Analysis and design of a CMOS sample-and-hold circuit for biomedical applications

Abstract

A new ultra low power sample and hold circuit (S/H) has been proposed in this thesis. Taking into study of imperfections to the conventional S/H circuits, a new lowpower circuit architecture that makes use of Correlated Double Sampling (CDS) is proposed. In along with ultra low-power op-amp, the circuit can be applied for ultra lowpower biomedical applications. Circuit operation and analysis of imperfect compensation have been presented. Not only does it support rail-to-rail operation, the errors such as offset, charge injection, clock feedthrough, finite open-loop gain of op-amp are made insensitive. More importantly, based on proposed mismatch compensation technique, it is totally independent on the mismatch between capacitive components that defines the closed-loop gain of switched-capacitor amplifier for use in S/H function, making it a very useful building block for precision analog/mixed-signal applications. The transistor-level simulation results using realistic models from TSMC 0.25 um CMOS process technology, have confirmed that the structure has achieved numerous technical merits. Although the technique has the disadvantage of four-clock cycle in latency, it does not jeopardize the performance in the usual low frequency biosignals.