CN1290114A

CN1290114A - Microphone circuit with high noise resistance

Info

Publication number: CN1290114A
Application number: CN 99117114
Authority: CN
Inventors: 苏明
Original assignee: Individual
Current assignee: Individual
Priority date: 1999-09-27
Filing date: 1999-09-27
Publication date: 2001-04-04

Abstract

A microphone circuit with high noise resistance especially for the speech recognizing telephone features that two electret microphones are used, which can receive two noise signal with same sound intensity and two speech signals with different intensities. Said noise signals can be fully cancelled but said speech signals are not, so outputting clear sound signals.

Description

A kind of microphone circuit with high noise resistance

The present invention relates to the anti-noise microphone of communication with the microphone, particularly voice identification telephone set of telephone set.

At present, the microphone of relevant ordinary telephone set is not owing to establish the anti-noise device, place them the environment of noise to use so, be difficult to obtain sound clearly, if noise intensity surpasses certain limit, they just can't operate as normal so, causes many inconvenience to people; The microphone of relevant voice identification telephone set, although what have is provided with the anti-noise device, if equally they are placed the noise circumstance of varying strength, so, what have can not correctly respond, and what have can not correctly carry out work by the program of appointment, if noise intensity surpasses certain limit, they just can't operate as normal, has that discrimination is low, anti-noise ability is not enough; Adopt general electret microphone audio input circuit, exist sound and ambient noise to import audio frequency apparatus simultaneously, can not suppress ambient noise; Therefore, the shortcoming that all has poor reliability.

To be solved by this invention is the anti-noise problem of telephone set microphone, from now on telephone set microphone is in the different noise circumstances also can operate as normal, have and only allow the sound input, suppress ambient noise, and directly alternative former MIC connected mode, need not to revise the original equipment circuit, or the anti-noise microphone circuit of external accessory power supply, the internal circuit power supply used; Emphasis of the present invention is to adopt two microphones and current source Q, utilizes two opposite principles that signal is cancelled each other of phase place, but reaches the effect that subtracts even eliminate noise to greatest extent.

The present invention adopts two electret microphone M1, M2; The positive polarity output terminal of M1 is connected in the contact B between load resistance R2 and the output coupling capacitance C2, the negative polarity output head grounding, C2 and the base stage that is connected to current source Q after current-limiting resistance R3 connects, the potential change amount that C2, R3 are ordered B is coupled to the base stage of Q, for the B point, Q is the common emitter current amplifier, with the anti-phase amplification of its output signal; Audio output coupling capacitance C4, isolation resistance R1 connect with filter capacitor C1, another termination audio frequency output of C4, C1 other end ground connection; The positive polarity output terminal of M2 links to each other with contact A, and the negative polarity output is through current source Q, resistance R 5 back ground connection; Go up inclined to one side resistance R 7 one ends and link to each other with the A point, the other end is connected in the base stage of Q; Feedback resistance R4 is with after high-frequency filter capacitor C3 connects, and cross-over connection is in R7 and ground end, and C3 is used for the high-frequency noise that filtering circuit is difficult to offset fully or circuit self produces.

Above-mentioned a kind of microphone circuit with high noise resistance, it is characterized in that described M1, M2 the opposite signal of two phase places from noise source in the output of A point, parameter by the regulating circuit element, make the two amplitude equal and opposite in direction, guarantee the A point and " " between output signal be zero (being that noise is suppressed to zero), and sound signal from A point and " " between export.

Description of drawings:

Fig. 1 is the circuit theory diagrams of electret microphone

Fig. 2 is circuit theory diagrams of the present invention

The invention will be further described below in conjunction with accompanying drawing 1,2:

That the present invention adopts is two Electret condenser microphone M1, M2, in order to make two Electret condenser microphones under same noise circumstance, pick up identical noise signal, but reduce under same environment, to pick up identical voice signal, so as far as possible, two microphones towards should be opposite, and at a distance of certain distance.

M2 of the present invention is equivalent to former audio microphone, its anode still is connected to former microphone positive polarity input, but negative pole is to connect to former microphone negative polarity input through current source Q, when M2 senses acoustic signals, its internal resistance changes, A point current potential is changed with the size variation of the sound intensity, and the rule of variation is identical with the sound wave Changing Pattern; Its internal resistance also changes with B point potential change, and this variable quantity is coupled to the base stage of Q through C2, R3, concerning B point signal, Q is the common emitter current amplifier, B point signal is here by anti-phase amplification, and the Q that promptly flows through also is the electric current that flows through M2, and is opposite with the M1 phase of output signal.

When if M1, M2 sense the identical acoustic signals of equal and opposite in direction, phase place simultaneously, (as ambient noise signal), M1, M2 can produce the identical signal output of phase place so, because Q is anti-phase with the output signal of M1, thereby the A output signal of ordering becomes the M1 output signal and deducts the M2 output signal, when the regulating circuit component parameters made the two amplitude equal and opposite in direction, A point output signal was zero (being that noise is suppressed to zero).

When importing as audio frequency, sound signal (as voice signal) direction is pointed to M2, with the M1 of M2 rightabout device, experiences strong, two voice signals a little less than, and promptly the sound signal of M1 is much smaller than M2; Two noise signals that waveform is identical, phase place is opposite, just cancel out each other at the A point, just the M1 output signal far can not be offset the output signal of M2 fully, behind the A point, some that strong voice signal is weakened, but for whole voice signal is inappreciable, so, sound signal is from the output of A point, because there is voice acoustic pressure by a relatively large margin in two microphones of adding, therefore, voice signal is able to by the sound wave output line, through the compression amplification filtering of voice preamplifier, so, the present invention will export voice signal clearly again.C3 is used for the high-frequency noise that filtering circuit is difficult to offset fully or circuit self produces.

Claims

1, a kind of microphone circuit with high noise resistance is characterized in that: adopt two electret microphone M1, M2; Utilize the circuit in-line power; The positive polarity output terminal of M1 is connected in the contact B between load resistance R2 and the output coupling capacitance C2, the negative polarity output head grounding, C2 and the base stage that is connected to current source Q after current-limiting resistance R3 connects, the potential change amount that C2, R3 are ordered B is coupled to the base stage of Q, for the B point, Q is the common emitter current amplifier, with the anti-phase amplification of its output signal; Audio output coupling capacitance C4, isolation resistance R1 connect with filter capacitor C1, another termination audio frequency output of C4, C1 other end ground connection; The positive polarity output terminal of M2 links to each other with contact A, and the negative polarity output is through current source Q, resistance R 5 back ground connection; Go up inclined to one side resistance R 7 one ends and link to each other with the A point, the other end is connected in the base stage of Q; Feedback resistance R4 is with after high-frequency filter capacitor C3 connects, and cross-over connection is in R7 and ground end, and C3 is used for the high-frequency noise that filtering circuit is difficult to offset fully or circuit self produces.

2, a kind of microphone circuit with high noise resistance as claimed in claim 1, it is characterized in that described M1, M2 the opposite signal of two phase places from noise source in the output of A point, parameter by the regulating circuit element, make the two amplitude equal and opposite in direction, guarantee the A point and " " between output signal be zero (being that noise is suppressed to zero), and sound signal from A point and " " between export.

3, a kind of microphone circuit with high noise resistance as claimed in claim 1 is characterized in that described M1, M2's is opposite towards arranging.