BiCMOS processes provide an additional bipolar device, which has been the workhorse of analog design. The bipolar transistor can be used to increase the speed, reduce the mismatch, and obtain better circuit characteristics when exponential I-V relatinship is required. However, the use of BiCMOS processes has been limited due to its complexity and cost. Also the large area required for each bipolar transistor makes them unattractive for large vision chips.