Electret condensor microphone preamplifier that is insensitive to leakage currents at the input
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United States of America Patent
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Sep 19, 2006
Grant Date -
Sep 12, 2002
app pub date -
Mar 8, 2002
filing date -
Mar 9, 2001
priority date (Note) -
Expired
status (Latency Note)
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Abstract
A preamplifier having extremely high input impedance amplifies the electrical signal output from an electret condenser microphone (ECM) without suffering from the effects of a DC leakage current at the input. The preamplifier circuit includes a pair of cross-coupled PN junction diodes setting the input impedance, a PMOS device, and a load resistor configured similarly to a conventional preamplifier. A capacitor is placed between the input and the cross-coupled diodes such that a DC path no longer exists to bias the cross-coupled diodes. Therefore, leakage currents are prevented from upsetting the DC operating point of the preamplifier and biasing the cross-coupled diodes. Consequently, small signal gain distortion, excessive demodulation products and increased noise can be avoided.
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