QSCsim A Circuit Simulator for Switched Capacitor Circuit Analysis

Abstract

Many signal processing functions in modern-day digital communication systems are performed on discrete samples of the continuous-time input signal. These systems combine the process of sampling with signal processing functionalities. Such analog discrete-time systems are widely developed using periodic time-varying circuits like switched capacitor (SC) circuits. These circuits consisting of capacitors and switches operate on the principle of charge distribution between capacitors through switches operating based on non-overlapping clock pulses. Therefore, any analysis on SC circuits should necessarily involve charge level evaluation to have a proper understanding of these circuits in the time domain. Moreover, unlike analog filters, filters constructed using the SC technique have their responses dependent only on the capacitance ratios and switching frequency thereby easing the requirement of precise components for better filter characteristics. Hence, in addition to time domain analysis, frequency domain analysis of these circuits would be a beneficial one. The capacitors and switches controlled by clock phases in SC circuits enable easy on-chip implementation using MOS technology, where analyzing the thermal noise contribution of switches and sensitivity due to capacitors are also required. The direct z-domain transfer function of SC filter circuits would be helpful in the study of pole and zero locations of the circuit. Addition ally, stability investigation would also be required as it is the major cause of concern in higher-order filters. Many CAD tools have been proposed for the different analysis of SC circuits. Among them, apart from the commercial tool SpectreRF and DIANA, most of the circuit simulators support only specific analyses on SC circuits and many including DIANA are currently unavailable for use by the researchers.