Using Ion/Ioff to predict switch-based circuit accuracy in an extended temperature range up to 300°C

In a top-down design approach sensible decisions about system architecture are hard to make unless one can obtain reasonable predictions about the performance of building blocks such as ADCs or amplifiers. When an extended temperature range up to 300°C is targeted the problem is exacerbated by the large variations in device characteristics over temperature. A fundamental choice to be made is if and where to employ discrete-time (DT) rather than continuous-time (CT) techniques. In making this choice it must be considered whether transistor switches can be implemented well enough to allow the desired precision to be achieved. The Ion=Ioff figure of merit provides a good measure of the quality of transistor switches, in this paper derivations are made which map this figure of merit to a rough prediction about the precision achievable using DT circuitry. It is found that such techniques face significant problems at high temperatures, some possible block-level architectural techniques are suggested which may be able to expand the temperature range in which DT approaches are applicable.