At&t Bell Laboratories

Bell Telephone Laboratories

Steve W Bell

Milton L Embree

Michael Sabin

Robert L Breeden

There is disclosed a precision linear comparator for a speakerphone circuit having two rectifying constant voltage nodes for separately summing two groups of signals derived from a speakerphone transmit channel and receive channel and supplying at an output terminal a signal representative of the difference between two unblocked summed signals. Each node blocks its summed signal if the signal is not representative of a true voice signal. A null signal is supplied at the output terminal during the absence of unblocked summed signals.

Speakerphone linear comparator

In certain situations it is necessary to detect a slight change in a continuous wave signal and to be able to specifically determine the exact position of the change. This is especially necessary in situations where a continuously changing signal (with respect to time) is generated and where it is necessary to determine, at a particular instant of time, any change in the signal from a previous corresponding instant of time. Where the signal is periodic in nature and substantially repeatable between cycles it is possible to establish a memory data base of signal levels as a function of time. Comparisons can then be made on successive cycle against the known, or precalculated data base. Changes between the data base and the new signal result give a positive signal change indication.

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Steve W Bell