Full duplex modems and synchronizing methods and apparatus there

Details Full duplex modems and synchronizing methods and apparatus there Full duplex modems and synchronizing methods and apparatus there

1981-11-19

1984-06-19

Griffin, Robert L.

Pulse or digital communications

Repeaters

Testing

375103, 179 16A, H04B 110

Patent

active

044556632

ABSTRACT:
Full duplex modems and synchronizing methods and apparatus therefor which allow the relatively low cost realization of full duplex modems compatible with prior art data sets such as the Bell System 212A Data Set. The modems utilize relatively little bandpass line filtering with post demodulation filters which provide normal filtering of second harmonic products, but further also serving to make up for the lack of the ordinarily heavy line or predemodulation filtering commonly used to reject the other channel. In addition, the automatic gain control is provided after the post demodulation filters rather than on the incoming line itself. Carrier sync and timing error corrections are provided under software control, with timing error corrections being achieved by sensing certain phase differences and providing a correction in response thereto. The use of switched capacitor filters, as well as other techniques herein disclosed, allows the use of two identical large scale integrated circuits to provide most of the transmit and receive functions of the modem.

REFERENCES:
patent: 3646448 (1972-02-01), Harmon, Jr. et al.
patent: 3669511 (1972-09-01), Motley et al.
patent: 4004226 (1977-01-01), Qureshi et al.
patent: 4137427 (1979-01-01), Choquet et al.
patent: 4227252 (1980-10-01), Godard
patent: 4295222 (1981-10-01), Van Uffelen
patent: 4312075 (1982-01-01), Murano et al.
patent: 4344176 (1982-08-01), Qureshi
patent: 4352194 (1982-09-01), Caracappa

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