The patent badge is an abbreviated version of the USPTO patent document. The patent badge does contain a link to the full patent document.
The patent badge is an abbreviated version of the USPTO patent document. The patent badge covers the following: Patent number, Date patent was issued, Date patent was filed, Title of the patent, Applicant, Inventor, Assignee, Attorney firm, Primary examiner, Assistant examiner, CPCs, and Abstract. The patent badge does contain a link to the full patent document (in Adobe Acrobat format, aka pdf). To download or print any patent click here.
Patent No.:
Date of Patent:
Jul. 05, 1977
Filed:
Jun. 30, 1976
Victor Bernard Lawrence, Matawan, NJ (US);
Kent Vincent Mina, Colts Neck, NJ (US);
Bell Telephone Laboratories, Incorporated, Murray Hill, NJ (US);
Abstract
In U.S. Pat. No. 3,906,199, issued to R. B. Kieburtz and K. V. Mina on Sept. 16, 1975, limit cycle noise is reduced in a second order recursive digital filter by a circuit which randomly inhibits the rounding signal in one of the digital multipliers disposed in the filter. It has been found, however, that in certain instances, this approach results in even longer transients. In accordance with the present invention, random inhibiting is constrained to instances in which limit cycle noise is reduced, by monitoring, with suitable logic circuitry, the signals present in the various feedback loops of the filter. Generally, it has been found that the inhibiting circuit should be allowed to operate only if D.sub.1 and D.sub.2 satisfy predetermined magnitude and polarity relationships, where D.sub.1 .ident. a version of the filter output signal Y(n) that is removed in time by one sample interval, and D.sub.2 .ident. a version of the filter output signal Y(n) that is removed in time by two sample intervals. In accordance with another aspect of the invention, DC and half sampling rate limit cycles are eliminated by monitoring three consecutive values of D.sub.1 or, alternatively, the present values of Y(n), D.sub.1 and D.sub.2. If the same magnitudes are detected, the magnitude of the next D.sub.1 is reduced by one.