Digital filter for a modem sigma-delta analog-to-digital convert

Details Digital filter for a modem sigma-delta analog-to-digital convert Digital filter for a modem sigma-delta analog-to-digital convert

1989-08-21

1990-11-20

Shaw, Dale M.

Boots, shoes, and leggings

36472410, 341143, G06F 1531, H03M 300

Patent

active

049723600

ABSTRACT:
Digital filter used in a sigma-delta decoder wherein each input sample is involved in the computation of three consecutive pulse coded modulation (PCM) output samples. During one sigma-delta sampling period, the filter performs three parallel operations by multiplexing one adder running three times faster than the sigma-delta clock for loading one of three accumulators. As the analog-to-digital converter must be kept in phase with remote modem transmit clock, the PCM sampling clock is controlled by the phase tracking performed by adding or subtracting one period of the crystal oscillator from time to time to the PCM sampling clock period. Rotating the order in which the accumulators are loaded by the adder each PCM sampling time enables having zero as the last coefficient value to add to the accumulator, the contents of which is used as PCM output samples. Thus, each PCM sample value is available in the corresponding accumulator one sigma-delta clock period before the last computation. In case of a correction which shortens or lengthens the PCM sampling period, this correction does not change the PCM sample value to be output since the last computation which is either cancelled or repeated, consists in adding zero to the previous accumulator contents.

REFERENCES:
patent: 3959637 (1976-05-01), Nussbaumer
patent: 3968354 (1976-07-01), Ferrieu
patent: 4796004 (1989-01-01), Rich et al.
Proceedings IEEE International Conference on Acoustics, Speech and Signal Processing, 26th-29th Mar. 1985, Tampa, Florida, vol. 3, pp. 1380-1383.
Proceedings IEEE-IECEJ-ASJ International Conference on Acoustics, Speech and Signal Processing, 7th-11th Apr. 1986, Tokyo, vol. 4, pp. 2595-2598.
1987 IEEE International Symposium on Circuits and Systems, 4th-7th May 1987, Philadelphia, PA, vol. 2, pp. 479-482.
G. Jones, Jr., Programmable Transversal Filter, IBM Technical Disclosure, Bulletin, vol. 13, No. 8, Jan. 1971, pp. 2463-2464.

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