Telephonic communications – Substation or terminal circuitry – Conversion of signal form
Patent
1996-08-07
1998-11-03
Matar, Ahmad F.
Telephonic communications
Substation or terminal circuitry
Conversion of signal form
379377, 379395, 381112, H04M 160
Patent
active
058320768
ABSTRACT:
An apparatus and method for determining the presence and polarity of DC bias voltage at a telephone microphone. A circuit can be added in parallel between any hand or headset and a telephone base unit. The circuit converts the DC bias voltage, if any, across the microphone into a pulsed signal. Each pulse charges a capacitor. The output of the capacitor is passed through a resistor transformer network, and sampled. In between each pulse, the capacitor is discharged and the resulting signal is passed through the transistor/resistor network and sampled. By determining the averages of the charging and discharging signals, and sampling them to convert it into digital information, a digital signal processor can derive whether any bias voltage is present across the microphone, and, if so, its polarity. The circuit can be electrically isolated from the microphone and telephone.
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Dilley David L.
Holthaus James R.
Matar Ahmad F.
Saint-Surin Jacques M.
Transcrypt International, Inc.
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