 2
- 238000001914 filtration Methods 0.000 description 2
- 230000008569 process Effects 0.000 description 2
- 230000009286 beneficial effect Effects 0.000 description 1
- 238000006243 chemical reaction Methods 0.000 description 1
- 230000003750 conditioning effect Effects 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
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- 230000004044 response Effects 0.000 description 1
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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
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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
- H03F1/38—Positive-feedback circuit arrangements without negative feedback
Abstract
The invention provides a low-noise microphone preamplifier circuit, wherein an external voltage is filtered by a low-pass filter 1 and then provides a voltage for an electret of a microphone, the external voltage is grounded through a series resistor C, D, a signal input from the electret is filtered into a pure alternating current signal through an alternating current coupling capacitor, a direct current bias is obtained through a connecting node of a series resistor C, D, the signal is input from an equidirectional input end of an operational amplifier, the reverse input end of the operational amplifier is grounded through a low-pass filter 2, a high-pass filter is connected between the reverse input end and the output end of the operational amplifier, and the output end of the operational amplifier is connected with a low-pass filter 3. The invention only needs to adopt a single power supply to supply power, can fully exert the performance of the sensor and has the capability of optimizing the overall performance of the system.
Description
Technical Field
The invention relates to the technical field of amplifiers, in particular to a preamplifier circuit.
Background
Electret microphones are the most commonly used microphones in the market due to their low price. An excellent microphone requires low-noise floor to satisfy high-performance recording in addition to low price. When an electret type acoustic-electric sensor used for designing a microphone works, a bias voltage is needed to be added to realize acoustic-electric conversion, an output signal is weak generally, and if signal conditioning such as amplification is not carried out, the signal is directly transmitted to acquisition equipment and is limited by the bottom noise level of an acquisition system, so that the optimal signal-to-noise ratio of a received signal cannot be obtained.
The existing microphone amplifying circuit adopts discrete components and an operational amplifier 2. The design of an amplifying circuit by adopting discrete components (for example, patent CN201710526570.8) needs passive devices such as resistors or capacitors, and the requirement of the structure on the consistency of the resistors and the capacitors is high in order to ensure the working point of the system. Therefore, in order to guarantee the system performance, the consistency of the elements needs to be screened, and the system cost and the production difficulty are increased. In addition, the structure circuit only uses a high-pass filter to inhibit low-frequency interference, and does not process the interference which is easy to be mixed in an audio frequency section in a high-frequency section, so that the defect exists. The amplifying circuit (for example, patent CN201910143666.5) with the operational amplifier structure has high consistency due to the fact that key elements are integrated inside, and only a small amount of resistors and capacitors are needed outside to realize the amplifying function, so that the amplifier circuit has the advantages of cost and performance. However, the circuit based on the operational amplifier adopts a dual-power supply structure, in order to ensure the system performance, the performance can be exerted only by additionally elaborating positive and negative power supplies, the power supply structure is complex, and the circuit scale is large. In addition, the noise suppression circuit of the circuit only considers low-frequency noise interference singly, does not process high-frequency interference, and does not carry out parameter optimization design aiming at sensor indexes.
Disclosure of Invention
In order to overcome the defects of the prior art, the invention provides the low-noise microphone preamplification circuit, which only needs to adopt a single power supply for power supply, can fully exert the performance of a sensor through the selection of a chip and the optimization design of external passive parameters, and has the capability of optimizing the overall performance of a system.
The technical scheme adopted by the invention for solving the technical problems is as follows: a low-noise microphone preamplifier circuit comprises an alternating-current coupling capacitor, an operational amplifier, a high-pass filter, three low-pass filters and a resistor C, D, wherein an external voltage is filtered by the low-pass filter 1 to provide voltage for an electret of a microphone, the external voltage is grounded through a series resistor C, D, a signal input from the electret is filtered by the alternating-current coupling capacitor to be a pure alternating-current signal, a direct-current bias is obtained through a connecting node of a series resistor C, D, the signal is input from the homodromous input end of the operational amplifier, the reverse input end of the operational amplifier is grounded through the low-pass filter 2, the high-pass filter is connected between the reverse input end and the output end of the operational amplifier, the output end of the operational amplifier is connected with the low-pass filter 3, the signal is filtered by the filter and then is output.
The low-pass filter 1 adopts an RC low-pass filter, and an electret of the microphone is connected with a capacitor of the low-pass filter 1 in parallel.
The operational amplifier selection OPA 376; the low-pass filter 1 is connected in series with a 0.1 muF capacitor by using a 2.2k omega resistor; the low-pass filter 2 is formed by connecting a 1k omega resistor and a 10 mu F capacitor in series; the low-pass filter 3 is connected in series by a 49.9 omega resistor and a 10nF capacitor; the high-pass filter is formed by combining a 5.99k omega resistor and a 1nF capacitor in parallel; the value of the alternating current coupling capacitance is 0.1 muF; the resistors C, D are all set to 100k omega.
The invention has the beneficial effects that: compared with the microphone preamplification circuit shown in fig. 2, which modifies the amplification factor through the adjustable resistor so as to adapt to different types of microphones, the method can optimize parameters in advance according to the sensor parameters without trying to determine the circuit parameters online. Compared with other inventions, the circuit of the invention only needs to adopt a single power supply to supply power, does not need a complex positive and negative power supply, and can meet the requirement of a working power supply by one battery. In addition, the invention can further inhibit low-frequency and high-frequency interference through the optimized design of the band-pass filter, has better noise reduction effect than other inventions, and is simple and easy to apply.
Drawings
Fig. 1 is a schematic diagram of a low noise microphone preamplifier circuit of the present invention.
Fig. 2 is a schematic diagram of a microphone preamplifier circuit of the invention patent application "a microphone preamplifier circuit with gain adjustment" (patent application No. CN 201910143666.5).
Fig. 3 is a schematic diagram of a microphone amplifying circuit of the invention patent application "a microphone amplifying circuit" (patent application No. CN 201710526570.8).
Detailed Description
The present invention will be further described with reference to the following drawings and examples, which include, but are not limited to, the following examples.
The invention provides a low-noise microphone preamplifier circuit which mainly comprises an electret microphone, an alternating-current coupling capacitor, an operational amplifier, high and low-pass filters (low- pass numbers 1, 2 and 3) and a resistor C, D. The applied voltage is filtered by a low-pass filter 1 and then provides a voltage for an electret, wherein the electret is connected with a capacitor H in the low-pass filter 1 in parallel. The applied voltage is connected with the series resistor C, D and then grounded, a signal input from the electret is filtered into a pure alternating current signal through the alternating current coupling capacitor, and then the signal is input from the same-direction input end of the operational amplifier after the direct current bias is obtained through the connection node of the series resistor C, D. The reverse input end of the operational amplifier is connected with the low-pass filter 2, the high-pass filter is connected between the reverse input end and the output end, the output end is connected with the low-pass filter 3, signal noise is filtered by the band-pass filter and then is output from the output end of the operational amplifier, and finally, the signal noise is filtered by the low-pass filter 3 and then is output.
The invention adopts the following optimized design:
(I) Circuit optimization
The operational amplifier circuit used at present is constructed by adopting a positive power supply and a negative power supply, and in order to realize high fidelity of signals, a large-scale noise suppression circuit is needed to filter the power supply to reduce noise, so that the circuit scale and the cost are increased. Aiming at the problem, the invention innovatively uses a single power supply mode, adopts a band-pass filter to further inhibit low-frequency and high-frequency interference, does not need an additional set of negative power generator and noise suppression circuit on the premise of ensuring the performance, reduces the circuit scale and can effectively reduce the cost on the premise of ensuring the performance.
(II) type selection optimization
The invention gives a corresponding parameter optimization method by taking an electret microphone with a specific model as an example, and when the method is actually applied, the corresponding resistor and capacitor can be modified according to the sensitivity and the signal-to-noise ratio of the actually adopted sensor to realize relatively optimal performance.
For electret microphones on the market, an EM189T type acoustoelectric sensor is selected for design, the signal-to-noise ratio of the sensor is 68dB, the sensitivity is-43 dBV (94dB L), and the output impedance is 2.2k omega.
Because the standard recording file signal range is changed between-1V- +1V, and when the sensor does not amplify, the sensitivity at full-range input of 120dB L is-17 dBV, therefore, in order to ensure that the signal at full-range input does not exceed-1V- +1V, the pick-and-place large factor is 17dB, namely 1017/20 is approximately 7 times.
Considering that the performance of the sensor is played as much as possible, the noise of the amplifying circuit needs to be extremely low, the main noise source of the amplifying circuit is an operational amplifier, and the system performance can be optimized through the optimization of the parameters of an external passive device only by selecting a proper operational amplifier. Because the output impedance of the selected sensor is 2.2k Ω, the selected operational amplifier must have high input impedance to reduce the influence of inaccurate amplification factor caused by attenuation of the sensor signal by the operational amplifier as a load, and for the above requirement, the present invention selects the OPA376 as the operational amplifier of the circuit, the voltage noise of the OPA376 is 7.5nV/√ Hz, and the input impedance is much larger than 2.2k Ω.
As the signal range of the human voice is 20 Hz-20 kHz, the amplifier circuit has flat response in the frequency band to ensure high-fidelity recording effect, and the allowed bandwidth of the amplifier circuit is set to cover 20 Hz-20 kHz.
The output noise of the amplifying circuit is composed of the background noise of the operational amplifier and the thermal noise of the resistor, and the thermal noise of the resistor is gradually increased along with the increase of the resistance value. Since the amplification factor of the same-direction amplifier is related to the resistors E and F, the specific amplification factor is (1+ RF/RE) ═ 7. The proportion is unchanged, the larger the two resistance values are, the larger the introduced thermal noise is, and the resistance is selected to be too small, so that the thermal noise of the resistance can be reduced, but the system power consumption is also increased, and a larger capacitor is also needed to restrict the bandwidth of the circuit to be 20 Hz-20 kHz. Therefore, when the external resistor has an amplification factor of 7, it is necessary to select RE equal to 1k Ω and RF equal to 5.99k Ω in consideration of factors such as power consumption of the system, thermal noise of the resistor, and specifications of a common resistor in the market.
The low pass filter 1 uses a combination of a 2.2k omega resistor in series with a 0.1 muf capacitor for filtering high frequency noise from the power supply at >723 Hz.
The capacitance alternating current coupling I is 0.1 muF, the capacitance value can effectively isolate direct current flowing through, only alternating current signals of more than 31Hz can be allowed to pass through, and the condition that approximately pure alternating current signals are supplied to the positive end of the operational amplifier is ensured. Resistors C, D are all set to 100k Ω so the circuit branch current is dc and the dc voltage at node 4 is 1.65V. The current drawn by the operational amplifier is therefore dc biased.
The low pass filter 2 is made up of a series combination of a 1k omega resistor and a 10 muf capacitor, allowing only ac signals <16Hz to pass. The high pass filter is combined by a 5.99k Ω resistor in parallel with a 1nF capacitor, allowing only ac signals >26570Hz to pass. The high-pass filter and the low-pass filter 2 are combined into a band-pass filter, and signals of 20 Hz-20 kHz are fully reserved.
The low pass filter 3 consists of a 49.9 Ω resistor in series with a 10nF capacitor, allowing only ac signals <328947Hz to pass. The low-pass filter 3 is used for filtering out external radio frequency interference.
The main source of the internal noise of the circuit is the operational amplifier, the total RMS noise of the operational amplifier is 120.7 muV, and the optimization effect is obvious.
As shown in FIG. 1, in the present invention, the microphone preamplifier circuit includes an electret microphone A (model EM189T), circuit resistances B (2.2K Ω), C (100K Ω), D (100K Ω), E (1K Ω), F (5.99K Ω), G (49.9 Ω), circuit capacitances H (0.1 μ F), I (0.1 μ F), J (10 μ F), K (1nF), L (10nF), and an operational amplifier M (model OPA 376).
The invention selects an EM189T model acoustoelectric sensor of Primo company for design, the signal-to-noise ratio of the sensor is 68dB, the sensitivity is-43 dBV (94dB L), the output impedance is 2.2k omega, when the sensor is not amplified, the sensitivity is-43 dBV +26 dBV-17 dBV when 120dB L full range is input, therefore, in order to ensure that the signal does not exceed-1V- +1V when the full range is input, the picking and placing times are 17dB, namely 10 dB17/207 times.
The invention selects the OPA376 as a circuit operational amplifier, the voltage noise of the OPA376 is 7.5 nV/V Hz, and the input impedance is far larger than 2.2k omega.
The additional +3.3V voltage is connected to the ① end of the resistor B, the ② end of the resistor B is connected to the capacitor H, the other end of the capacitor H is grounded, the electret A and the electret H are connected in parallel, and the additional +3.3V voltage provides voltage for the electret A to convert the sound signal of the electret A into an electric signal to be input into the circuit.
Because the external power supply has noise, the resistor B and the capacitor H are connected in series to form a low-pass filter 1, so that the noise of the power supply is filtered, and a stable and low-noise power supply is provided for the electret A.
One end of the resistor C is connected with the end ①, the end ④ of the resistor C is connected with the end ④ of the resistor D, and the other end of the resistor D is grounded, wherein the anode of the electret A is connected with the capacitor I, the other end of the capacitor I is connected with the end ④ of the resistor C, the capacitor I is an alternating current coupling capacitor and is used for isolating direct current flowing through the capacitor I and only allowing alternating current signals to pass, and the signals provided for the non-inverting input end of the operational amplifier M are pure alternating current signals.
The resistor C, D is analyzed according to ohm's law, and the circuit passing through the resistor C, D is a direct current, so that the direct current bias of the operational amplifier M is 1.65V according to kirchhoff's law.
The positive pole of the power supply of the operational amplifier M is added with +3.3V voltage, and the negative pole is grounded.
The operational amplifier M is characterized in that the reverse input end of the operational amplifier M is connected to the ⑧ end of the resistor E, the other end of the resistor E is connected to the capacitor J, the other end of the capacitor J is grounded, the resistor E and the capacitor J are connected in series to form a low-pass filter 2, high-frequency noise of a power supply is filtered, and an electric signal with low noise is obtained.
The output end of the operational amplifier M is connected to the ⑥ end of the resistor G, the other end of the resistor G is connected to the capacitor L, the other end of the capacitor L is grounded, the resistor G and the capacitor L are connected in series to form a low-pass filter 3, and radio frequency interference in the circuit is filtered to obtain an output end electric signal with low noise.
On the feedback circuit of the operational amplifier M, one end of the resistor F is connected with the resistor G, and the other end of the resistor F is connected with the resistor E. The capacitor K is connected with the resistor F in parallel. The resistor F and the capacitor K are connected in parallel to form a high-pass filter, low-frequency noise of the power supply is filtered, and a low-noise electric signal is obtained.
The high-pass filter formed by connecting the resistor F and the capacitor K in parallel and the low-pass filter 2 formed by connecting the resistor E and the capacitor J in series on the reverse input end jointly act to form the band-pass filter.
The operational amplifier M here constitutes an in-phase proportional operational circuit, which is used to amplify the electrical signal inputted from the in-phase input terminal, and the amplification factor is related to the reverse input terminal resistance E and the feedback circuit resistance F, specifically the amplification factor is (1+ RF/RE), and in the present invention, the amplification factor is 7.
The electric signal is output from the low-pass filter (resistor G and capacitor L) at the output end of the operational amplifier M, and is converted into an acoustic signal by a subsequent unit for output.
The above-mentioned embodiments only provide the corresponding parameter optimization method for the electret microphone of the preferred model of the present invention, and do not limit the concept and scope of the present invention. In practical application, the corresponding resistor and capacitor can be modified according to the sensitivity and signal-to-noise ratio of the sensor actually adopted to realize relatively optimal performance, so that various modifications and improvements made to the technical scheme of the invention by ordinary persons in the art all fall into the protection scope of the invention.
Claims (3)
1. A low-noise microphone preamplifier circuit comprises an alternating current coupling capacitor, an operational amplifier, a high-pass filter, three low-pass filters and a resistor C, D, and is characterized in that: the applied voltage is filtered by the low-pass filter 1 to provide voltage for the electret of the microphone, the applied voltage is grounded through the series resistor C, D, a signal input from the electret is filtered into a pure alternating current signal through the alternating current coupling capacitor, a direct current bias is obtained through a connecting node of the series resistor C, D, the signal is input from the same-direction input end of the operational amplifier, the reverse input end of the operational amplifier is grounded through the low-pass filter 2, the high-pass filter is connected between the reverse input end and the output end of the operational amplifier, the output end of the operational amplifier is connected with the low-pass filter 3, the signal is filtered by the filter and then output from the output end of the operational amplifier, and finally.
2. A low noise microphone preamplifier circuit according to claim 1, wherein: the low-pass filter 1 adopts an RC low-pass filter, and an electret of the microphone is connected with a capacitor of the low-pass filter 1 in parallel.
3. A low noise microphone preamplifier circuit according to claim 1, wherein: the operational amplifier selection OPA 376; the low-pass filter 1 is connected in series with a 0.1 muF capacitor by using a 2.2k omega resistor; the low-pass filter 2 is formed by connecting a 1k omega resistor and a 10 mu F capacitor in series; the low-pass filter 3 is connected in series by a 49.9 omega resistor and a 10nF capacitor; the high-pass filter is formed by combining a 5.99k omega resistor and a 1nF capacitor in parallel; the value of the alternating current coupling capacitance is 0.1 muF; the resistors C, D are all set to 100k omega.
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| Application Number | Priority Date | Filing Date | Title |
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| CN202010288800.3A CN111431487A (en) | 2020-04-14 | 2020-04-14 | Low-noise microphone preamplifier circuit |
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| CN202010288800.3A CN111431487A (en) | 2020-04-14 | 2020-04-14 | Low-noise microphone preamplifier circuit |
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN112305329A (en) * | 2020-10-29 | 2021-02-02 | 北京航空航天大学 | Device and method for detecting state of component based on low-frequency noise |
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| CN1868114A (en) * | 2003-10-14 | 2006-11-22 | 音频专用集成电路公司 | Microphone preamplifier |
| CN103997303A (en) * | 2014-05-13 | 2014-08-20 | 北京燕东微电子有限公司 | High-gain pre-amplifier for electret microphone and electret microphone |
| CN203942499U (en) * | 2014-05-13 | 2014-11-12 | 北京燕东微电子有限公司 | For high-gain preamplifier and the electret microphone of electret microphone |
| CN205051656U (en) * | 2015-11-03 | 2016-02-24 | 歌尔声学股份有限公司 | Microphone amplification circuit |
| CN105848055A (en) * | 2016-03-29 | 2016-08-10 | 华南理工大学 | Microphone circuit used for electronic stethoscope |
| CN107071651A (en) * | 2017-06-30 | 2017-08-18 | 湖州灵感电子科技有限公司 | A kind of microphone amplifying circuit |
| CN206674176U (en) * | 2017-04-12 | 2017-11-24 | 深圳普创天信科技发展有限公司 | A kind of microphone denoising amplifying circuit of intelligent sound equipment |
| CN109831719A (en) * | 2019-02-26 | 2019-05-31 | 深圳市美恩微电子有限公司 | A kind of microphone preamplifier circuit trimmed with gain |
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2020
- 2020-04-14 CN CN202010288800.3A patent/CN111431487A/en active Pending
Patent Citations (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN1868114A (en) * | 2003-10-14 | 2006-11-22 | 音频专用集成电路公司 | Microphone preamplifier |
| CN103997303A (en) * | 2014-05-13 | 2014-08-20 | 北京燕东微电子有限公司 | High-gain pre-amplifier for electret microphone and electret microphone |
| CN203942499U (en) * | 2014-05-13 | 2014-11-12 | 北京燕东微电子有限公司 | For high-gain preamplifier and the electret microphone of electret microphone |
| CN205051656U (en) * | 2015-11-03 | 2016-02-24 | 歌尔声学股份有限公司 | Microphone amplification circuit |
| CN105848055A (en) * | 2016-03-29 | 2016-08-10 | 华南理工大学 | Microphone circuit used for electronic stethoscope |
| CN206674176U (en) * | 2017-04-12 | 2017-11-24 | 深圳普创天信科技发展有限公司 | A kind of microphone denoising amplifying circuit of intelligent sound equipment |
| CN107071651A (en) * | 2017-06-30 | 2017-08-18 | 湖州灵感电子科技有限公司 | A kind of microphone amplifying circuit |
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
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| CN112305329A (en) * | 2020-10-29 | 2021-02-02 | 北京航空航天大学 | Device and method for detecting state of component based on low-frequency noise |
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