Coded data generation or conversion – Analog to or from digital conversion – Increasing converter resolution
Patent
1991-05-21
1992-09-01
Williams, Howard L.
Coded data generation or conversion
Analog to or from digital conversion
Increasing converter resolution
341143, H03M 120
Patent
active
051443082
ABSTRACT:
Technique for adding a dither signal to a sigma-delta modulator to remove low level tones and periodic noise in the desired passband of the modulator when no, or a very low, signal is present (idle). The dither signal is a high-level signal added to the imput of an quantizer in the modulator, the normalized power in the AC component thereof being at least about ##EQU1## of the square of the quantizer step, where N is the order of the modulator. No significant reduction in the dynamic range of the modulator results. The technique may also be applied to multiple order sigma-delta modulators as well as to multiple stage sigma-delta modulators. Further, the dither may be added at any point in the modulator with suitable filtering of the dither. The transfer function of the filter is proportional to the noise shaping transfer function of the modulator between the point of addition of the dither and the input to the quantizer.
REFERENCES:
patent: 3999129 (1976-12-01), Kasson
patent: 4761634 (1988-08-01), Yamaguchi et al.
patent: 5010347 (1991-04-01), Yukawa
patent: 5055843 (1991-10-01), Ferguson, Jr. et al.
patent: 5073777 (1991-12-01), Fukuhara et al.
"A Voiceband Codec with Digital Filtering", IEEE Transactions on Communications, vol. COM-29, No. 6, Jun. 1981 James C. Candy, Bruce A. Wooley, Oconnel J. Benjamin pp. 815 through 830.
"Use of Double Integration is Sigma Delta Modulation", IEEE Transactions on Communications, vol. COM-33, No. 3, Mar. 1985 James C. Candy pp. 249 through 258.
"Maximum-Length Shift-Register Codes", Digital Communications, pp. 256 through 258, John G. Proakis, McGraw-Hill Book Company, Copyright 1983.
AT&T Bell Laboratories
McLellan S. W.
Williams Howard L.
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