Parasitic-Tolerant Component Type Switched- Capacit or Using Unity-Gain Buffers Simulation Filters

This paper describes the realization of parasitic-tolerant com- ponent simulation-type switched-capacitor filters using unity-gain buffers. Basic to the method are new switched-capacitor transconductance elements which possess the desirable property of being free from "resistive" effects due to parasitic capacitances. The absence of resistive parasitics dramati- cally lowers the overall parasitic sensitivity of filters based on these transconductance elements. The remaining small deviations in the response can be overcome by simple predistortion. Computer simulation on a sixth-order band-pass filter is presented. The results reported in this paper will be useful in the realization of high-frequency switched-capacitor filters. I. INTRODUCTION HE switched-capacitor technique has been widely used T for integrating analog filters in MOS technology. The most popular approach for the realization of biquads and ladder structures has been to use integrators based on operational amplifiers (l). The main reason for employing the operational amplifier as the active element is that its virtual ground property enables the realization of struc- tures that are insensitive to parasitic capacitances. Conven- tional op amp based filters require an amplifier gain of several thousands in order to obtain acceptable perfor- mance. This invariably limits the upper frequency of oper- ation of these filters. By using the techniques proposed recently (5)-(8), the gain requirements can be reduced to a few hundreds. This considerably enhances the high frequency capability of op amp based filters, but it may