Bell Telephone Laboratories

American Telephone & Telegraph Co., At&t Bell Laboratories

Joseph F Carriere

Joseph Elide Landry

Dewayne Alan Spires

Philip J Baun, Jr

Stephen K Eng

Wilmer B Gaunt, Jr

Jonghee Lee

Thomas M Nolan

David C Rhodes

A channel bank unit for interfacing baseband user signals with a PCM carrier communications channel. The channel bank unit includes a circuit allowing verification of the transmission interity between the channel bank unit and external equipment having two-way communication with the channel bank unit. The circuit includes a first portion for evaluating the reception integrity of signals received from the external equipment and a second portion for imposing a parity sense on the signals transmitted to the external equipment that is related to the evaluation results of the first portion.

D-5 Channel bank control structure and controller

A reduction in idle channel noise and crosstalk in a mid-riser-biased successive approximation encoder is achieved through the use of two polarity decisions. Encoder (401) assigns a sampled analog input signal to the closest one of a multitude of discrete signal levels or code steps. A comparator (109) provides this assignment by successive comparisons of the sampled signal with a series of reference signals (110). Each comparison produces a binary digit. The first comparison, or polarity decision, is not transmitted and instead coupled to feedback circuitry (401) to reduce any dc component in the analog input signal to substantially zero. A second polarity decision is then made using a non-zero offset reference signal (402) corresponding to an intermediate position on a code step, typically the midpoint. The non-zero offset reference signal is applied along with subsequent reference signals to the comparator to determine the closest code step. The binary digit from the second polarity decision, along with the binary digits representing the code step, are coupled to the encoder output. Accordingly, the encoder is now biased at the intermediate position to substantially reduce the likelihood of idle channel noise and crosstalk enhancement.

Noise and crosstalk reduction in mid-riser biased encoders

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Andover, MA, United States of America

Joseph F Carriere