Telephone subscriber line unit with sigma-delta digital to analo

Details Telephone subscriber line unit with sigma-delta digital to analo Telephone subscriber line unit with sigma-delta digital to analo

1979-11-28

1981-05-26

Atkinson, Charles E.

179 1555R, 179 2DP, H04M 100

Patent

active

042700272

ABSTRACT:
A digital to analog converter is employed in the digital line circuit of a telephone system and operates to convert a digital signal indicative of an analog speech signal back into a replica of the analog signal. The converter operates with an interpolated input digital signal to detect by means of a sign bit, the characteristic of an input digital word as being indicative of a positive or negative level. An error correcting signal is provided by the converter which is added to the next digital word to provide a compensated word having a sign bit determined by the remainder and the sign bit of the previous digital word. This word is then processed in sequence to produce an output pulse stream from the sign detector indicative of successive positive or negative values as defined by the input digital words, each of which are modified according to the error correcting signal.

REFERENCES:
patent: 3542956 (1970-11-01), Sekimoto
patent: 3924077 (1975-12-01), Blakeslee
patent: 3973081 (1976-08-01), Hutchins
patent: 4020332 (1977-04-01), Crochiere et al.
patent: 4100373 (1978-07-01), Perkins
patent: 4109110 (1978-08-01), Gingell
patent: 4124773 (1978-11-01), Elkins
patent: 4150260 (1979-04-01), Kamata
P. Van Gerwen, et al., "A New Type of Digital Filter etc.", IEEE Trans. on Comm., Feb. 1975, pp. 222-234.
M. Tubiana, "Digital Filter Having Integral Coefficients", IBM Tech. Discl. Bull., Mar. 1976, pp. 3322-3324.

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