Design of analog blocks for low-voltage switched systems

Design of low-voltage CMOS analog circuits becomes particularly critical when switches are involved. To drive them into the on-state a gate voltage which is higher (or lower) than the handled signal by at least the threshold voltage is required. This strongly reduces the signal swing allowed. To overcome this problem a novel approach, the “switched” operational amplifier, has recently been proposed. The idea is very interesting but it suffers from a number of practical problems. In this paper we discuss existing solutions and we suggest a new implementation. Moreover, we propose a new approach, the “switched” unity gain amplifier and we discuss the implementation of switched capacitor building blocks with this solution. Finally, we present simulation results for the proposed circuits and provide some design guidelines