Electret microphone transmitter for use in telephone circuits

Details Electret microphone transmitter for use in telephone circuits Electret microphone transmitter for use in telephone circuits

1990-02-20

1991-07-30

Dwyer, James L.

Telephonic communications

Substation or terminal circuitry

Conversion of signal form

379395, 381111, H04M 160

Patent

active

050365363

ABSTRACT:
A transistor 12 is provided for interfacing an electret microphone 16 to a carbon compatible telephone network by impedance matching. The transmitter 12 includes a rectifier 14 constructed from a plurality of Schottky diodes 44, 46, 48, 50 to reduce voltage drop therein and to provide a stable DC voltage supply to the transmitter 12. An amplifier 18 receives an audio signal from the electret microphone 16, amplifies it, and delivers this amplified signal onto the carbon compatible network via the rectifier 14. The amplifier 18 accomplishes this impedance matching while minimizing voltage drop therein. The amplifier 18 includes a first bipolar transistor 68 having its base connected to the microphone 16 and its emitter connected to the negative terminal of the rectifier 14. A second bipolar transistor 70 is connected as an emitter follower.

REFERENCES:
patent: 3867576 (1975-02-01), Simonsen
patent: 4233474 (1980-11-01), Hishinyma et al.
patent: 4378467 (1983-03-01), Ferrantelli
patent: 4461929 (1984-07-01), Britt
patent: 4491697 (1985-07-01), Tanaka et al.
patent: 4629910 (1986-12-01), Early et al.
patent: 4649565 (1987-03-01), Kaizer et al.
patent: 4757545 (1988-07-01), Rosander

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