I've been trying for a little over two weeks now to get an understanding of how an Electret microphone works. I've scoured web forums, manufacturer data sheets and have run several simulations inside of Multisim and still don't have a solid idea of how they work.
I have the following questions...
1.) What kind of signal does an Eletrect microphone produce? Specifically, is it AC centered at 0 (e.x. high peak at +1 V and low peak at -1 V ), or AC centered at somewhere else (with low peak at 0 and high peak somewhere +V).
My current understanding is as follows. The microphone contains a N-channel JFET with its gate connected to the sound sensing element. Since its an N-channel type when the sound sensor "capicitor" is compressed it produces a negative bias on the gate this reducing current from source to drain. My reasoning says that if the microphone is not hearing any sound, the output would be a steady +V DC signal determined by the "biasing" resistor and the internal JFETs Ids spec. (See http://en.wikipedia.org/wiki/File:Electret_condenser_microphone_schematic.png ). When the microphone does hear sound, that DC signal is reduced in relation to the incomming sound pressure, thus producing and AC signal ranging from its "off" +V DC voltage down to a minimum of 0 volts. Am I correct or just dumb as a box of rocks?
2.) Along the same lines, I've seen circuit drawings that have no apparent source of -V yet are connected to standard speakers. See http://www.elecfree.com/electronic/warbling-alarm-circuit-with-tone-generator/. Are these circuits driving the speakers with an AC signal that never goes below 0 volts? I don't see how that could work since the current is always moving in the same direction, or not at all (at 0 volts). The speaker cone should move out for any changeing +V signal but there would be nothing to pull it back in other than the natural elasticity of the speaker suround.
That leaves 1 final question.
3.) I've seen some proper audio amplifier circuit drawings that show an OPAMP that has +V, -V, and 0V connections. This makes sense to me as the +V input would be used to source the amplification on the incoming +V audio sine wave and the -V would amp the - side of the audio sine wave. My question is how do you get a -V reference from a battery power circuit? Say one that contains only 1 9volt battery?
Thanks a ton in advance for all those who are helping my sanity
Scott
I have the following questions...
1.) What kind of signal does an Eletrect microphone produce? Specifically, is it AC centered at 0 (e.x. high peak at +1 V and low peak at -1 V ), or AC centered at somewhere else (with low peak at 0 and high peak somewhere +V).
My current understanding is as follows. The microphone contains a N-channel JFET with its gate connected to the sound sensing element. Since its an N-channel type when the sound sensor "capicitor" is compressed it produces a negative bias on the gate this reducing current from source to drain. My reasoning says that if the microphone is not hearing any sound, the output would be a steady +V DC signal determined by the "biasing" resistor and the internal JFETs Ids spec. (See http://en.wikipedia.org/wiki/File:Electret_condenser_microphone_schematic.png ). When the microphone does hear sound, that DC signal is reduced in relation to the incomming sound pressure, thus producing and AC signal ranging from its "off" +V DC voltage down to a minimum of 0 volts. Am I correct or just dumb as a box of rocks?
2.) Along the same lines, I've seen circuit drawings that have no apparent source of -V yet are connected to standard speakers. See http://www.elecfree.com/electronic/warbling-alarm-circuit-with-tone-generator/. Are these circuits driving the speakers with an AC signal that never goes below 0 volts? I don't see how that could work since the current is always moving in the same direction, or not at all (at 0 volts). The speaker cone should move out for any changeing +V signal but there would be nothing to pull it back in other than the natural elasticity of the speaker suround.
That leaves 1 final question.
3.) I've seen some proper audio amplifier circuit drawings that show an OPAMP that has +V, -V, and 0V connections. This makes sense to me as the +V input would be used to source the amplification on the incoming +V audio sine wave and the -V would amp the - side of the audio sine wave. My question is how do you get a -V reference from a battery power circuit? Say one that contains only 1 9volt battery?
Thanks a ton in advance for all those who are helping my sanity
Scott