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A monolithic sigma-delta A/D and D/A converter with filter for broad-band speech coding


IEEE journal of solid-state circuits 26 (1991), No.12, pp.1920-1927
ISSN: 0018-9200
Journal Article
Fraunhofer IMS ()
A/D converter; CCITT G.722; CODEC; Sigma-Delta Modulation

In this paper we present a 5-V-only, 14-b, 16-ksamples/s linear CODEC suitable as the audio part of a CCITT G722 CODEC. The device uses second-order Sigma-Delta modulation for both A/D and D/A conversion at 2.048 Msamples/s. A time-continuous modulator with integrated antialias filtering is used at the A/D side, obviating the need for an external antialiasing filter. The digital filters for decimation and interpolation are implemented with both a custom DSP and specialized hardware. The device was realized with 74 000 transistors on a 31-mmü die in a 3-fm SACMOS technology. A dynamic range of more than 80 dB and a passband ripple of 0.3 dB were attained with A/D and D/A paths in cascade.