Integrating analog-to-digital converter having digitally-derived offset error compensation and bipolar operation without zero discontinuity

摘要

An analog-to-digital converter of the ramp-integrator type utilizing a special technique to reduce errors due to offset voltages. The integrator first is ramped up and then back to a reference level, by sequential application of opposite-polarity reference signals. A digital determination of net offset error then is made by comparing the total time of ramp-up-and-back with a fixed time period set by a clock generator. During the subsequent conversion operation, integration of the analog signal is controlled in accordance with the amount of net offset error so as to provide a feed-forward error correction. Integration is always in the same direction away from zero for analog signals of either polarity, thus avoiding the effects of discontinuity around zero input.