Electronic telephone relay
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United States of America Patent
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-
Nov 26, 1985
Grant Date -
N/A
app pub date -
Feb 16, 1983
filing date -
Feb 16, 1983
priority date (Note) -
Expired
status (Latency Note)
Importance
Abstract
An electronic relay circuit for replacement of an A-type relay in a step-by-step selector and connector of a telephone exchange system is implemented with a first operational amplifier (10) connected to the tip (T) and ring (R) conductors of a telephone line, and a second operational amplifier (24') with hysteresis for use as a comparator. A capacitor (C1) with a diode (D1) in parallel couples the input terminal of the comparator to a reference voltage from a voltage divider (R1, R2) in order that signal transitions from the input amplifier appear as common mode signals for a period determined by the RC time constant of a coupling resistor (R3) for ON-HOOK to OFF-HOOK transitions limited in amplitude by the parallel diode (D1) and the RC time constant of a resistor (R4) connected to a source of negative voltage for OFF-HOOK to ON-HOOK transitions limited in amplitude by a series diode (D2). A diode (D3) in series with the voltage divider introduces a compensating voltage drop for the diode (D2). The first amplifier is provided with a low-pass band of at least twice the dialing frequency (15 Hz).
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