Hewlett-packard Company

Lawrence T Jones

Joe E Marriott

James Ressmeyer

A multislope A/D converter is presented which employs a multislope integration technique enabling the use of a single comparator to detect polarity changes in the integrator output voltage. The A/D converter integrates a test signal during a run-up interval and integrates a discharging signal during the run-up interval as well as during a pre-run-down interval and a run-down interval subsequent to the run-up interval. The magnitude and polarity of the discharging signal are regulated in accordance with a switching scheme that converts circuit element mismatch error into offset measurement errors which can be eliminated by subtraction. The discharging current during the pre-run-down interval ensures that the slope of the integrator output voltage at the final polarity change is independent of test signal polarity thereby avoiding a comparator hysteresis error. A decade-run-down technique is employed during the run-down interval enabling the digital conversion to be implemented on a decade counter.

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Loveland, CO, United States of America

Lawrence T Jones