Efficient low-power designs using MOSFETs in the weak inversion region

The availability today of process technologies such as submicron CMOS and BiCMOS allow circuit designers to push the limits of circuit performance. However, this is only possible when designers are fully equipped with good understanding of such device operation. In very low power applications, the use of MOSFETs operating in the weak inversion region is very attractive. Nevertheless, it is not easy to manipulate the devices since models such as the BSIM empirical model are complicated and involve too many parameters. As a result, hand calculation for an initial design is very difficult and can be a major obstacle for circuit designers. This paper presents an intuitive way of manipulating the weakly inverted MOSFET. An effective procedure for initial hand calculation is given, based upon simulation models and parameters. Comparisons between the calculation results and simulation results are performed to confirm the concept.