10.1 Introduction

An important area of application of analogue circuits is for the realisation of high precision integrated circuit filters. In Chapter 9, design techniques have been presented for high frequency state-of-the-art continuous-time filters implemented in CMOS technology. This present Chapter attempts to generalise on the realisation of monolithic filters, using a common framework based on the transconductor element, which encompasses many switched capacitor and integrated continuous-time filter realisation architectures. We focus particularly on the distinction of whether voltages or currents are used as the simulating variables, or charges in the switched capacitor case. Although the adoption of current processing will almost certainly eventually lead to filters with very high operating frequencies ^[1 ^, 2 ^], and we are beginning to see this process starting already, in this Chapter we confine our scope to examining the benefits of current processing from the points of view of minimising sensitivity of response to component parameter variations and also maximising signal handling capability.

Current conveyors have already been used to realise biquadratic active RC filter sections [3]. However, for high order monolithic filters, with which we are concerned in this Chapter, the method of cascading biquadratic sections leads to unacceptably high sensitivity of the response to component parameter variations. Consequently, we use the general method of simulating low sensitivity LCR filters. The simulating filters derived will be described and analysed using two alternative approaches which have specific features.

In one approach, we derive a signal flow graph representation of...