Side tone preventive circuit for telephone

Details Side tone preventive circuit for telephone Side tone preventive circuit for telephone

1989-11-27

1991-07-02

Ng, Jin F.

Telephonic communications

Substation or terminal circuitry

Sidetone control or hybrid circuit

379392, H04M 158

Patent

active

050292030

ABSTRACT:
A side tone preventive circuit for telephones which prevents the output of the transmitter on the speaker's side from being transmitted to the receiver on the same side. The balance of the impedance bridge in a bridge circuit for separating a transmission signal and a reception signal is automatically adjusted in accordance with the circuit impedance at the location at which a telephone is installed. An impedance measuring circuit measures the impedance of the telephone circuit, and a balance adjustment circuit the impedance of which is adjustable is provided in the bridge circuit. The impedance of the telephone circuit is measured at the time of installation of a telephone, and the impedance of the balance adjustment circuit is adjusted in correspondence with the result of measurement. Thus, the impedance balance of the bridge circuit is adjusted in correspondence with the circuit impedance, thereby effectively preventing a side tone.

REFERENCES:
patent: 3441684 (1969-04-01), McLeod
patent: 3462560 (1969-08-01), Holzman
patent: 3647982 (1972-03-01), van der Puije
patent: 4081620 (1978-03-01), Goodman et al.
patent: 4283675 (1981-08-01), Sparber
patent: 4354060 (1982-10-01), Niertit et al.
patent: 4715064 (1987-12-01), Claessen

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