Electrical audio signal processing systems and devices – Circuitry combined with specific type microphone or loudspeaker – With electrostatic microphone
Reexamination Certificate
2006-09-19
2006-09-19
Grier, Laura A. (Department: 2644)
Electrical audio signal processing systems and devices
Circuitry combined with specific type microphone or loudspeaker
With electrostatic microphone
C381S111000, C381S120000
Reexamination Certificate
active
07110560
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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International Search Report, PCT/DK 02/00147, Sep. 13, 2000.
Grier Laura A.
Harness Dickey & Pierce
Sonion A/S
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