SLOPE ANALOG-TO-DIGITAL CONVERTER WITH RAMP INITIATED PRIOR TO COUNTER

摘要

A slope analog-to-digital converter (10) performs a conversion of the instantaneous value of a variable analog input voltage to a digital value with reduced conversion errors by starting the ramp charging prior to initiation of the counter/time/register (30). The charging capacitor (12) is first discharged to a level slightly below analog ground by a discharge reference circuit (23). The charging source (11) is then connected to the capacitor (12) to initiate the ramp voltage. When the ramp voltage passes through the ground level reference as sensed by a start count comparator (26) accumulation of counting pulses is begun. The capacitor voltage is ramped up until the level of the ramp voltage exceeds that of the analog input as sensed by a stop count comparator (27). The accumulated count constitutes a digital value corresponding to the value of the analog input. After the cumulative count is obtained the capacitor is again discharged to a level below ground in preparation for the next conversion.