Invalidity dossier
US 4965822
Full duplex speakerphone
Current assignee: Asure Software Inc
Added 9/23/2026, 4:55:28 PM
Active provider: DeepSeek · deepseek-flash
Patent summary
Title, assignee, inventors, filing/issue dates, abstract, and a plain-language overview of the claims.
US4965822A — Full Duplex Speakerphone: Overview
Title: Full duplex speakerphone
Patent number: US4965822A
Application number: US07/335,239
Inventor: Errol R. Williams
Original assignee: VideoTelecom Corp (later recorded as VTEL Corporation; current assignee listed as Asure Software Inc)
Priority/filing date: 1989-04-10
Publication (grant) date: 1990-10-23
Legal status (as listed): Expired – Fee Related; anticipated expiration 2009-04-10
Classification: H04M9/08, H04M9/082 — two-way loud-speaking telephone systems with echo cancellers
Purpose. The patent relates generally to telecommunications and specifically to methods and apparatus for echo and feedback suppression in full-duplex speakerphone voice communication. The stated objects are: improved echo suppression during intervals of voice communication; avoiding excessive signal-level increases during periods of silence when neither party speaks; and echo suppression at low signal levels that is not apparent to the communicating parties.
Plain-language scope. The described speakerphone is an adaptive FIR (Finite Impulse Response) filter speakerphone. Digitized received and transmitted signals are processed by digital circuits providing adaptive FIR filters and summing junctions, with ADCs and DACs converting between analogue and digital domains, plus variable-gain amplifiers for the received and transmitted signals. Two adaptive FIR filters cancel echo in both directions between the received-signal and transmitted-signal summing junctions. The improvement described is a tracking comb filter interposed between the output of the transmitted-signal summing junction and the telephone line, applied when the characteristics of the received signal meet conditions stated in the description. The text discusses problems with prior voice-switching (simplex) speakerphones, residual echo, and AGC raising gain during silence so that background room noise dominates.
Not established by this excerpt. The excerpt omits the claims, abstract, and much of the description, so the exact claimed scope, claim count, and claim language are not established here. It also does not provide the comb filter's detailed structure, control logic, or the specific received-signal characteristics triggering its use. Numerical ranges, embodiments, and any drawing content are not available in the excerpt. No statements are made here regarding validity, litigation, or prior art beyond the background discussion quoted.
Source: https://patents.google.com/patent/[US4965822](/patent/US4965822)/en
Generated 10/1/2026, 9:44:01 PM
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Litigation summary
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PTAB challenges
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Assignment history
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Prior art
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Derivative works
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