# US 5,706,354 A · AC line-correlated noise-canceling circuit > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 5,706,354 A - Document ID: US5706354A - Status: Granted - Kind: A - Application number: 08/500,259 - Filed: 1995-07-10 - Granted: 1998-01-06 - Earliest claimed: 1995-07-10 - Inventors: Brian A. Stroehlein - Web page: https://patentgrep.com/patent/US5706354A ## CPC - H04B 15/00: Suppression or limitation of noise or interference (by means associated with receiver H04B1/10) - H04B 1/123: {using adaptive balancing or compensation means (adaptive filter circuits and algorithms H03H)} - H04B: TRANSMISSION ## 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. ## Claims ### Claim 1 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. ### Claim 2 (depends on 1) The system of claim 1 wherein said noise signal comprises power line interference. ### Claim 3 (depends on 1) The system of claim 1 wherein said storage means are digital storage means. ### Claim 4 (depends on 1) The system of claim 1 wherein said storage means are analog storage means. ### Claim 5 (depends on 1) The system of claim 1 wherein said gain/attenuation adjustment means are automatically adjusted by said control logic circuit. ### Claim 6 (depends on 2) The system of claim 2 wherein said gain/attenuation adjustment means are automatically adjusted by said control logic circuit. ### Claim 7 (depends on 3) The system of claim 3 wherein said gain/attenuation adjustment means are automatically adjusted by said control logic circuit. ### Claim 8 (depends on 4) The system of claim 4 wherein said gain/attenuation adjustment means are automatically adjusted by said control logic circuit. ### Claim 9 A method for canceling an unwanted noise signal having a relatively fixed frequency and phase, while preserving the frequency, phase and transient characteristics of a desired signal containing the same frequency, said method comprising: a) simultaneously adjusting the gain/attenuation at the input and output of a waveform acquisition/playback means using an electrically or mechanically ganged gain/attenuation adjustment means, when only said noise signal is present and with aid of a threshold detector means; b) sampling said noise signal at N preset intervals when only said noise signal is present, whereby the greatest use and economy of limited dynamic range of said waveform acquisition/playback means is realized during sampling by virtue of step (a); c) separately storing the values obtained during said sampling; d) discontinuing said sampling; and e) retrieving the stored signals and combining the retrieved signals with the desired signal to cancel the unwanted noise. ### Claim 10 (depends on 9) The method of claim 9 in which said sampling is phase-correlated to the noise signal. ### Claim 11 The use of a method for non-adaptively canceling in an audio signal an unwanted noise signa having a relatively fixed frequency and phase, while preserving the frequency, phase and transient characteristics of a desired signal containing the same frequency, said method comprising: a) simultaneously adjusting the gain/attenuation using electrical or mechanical ganged volume controls with complimentary gain/attenuation characteristics at the input and output of a waveform acquisition/playback means, whereby the greatest use and economy of limited dynamic range of said block is realized, said adjusting occurring when only said noise signal is present and with aid of a threshold detector means; b) sampling said noise signal at N preset intervals when only said noise signal is present, whereby the greatest use and economy of limited dynamic range of said waveform acquisition/playback means is realized during sampling by virtue of step (a); c) separately storing the values obtained during said sampling; d) discontinuing said sampling; and e) retrieving the stored signals and combining the retrieved signals with the desired signal to cancel the unwanted noise.