2.1 Introduction

The MOSFET-C design technique [1 11] was introduced in 1983 [1] as a simple and effective method for integrating high complexity continuous-time filters on a single CMOS chip with large dynamic range and accurate frequency response. Prior to this invention, precision fully integrated analogue filters for communications, mass storage, consumer electronics and other applications, were realised either with sampled-data circuits such as switched capacitors [12] or with open-loop active blocks operating in continuous time such as g _m-C circuits (see Chapter 1 or References 8, 9 and 12 and the many references therein). The switched-capacitor technique required no filter tuning, ensured excellent precision in the frequency response, and yielded high dynamic range, but required the use of additional continuous-time input antialiasing filters and output smoothing filters. In addition, although switched-capacitor filters have been extremely successful in numerous low frequency applications, they are difficult to apply at high frequencies due to signal sampling. The original open-loop active-block approach was proposed for easier high frequency designs based on continuous-time operation but required on-chip tuning and suffered from excessive nonlinear effects and noise. Despite advances, these filters still have a substantially lower dynamic range than necessary in many applications [10]. MOSFET-C filters demonstrated continuous-time operation coupled with very high dynamic range. This prompted their introduction in IC products such as disk drive and consumer electronics chips.

The unique feature of MOSFET-C circuits is their fundamental similarity and first-order equivalence to certain important classical active-RC topologies. These...