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:
Aug. 21, 1984
Filed:
Dec. 16, 1981
Jean Lassaux, Orvault, FR;
Abstract
A digital echo canceller is arranged in a digital telephone circuit for PCM-signals in accordance with a pseudo-logarithmic encoding law, for example the A-law of the CCITT, in the proximity of a subscriber line interface circuit having a codec in order to cancel in the near-end speech signals S supplied by the codec to the send path the echo effect Y of the far-end speech signals X conveyed to the codec by the receive path. The echo canceller has circulating shift registers for the signals X and the coefficients C, digital correlation calculation means for obtaining the coefficients C, digital convolution calculation means for obtaining an echo cancellation signal y and digital subtraction calculation means for obtaining near-end speech signals R in which the echo effect Y has been substantially cancelled. Each of the digital correlation, convolution and subtraction calculation means incorporates only one pseudo-logarithmic-to-linear code converter, and furthermore the digital subtraction calculation means incorporates only one linear-to-pseudo-logarithmic code converter.