Design and implementation of an untrimmed MOSFET-only 10-bit A/D converter with -79-dB THD

A MOSFET-only 10-bit A/D converter is described which achieves a total harmonic distortion of up to -79 dB without trimming or calibration. The maximum conversion rate is 200 ksample/s. Implemented in a 1-/spl mu/m single-poly technology, it occupies 5.12 mm/sup 2/ and consumes 12 mW from a single 5 V supply. The MOSFET-only R-2R ladder, which is the center of the successive approximation architecture, is analyzed, and design considerations, especially the device dimensions, are given. Measurements of the linear behavior of pure MOSFET ladders are presented. The offset sensitivity of the ladder is examined, and an alternative way of summing the ladder current is suggested. A fast and effective differential current comparator is described.

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