Two-Port Analysis of SC Networks with Continuous Input Signals

Abstract

Switched-capacitor (SC) networks are comprised of capacitors interconnected by an array of periodically operated switches. Such networks are particularly attractive in light of the high circuit density possible with MOS circuit technology and hybrid integrated circuits using thin-film and silicon technology. Their implementation and analysis have received increasing attention over the last years, and economical designs find applications in communication and electronic equipment. Previous publications by the author and G. S. Moschytz have shown that SC networks can be analyzed as time-variant sampled-data networks by using nodal charge equations. This led to four-port equivalent circuits in the Z domain, thus modeling the SC network with a time-invariant network. The four-port equivalent circuit was reduced to a two-port, and a two-port transfer function for the entire SC network was derived. This previous work assumed that the network is fed by a staircase input function. In this paper, we show how the theory can be extended to continuous input functions. The results obtained are similar to those obtained by Liou and Kuo, but, since we use traditional two-port theory, the derivation is different. This derivation makes it simple and more intuitively accessible. The interpretation of the analytical expression leads to a bypass circuit that has the properties of a classical ring modulator added to the two-port equivalent circuit mentioned above. We present examples.