Merging data converters and DSPs for mixed-signal processors

The use of sigma-delta conversion to produce high resolution without using analog components such as the precise resistors in an A/D (analog/digital) or a D/A (digital/analog) converter is reported. The use of sigma-delta technology solved the problem arising from the noise levels injected into the silicon substrate during digital switching (which limited the integration of both analog and digital circuitry on one VLSI chip) and allowed the implementation of the ADSP-21MSP50, the first mixed-signal processor. The basic elements of the converter are described, and its advantages and drawbacks as well as the implications for expanded DSP applications are examined. Included in the discussion are sampling and quantization noise, modulator design, frequency-domain analysis of the modulator, the use of digital filtering to minimize shaped-quantization noise, and the higher level of integration possible with this approach.<>