US 5,706,354 A · AC line-correlated noise-canceling circuit

Abstract

A device is connected in a signal path for canceling an unwanted noise signal induced by and correlated to the AC power line. The noise signal is assumed to have relatively constant phase (with respect to the AC power line) and amplitude during the period of use. The desired signal is assumed to be temporarily mutable for a brief period during which the noise signal is acquired. A manually- or automatically-adjusted gain (or attenuation) stage and overload detector are at the front-end of the waveform acquisition/playback block. A manually- or automatically-adjusted stage, typically linked to the earlier gain (attenuation) stage and with complementary attenuation (or gain) is at the back-end of the waveform acquisition/playback block. In this way, maximum performance can easily be realized from a waveform acquisition/playback block of lower resolution over a wide range of noise signal levels. The device acquires N samples of the noise signal over one or more periods of the AC power cycle and in synchrony with the AC power cycle. The sampling is terminated and the stored signals are played back with the correct amplitude and summed 180 degrees out-of-phase with the original noise signal.

Claims11

Dependent claims

A system for canceling an unwanted noise signal while preserving a desired signal having the same frequency, said system comprising:

a) a waveform acquisition/playback block with integral interconnected sample recording, N-unit storage, and sample playback means, integral threshold detector means connected at sampling circuit input within said block, and electrically or mechanically ganged gain/attenuation adjustment means with complimentary gain/attenuation characteristics connected at input and output of said block for simultaneously adjusting the input and output of said block to a correct amplitude whereby the greatest use and economy of limited dynamic range of said block is realized;
b) an address means, said address means having N positions and being operable in synchronism with said noise signal;
c) a control logic circuit coupled to said waveform acquisition/playback block and address means to enable said block at selected times to store the instantaneous values of said noise signal, enable said block at other times to play back the stored instantaneous values of said noise signal, and to manually or automatically simultaneously scale the input and output of said block using said gain/attenuation adjustment means to the correct amplitude with reference to said threshold detector means prior to acquisition of said noise signal;
d) a feedforward circuit whereby said acquired noise signal is summed inverted with respect to said unwanted noise signal superimposed on said desired signal during operation.

1 more element

Dependencies are inferred from the claim text.

AC line-correlated noise-canceling circuit

Life of this patent

AC line-correlated noise-canceling circuit

Life of this patent

Abstract

Claims11