CN113194389A - Power supply noise reduction circuit and system - Google Patents

Power supply noise reduction circuit and system Download PDF

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Publication number
CN113194389A
CN113194389A CN202110472601.2A CN202110472601A CN113194389A CN 113194389 A CN113194389 A CN 113194389A CN 202110472601 A CN202110472601 A CN 202110472601A CN 113194389 A CN113194389 A CN 113194389A
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power supply
transistor
capacitor
noise reduction
resistor
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宋源
郭晓东
赵明明
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Sichuan Hongmei Intelligent Technology Co Ltd
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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
    • H04R3/00—Circuits for transducers, loudspeakers or microphones
    • H04R3/04—Circuits for transducers, loudspeakers or microphones for correcting frequency response
    • H04R3/06—Circuits for transducers, loudspeakers or microphones for correcting frequency response of electrostatic transducers
    • 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
    • H04R19/01—Electrostatic transducers characterised by the use of electrets
    • H04R19/016—Electrostatic transducers characterised by the use of electrets for microphones

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  • Engineering & Computer Science (AREA)
  • Acoustics & Sound (AREA)
  • Signal Processing (AREA)
  • Amplifiers (AREA)

Abstract

The invention provides a power supply noise reduction circuit and a system, wherein the power supply noise reduction circuit comprises: a filter circuit and a load; the filter circuit includes: an RC filter circuit and a transistor; the RC filter circuit includes: a first resistor and a first capacitor; the first end of the first resistor is connected with the power supply input end, the second end of the first resistor is connected with the first end of the first capacitor, the second end of the first capacitor is connected with the ground wire, the collector electrode of the transistor is connected with the first end of the first resistor, the base stage of the transistor is connected with the first end of the first capacitor, the emitter electrode of the transistor is connected with the voltage output end, the first end of the load is connected with the emitter electrode of the transistor, and the second end of the load is connected with the ground wire; a transistor for increasing a capacitance value of the equivalent capacitance by using a current amplification characteristic thereof; the equivalent capacitance is used for representing the equivalent capacitance of a circuit formed by the first resistor, the first capacitor and the transistor. This scheme can improve the noise reduction of power.

Description

Power supply noise reduction circuit and system
Technical Field
The invention relates to the technical field of electrical engineering, in particular to a power supply noise reduction circuit and system.
Background
Household electrical appliances with voice recognition function, such as refrigerators, air conditioners, etc., have to use electret microphones with long leads due to their own structural limitations. However, the signal line is too long, which causes the line to be easily interfered, and once other noises are introduced to the microphone, the sound pickup effect of the microphone is seriously affected, and the voice recognition rate is also greatly reduced. Thus, the electret microphone has very high requirements on its power supply ripple and noise.
At present, for the power supply design of a microphone, a general scheme is to use a low dropout regulator LDO with a higher ripple noise rejection ratio PSRR to implement the power supply design. However, the LDO with a higher PSRR has a larger package and a higher cost, and is not an optimal way for reducing noise of a microphone power supply because of a general noise reduction effect on the microphone power supply.
Therefore, it is desirable to provide a solution that can improve the noise reduction effect of the power supply.
Disclosure of Invention
The invention provides a power supply noise reduction circuit and a system, which can improve the noise reduction effect of a power supply.
In a first aspect, an embodiment of the present invention provides a power supply noise reduction circuit, including: a filter circuit and a load;
the filter circuit includes: an RC filter circuit and a transistor;
the RC filter circuit comprises: a first resistor and a first capacitor;
the first end of the first resistor is connected with a power supply input end, the second end of the first resistor is connected with the first end of the first capacitor, the second end of the first capacitor is connected with a ground wire, the collector electrode of the transistor is connected with the first end of the first resistor, the base stage of the transistor is connected with the first end of the first capacitor, the emitter electrode of the transistor is connected with a voltage output end, the first end of the load is connected with the emitter electrode of the transistor, and the second end of the load is connected with the ground wire;
the RC filter circuit is used for filtering noise of the input voltage of the power supply input end;
the transistor is used for increasing the capacitance value of the equivalent capacitor by utilizing the current amplification characteristic of the transistor so as to improve the performance of the RC filter circuit for filtering the noise of the input voltage; wherein the equivalent capacitance is used for characterizing the equivalent capacitance of a circuit formed by the first resistor, the first capacitor and the transistor.
In one possible implementation manner, the power supply noise reduction circuit further includes: a second capacitor;
the first end of the second capacitor is connected with the emitter of the transistor, and the second end of the second capacitor is connected with the ground wire;
and the second capacitor is used for filtering alternating current components in the voltage output by the filter circuit so as to enable the output direct current voltage to be smoother.
In one possible implementation, the capacitance value of the first capacitor is calculated by the following formula:
Figure BDA0003045929920000021
c is used for representing the capacitance value of the first capacitor, f is used for representing the cut-off frequency of the filter circuit, R is used for representing the resistance value of the first resistor, and pi is 3.1415926.
In one possible implementation, the transistor is an NPN transistor.
In one possible implementation, the transistor is packaged in an SOT-723 package.
In a second aspect, an embodiment of the present invention further provides a power supply noise reduction system, where the system includes: a power supply module, the power supply noise reduction circuit, the parameter adjustment module and the load module according to any of the embodiments of the first aspect;
the power supply module is electrically connected with the power supply noise reduction circuit;
the parameter adjusting module is connected with the power supply noise reduction circuit;
the power supply module is used for providing a voltage source for the power supply noise reduction circuit and the load module;
the parameter adjusting module is used for judging whether the parameters of each element in the power supply noise reduction circuit meet the preset specification requirements of the power supply noise reduction circuit or not and outputting the parameters of each element when the parameters meet the specification requirements; and generating a prompt signal indicating that the parameter is deviated when the parameter is not satisfied.
According to the technical scheme, the power supply noise reduction circuit provided by the invention is different from the traditional noise reduction circuit, except for the traditional RC filter circuit, the scheme is characterized in that a transistor is added, and the first resistor is used as a base bias resistor of the transistor, namely, the second end of the first resistor is connected with the base of the transistor. In the circuit, the first resistor and the first capacitor form a section of RC filter circuit, and the first resistor not only provides base bias current for the transistor, but also is a filter resistor. The current flowing through the first resistor is the base bias current of the transistor, and the current is very small, so that the resistance value of the first resistor can be relatively large, the RC filter circuit formed by the first resistor and the first capacitor has a better effect, and the current component in the direct current voltage on the base of the transistor is less. Because the emitter voltage has the characteristic of following the base voltage, the alternating current component in the output voltage of the emitter of the transistor is less, and the aim of improving filtering and noise reduction is fulfilled.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to these drawings without creative efforts.
FIG. 1 is a circuit diagram of a power supply noise reduction circuit according to an embodiment of the present invention;
FIG. 2 is a circuit diagram of a power supply noise reduction circuit according to another embodiment of the present invention;
FIG. 3 is a schematic diagram of a test of a power supply system for a microphone bias power supply according to an embodiment of the present invention;
fig. 4 is a schematic diagram of a power supply noise reduction system according to an embodiment of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer and more complete, the technical solutions in the embodiments of the present invention will be described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all, embodiments of the present invention, and based on the embodiments of the present invention, all other embodiments obtained by a person of ordinary skill in the art without creative efforts belong to the scope of the present invention.
As shown in fig. 1, an embodiment of the present invention provides a power supply noise reduction circuit, including: a filter circuit and a load RL;
a filter circuit, comprising: an RC filter circuit and transistor Q1;
an RC filter circuit comprising: a first resistor R1 and a first capacitor C1;
a first end of a first resistor R1 is connected with a power supply input end, a second end of a first resistor R1 is connected with a first end of a first capacitor C1, a second end of the first capacitor C1 is connected with a ground wire, a collector of a transistor Q1 is connected with a first end of a first resistor R1, a base of a transistor Q1 is connected with a first end of a first capacitor C1, an emitter of the transistor Q1 is connected with a voltage output end, a first end of a load RL is connected with an emitter of a transistor Q1, and a second end of the load RL is connected with the ground wire;
the RC filter circuit is used for filtering noise of input voltage at the input end of the power supply;
the transistor Q1 is used for increasing the capacitance value of the equivalent capacitor by utilizing the current amplification characteristic of the transistor Q1 so as to improve the performance of the RC filter circuit for filtering the noise of the input voltage; the equivalent capacitance is used for representing the equivalent capacitance of a circuit formed by the first resistor R1, the first capacitor C1 and the transistor Q1.
In the embodiment of the invention, the provided power supply noise reduction circuit is different from a traditional noise reduction circuit, except for a traditional RC filter circuit, the scheme focuses on adding a transistor, and a first resistor is used as a base bias resistor of the transistor, namely, a second end of the first resistor is connected with the base of the transistor. In the circuit, the first resistor and the first capacitor form a section of RC filter circuit, and the first resistor not only provides base bias current for the transistor, but also is a filter resistor. The current flowing through the first resistor is the base bias current of the transistor, and the current is very small, so that the resistance value of the first resistor can be relatively large, the RC filter circuit formed by the first resistor and the first capacitor has a better effect, and the current component in the direct current voltage on the base of the transistor is less. Because the emitter voltage has the characteristic of following the base voltage, the alternating current component in the output voltage of the emitter of the transistor is less, and the aim of improving filtering and noise reduction is fulfilled.
In the embodiment of the invention, the transistor Q1 plays the role of a filter tube; the first capacitor C1 is a base filter capacitor; the first resistor R1 is the base bias resistor of the transistor Q1; RL is the load (e.g., microphone, etc.) for this filtering noise reduction. The transistor Q1, the first resistor R1 and the first capacitor C1 in the circuit form an electronic filter circuit, the circuit is equivalent to a capacitor with the capacity of C1 × β, and β is the current amplification factor of the transistor Q1, so that the capacity of an equivalent capacitor can be increased by selecting the transistor Q1 with higher current amplification factor, and the performance of the electronic filter is improved.
It should be noted that the filtering of the noise reduction circuit provided by the present disclosure is mainly implemented by the first resistor R1 and the first capacitor C1, which is also an RC filter circuit. However, it is different from the conventional RC filter circuit in that the dc current flowing through the load in this circuit is the emitter current of the transistor Q1, the current flowing through the first resistor R1 (i.e. the filter resistor) is the base current of the transistor Q1, and the base current is very small, so that the resistance value of the filter resistor can be set very large (good filtering effect) without greatly reducing the dc output voltage.
For example, a conventional household appliance has a high voltage ac 220V and a low voltage dc 12V. The device comprises a compressor, an electric control board, an infrared receiving unit, a sensor unit and the like. In such a complicated electromagnetic environment, the addition of the voice recognition function requires noise reduction and filtering of the power supply of the voice recognition portion, taking the power supply of a microphone as an example for noise reduction.
1. The 12V direct current output on the electric control board of the household appliance is converted into a 3.3V direct current power supply through the voltage reduction treatment of the switching power supply. Since a 3.3V dc power supply is more suitable for the power input of the electronic filter, i.e. VIN in fig. 1;
2. the 3.3V direct-current power supply charges C1 through R1, and meanwhile, R1 and C1 form an RC filter circuit for filtering high-frequency noise carried in the power supply;
3. as the voltage of the capacitor C1 becomes higher, the voltage of VOUT becomes higher; up to VIN minus the pipe drop.
4. Since the transistor Q1 works in the amplifying state, its maximum current amplification factor is β, thus forming a larger capacitor of C1 × β with C1, so as to achieve better filtering, noise reduction and voltage stabilization effects.
Through the design, the microphone signal in the voice recognition unit can be very good, so that the microphone can still clearly transmit the audio signal in a complex electromagnetic environment and a power supply environment, and the improvement of the voice recognition rate is facilitated.
In a possible implementation manner, as shown in fig. 2, the power supply noise reduction circuit may further include: a second capacitance C2;
a first end of the second capacitor C2 is connected with the emitter of the transistor Q1, and a second end of the second capacitor C2 is connected with the ground line;
and the second capacitor C2 is used for filtering out alternating current components in the voltage output by the filter circuit so as to make the output direct current voltage smoother.
In the embodiment of the invention, a second capacitor C2 is added at one end of an emitter of the transistor Q1, the second capacitor C2 is a filter capacitor of the output voltage, and an alternating current component in the output voltage is filtered by the filter capacitor, so that the output direct current voltage is smoother, and the output performance of the power supply noise reduction circuit is improved.
In a possible implementation manner, the capacitance value of the first capacitor C1 in the power supply noise reduction circuit may be calculated by considering the following formula:
Figure BDA0003045929920000061
wherein, C is used for representing the capacitance value of the first capacitor C1, f is used for representing the cut-off frequency of the filter circuit, R is used for representing the resistance value of the first resistor R1, and pi is 3.1415926.
In the embodiment of the present invention, a specific determination manner of the first capacitor C1 (i.e., the fundamental filter capacitor) is given, and the parameters involved in the formula include the first resistor R1 and the cutoff frequency. Therefore, the proper capacitance value can be set and adjusted according to different application scenes, namely the noise intensity under different scenes, so that the applicability of the noise reduction circuit is improved.
For example, signals higher than 140Hz need to be suppressed, and the given resistance value of the first resistor R1 is 100 Ω, so that the capacitance value of the first capacitor C1 is 1/(2 × pi × 100 × 140) ═ 11 μ F, and thus, in practical application, the cutoff frequency is obtained according to different noise decibel values, and the value of the first capacitor C1 can be accurately calculated, thereby ensuring the accuracy of filtering the specific frequency wave.
In one possible implementation, the transistor Q1 is an NPN transistor.
In addition, the packaging of the transistor Q1 can also be considered in the form of SOT-723 packaging. Because the traditional scheme for reducing the noise of the microphone power supply is realized by adopting the low dropout regulator LDO with the ripple noise rejection ratio (PSRR) higher, the PSRR is usually more than 70dB to achieve a good noise reduction effect, the package of the LDO is usually SOT23-5, the standard package size of SOT23-5 is 2.9 x 2.8mm, and the price is also in the order of a few gross money. According to the scheme for reducing the noise of the power supply, a common NPN transistor Q1 is packaged into an SOT-723, the standard packaging size of the NPN transistor Q1 is 1.2 x 1.2mm, the price is in the order of several cents, the occupied area of a PCB can be reduced, and the cost is lower.
The advantages of the scheme of the present invention are further illustrated by a specific example compared to the LDO scheme.
In the LDO scheme, the model of the LDO adopts SGM2032, the package of the SGM is SOT23-5, and the PSRR is 75db @1 KHz. The NPN transistor Q1 is L2SC5658 commonly used by radio and is packaged as an NPN transistor of SOT-723. The two schemes are respectively used as bias power supplies of the microphones. A system test block diagram is shown in fig. 3.
By placing the above system in an environment with noise below 20dB, the PC side is equipped with audio analysis software Audacity. The microphone transmits the picked environmental noise back to the voice chip, and the voice chip transmits the voice signal to Audacity software at the PC end through the USB bus. Audacity software is used for analyzing frequency spectrums of audio signals picked up by the microphone under different power supply schemes. The comparison analysis result shows that the microphone signal with the LDO as the bias power supply has obvious noise interference. When the electronic filter composed of the NPN transistor Q1 is used as the bias power supply of the microphone, the microphone signal obtained in the spectrum analysis is very clean.
As shown in fig. 4, an embodiment of the present invention further provides a power supply noise reduction system, including: the power supply comprises a power supply module, a power supply noise reduction circuit, a parameter adjusting module and a load module in any embodiment;
the power supply module is electrically connected with the power supply noise reduction circuit;
the parameter adjusting module is connected with the power supply noise reduction circuit;
the power supply module is used for providing a voltage source for the power supply noise reduction circuit and the load module;
the parameter adjusting module is used for judging whether the parameters of each element in the power supply noise reduction circuit meet the preset specification requirements of the power supply noise reduction circuit or not and outputting the parameters of each element when the parameters meet the specification requirements; and generating a prompt signal indicating that the parameter is deviated when the parameter is not satisfied.
In the embodiment of the invention, the power supply module in the power supply noise reduction system is used for providing a voltage source for the system, and the parameter adjusting module is connected with the power supply noise reduction circuit to detect whether the parameters of each component in the circuit meet the preset voltage output standard or not, so that the system not only can filter the power supply noise, but also can be set according to the actual requirement to ensure that the performance of the output voltage reaches the specific standard.
In summary, the power supply noise reduction circuit and system provided by the embodiments of the invention at least have the following beneficial effects:
1. in the embodiment of the invention, the provided power supply noise reduction circuit is different from a traditional noise reduction circuit, except for a traditional RC filter circuit, the scheme focuses on adding a transistor, and a first resistor is used as a base bias resistor of the transistor, namely, a second end of the first resistor is connected with the base of the transistor. In the circuit, the first resistor and the first capacitor form a section of RC filter circuit, and the first resistor not only provides base bias current for the transistor, but also is a filter resistor. And because the base bias current of the transistor when the current flows through the first resistor is very small, the resistance value of the first resistor can be relatively large, so that the RC filter circuit formed by the first resistor and the first capacitor has a good effect, and the current component in the direct current voltage on the base of the transistor is very small. Because the emitter voltage has the characteristic of following the base voltage, the alternating current component in the output voltage of the emitter of the transistor is less, and the purpose of filtering and noise reduction is improved.
2. In the embodiment of the invention, a second capacitor is added at one end of the emitter of the transistor, the second capacitor is a filter capacitor of the output voltage, and the alternating current component in the output voltage is filtered by the filter capacitor, so that the output direct current voltage is smoother, and the output performance of the power supply noise reduction circuit is improved.
3. In the embodiment of the present invention, a specific determination manner of the first capacitor (i.e., the fundamental filter capacitor) is given, and the parameters involved in the formula include the first resistor and the cut-off frequency. Therefore, the proper capacitance value can be set and adjusted according to different application scenes, namely the noise intensity under different scenes, so that the applicability of the noise reduction circuit is improved.
4. Because the traditional scheme for reducing the noise of the microphone power supply is realized by adopting the low dropout regulator LDO with the ripple noise rejection ratio (PSRR) higher, the PSRR is usually more than 70dB to achieve a good noise reduction effect, the package of the LDO is usually SOT23-5, the standard package size of SOT23-5 is 2.9 x 2.8mm, and the price is also in the order of a few gross money. According to the scheme for reducing the noise of the power supply, a common NPN transistor is packaged into the SOT-723, the standard packaging size of the NPN transistor is 1.2 x 1.2mm, the price is in the order of several cents, the occupied area of a PCB can be reduced, and the cost is lower.
It is noted that, herein, relational terms such as first and second, and the like may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Also, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising a" does not exclude the presence of other similar elements in a process, method, article, or apparatus that comprises the element.
Finally, it is to be noted that: the above description is only a preferred embodiment of the present invention, and is only used to illustrate the technical solutions of the present invention, and not to limit the protection scope of the present invention. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention shall fall within the protection scope of the present invention.

Claims (6)

1. A power supply noise reduction circuit, comprising: a filter circuit and a load;
the filter circuit includes: an RC filter circuit and a transistor;
the RC filter circuit comprises: a first resistor and a first capacitor;
the first end of the first resistor is connected with a power supply input end, the second end of the first resistor is connected with the first end of the first capacitor, the second end of the first capacitor is connected with a ground wire, the collector electrode of the transistor is connected with the first end of the first resistor, the base stage of the transistor is connected with the first end of the first capacitor, the emitter electrode of the transistor is connected with a voltage output end, the first end of the load is connected with the emitter electrode of the transistor, and the second end of the load is connected with the ground wire;
the RC filter circuit is used for filtering noise of the input voltage of the power supply input end;
the transistor is used for increasing the capacitance value of the equivalent capacitor by utilizing the current amplification characteristic of the transistor so as to improve the performance of the RC filter circuit for filtering the noise of the input voltage; wherein the equivalent capacitance is used for characterizing the equivalent capacitance of a circuit formed by the first resistor, the first capacitor and the transistor.
2. The power supply noise reduction circuit of claim 1, further comprising: a second capacitor;
the first end of the second capacitor is connected with the emitter of the transistor, and the second end of the second capacitor is connected with the ground wire;
and the second capacitor is used for filtering alternating current components in the voltage output by the filter circuit so as to enable the output direct current voltage to be smoother.
3. The power supply noise reduction circuit according to claim 1, wherein the capacitance value of the first capacitor is calculated by the following formula:
Figure FDA0003045929910000011
c is used for representing the capacitance value of the first capacitor, f is used for representing the cut-off frequency of the filter circuit, R is used for representing the resistance value of the first resistor, and pi is 3.1415926.
4. The power supply noise reduction circuit according to claim 1, wherein the transistor is an NPN transistor.
5. The power supply noise reduction circuit according to claim 4, wherein the package of the transistor is an SOT-723 package.
6. A power supply noise reduction system, comprising: a power supply module, the power supply noise reduction circuit of any one of claims 1 to 5, a parameter adjustment module and a load module;
the power supply module is electrically connected with the power supply noise reduction circuit;
the parameter adjusting module is connected with the power supply noise reduction circuit;
the power supply module is used for providing a voltage source for the power supply noise reduction circuit and the load module;
the parameter adjusting module is used for judging whether the parameters of each element in the power supply noise reduction circuit meet the preset specification requirements of the power supply noise reduction circuit or not and outputting the parameters of each element when the parameters meet the specification requirements; and generating a prompt signal indicating that the parameter is deviated when the parameter is not satisfied.
CN202110472601.2A 2021-04-29 2021-04-29 Power supply noise reduction circuit and system Pending CN113194389A (en)

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