Digital telephone system noise reduction circuit

Details Digital telephone system noise reduction circuit Digital telephone system noise reduction circuit

1992-04-02

1994-01-11

Dwyer, James L.

Telephonic communications

Subscriber line or transmission line interface

379201, H04M 100, H04M 342

Patent

active

052788997

ABSTRACT:
A telephone system uses above voice-band ASK control and supervisory signals which are appended to digitally encoded voice by forcing the least significant bits to a selected level for transmission to the receiving end. At the receiving end, the ASK is regenerated by a circuit including special filter and a pulse generator. To eliminate audible noise resulting from the filter action, the ASK signal or the pulses from the pulse generator is shifted in phase by about 90.degree. before application to a filter. The result is significantly reduced noise.

REFERENCES:
patent: 4901344 (1990-02-01), Monette et al.
patent: 4987573 (1991-01-01), Monette et al.
patent: 5016246 (1991-05-01), Wisniewski
patent: 5142402 (1992-08-01), Tsushima et al.

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