The single FET in an electret microphone's housing may soon become an endangered species. National Semicon-ductor Corp. of Santa Clara, Calif., has two amplifiers that replace the junction FET (JFET) in current electret mikes.
A high-gain amplifier for two-wire ECMs, the LMV1012 features a built-in gain of 17 dBV optimized for handset microphones. New ECMs using the LMV1012 offer total harmonic distortion of 0.1%, signal-to-noise ratio (SNR) greater than 55 dB, and supply current less than 240 µA. The LMV1014 is an amplifier for three-wire, low-current, and low-noise ECMs. It draws less than 40 µA while providing a low output impedance of 200 Ω. Its power-supply rejection ratio (PSRR) tops 60 dB, and its SNR exceeds 55 db.
The LMV1012 and 1014 come in four-bump micro-SMD packaging. They cost $0.39 and $0.49, respectively, in 1000-unit quantities.
National Semiconductor Corp.