Sigma-delta modulator with improved tone rejection and method th

Details Sigma-delta modulator with improved tone rejection and method th Sigma-delta modulator with improved tone rejection and method th

1993-03-22

1994-10-18

Williams, Howard L.

Coded data generation or conversion

Analog to or from digital conversion

Differential encoder and/or decoder

341 76, H03M 300

Patent

active

053572521

ABSTRACT:
A sigma-delta modulator (50, 100) attenuates a frequency domain characteristic of a feedback signal to a first stage (60) of the modulator (50, 100) near f.sub.s /2, where f.sub.s is the modulator's (50, 100) clock frequency. The modulator (50, 100) thus virtually eliminates in-band tones which are characteristic of known sigma-delta modulators, without complex dithering schemes. In one embodiment, the sigma-delta modulator (50, 100) includes a two-tap finite impulse response (FIR) filter (80) within a feedback loop of the modulator (50, 100). The two-tap FIR filter (80) smoothes transitions at an output of a second stage (70) to provide the feedback signal to the first stage (60). This architecture is useful for either a digital-to-analog sigma-delta modulator (50) or an analog-to-digital sigma-delta modulator (100).

REFERENCES:
patent: 4876543 (1989-10-01), van Bavel
patent: 5057840 (1991-10-01), Ledzius et al.
patent: 5073778 (1991-12-01), Ueki et al.
patent: 5134402 (1992-07-01), Miyoshi

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