Sigma-delta modulator having a plural order loop filter with suc

Details Sigma-delta modulator having a plural order loop filter with suc Sigma-delta modulator having a plural order loop filter with suc

1992-02-21

1993-09-07

Williams, Howard L.

Coded data generation or conversion

Analog to or from digital conversion

Differential encoder and/or decoder

H03M 300

Patent

active

052433455

ABSTRACT:
A sigma-delta modulator comprising a low-pass filter of the Nth order, which is constituted by a series combination of N first-order integrating sections (6.1, 6.2, 6.3, . . . , 6.N) each comprising an integrator (12.1, 12.2, 12.3, . . . , 12. N) and a limiter (14.1, 14.2, 14.3, . . . , 14.N). The individual output signals of the sections are weighted by means of corresponding weighting amplifiers (16.1, 16.2, 16.3, . . . , 16.N) and the weighted signals are added together by an adder stage (18). The gains of the sections and the limit values of the limiters are selected so that the last limiter (14.N) in the series arrangement is activated first as the input signal level to the sigma-delta modulator increases, then the last-but-one limiter, and so on. This reduces the order of the filter system each time by one section as the input signal level increases above each successive limit value, thereby causing the sigma-delta modulator to remain stable at all signal levels.

REFERENCES:
patent: 4509037 (1985-04-01), Harris
patent: 4772871 (1988-09-01), Suzuki et al.
patent: 5012244 (1991-04-01), Wellard et al.
patent: 5055846 (1991-10-01), Welland
Chao et al., "A Higher Order Topology for Interpolative Modulators for Oversampling A/D Converters", IEEE Trans. Circuit and Sys. vol. CAS-37, Mar. 1990 pp. 309-318.
Candy et al. "Oversampling Methods for A/D and D/A Conversion", 1992, from IEEE Oversampling Delta-Sigma Data Converters Reprints of Articles from IEEE publications 1962-1990, pp. 1-29.
Candy "A Use of Double Integration in Sigma Delta Modulation", IEEE Transactions on Communication, vol. COM-33, Mar. 1985, pp. 249-258.
Welland et al., "A Stereo 16-Bit Delta-Sigma A/D Converter for Digital Audio", Journal of Audio Engineering Society vol. 37 No. 6, Jun. 1989 pp. 476-485.

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