Achieving Invariability in Analog Circuits Operating in Extreme Environments

This chapter discusses some of the problems that can occur in the context of high variability and extreme environments for analog circuits, and some of the techniques that can be applied to resolve them. It introduces some interesting techniques for the reduction of variability generally, and a useful online calibration technique that offers the possibility of longer-term tolerance to variation and environmental conditions using configurable analog transistors. The key problem is the basic intrinsic variability of individual transistors. In the case of analog circuits, the impact of variability can be complex due to a large number of performance specifications. Mismatch variation can typically be lowered by careful layout of the matching devices by using standard techniques such as common centroid layout. By dynamically deriving the body bias voltage from circuit parameters, the technique can also be employed to increase robustness of the circuit against device parameter or bias condition variation.