ANALOG/DIGITAL-WANDLER MIT FENSTERDETEKTOR UND VERAENDERLICHEM TASTVERHAELTNIS

摘要

A high resolution analog to digital (A/D) converter amplifies and filters a magnitude difference between a pulse width modulated offset voltage VOFF and an input voltage VIN to produce an amplified filtered difference voltage VO, the duty cycle of offset voltage modulation being adjusted such that the magnitude of the difference voltage VO is within a narrow input voltage range of a recirculating remainder A/D converter 18. The amplified, filtered difference voltage VO is converted to digital data D1 by the recirculating remainder A/D converter 18. A microprocessor 20, which controls the offset voltage, combines the result with the magnitude of the offset voltage to produce a comparatively high resolution digital representation of the input voltage. During a first pass an autoranging circuit 12 divides the input voltage VIN by a factor of 1,000 and supplies the resulting voltage directly to A/D converter 18. in response to the output of the A/D converter 18 during the first pass the microprocessor 20 adjusts the gain of autoranging circuit 12 to provide a voltage which is a substantial portion of the input voltage range of the A/D converter 18 during a second pass. For the third pass switches S1 and S2 are closed and switch S3 opened; the offset voltage VOFF represents the output of A/D converter 18 during the second pass less a fixed non-zero amount. The output is derived from the outputs of the A/D converter 18 during the second and third passes and the gain factor supplied to the autoranging circuit 12. <IMAGE>