Signal Processing and Integrated Circuits

Chapter 15

Design of Microelectronic Switched-capacitor Filters

15.1 Introduction

The earliest filters to be firmly established in the electronic design repertoire were passive ones [13, 14] employing inductors, capacitors and transformers. These have become reference designs against which any other category of filter is measured and compared. This is due to a number of reasons. First, these passive structures have been shown to be capable of satisfying the most stringent specifications that may be encountered in all disciplines of electrical engineering design. Secondly, they have been found to possess low-sensitivity properties with respect to variations in element values; a highly desirable attribute from the practical viewpoint. Finally, they do not consume power.

However, as the operating frequencies fall into and below the audio range, the required inductors develop severe limitations and disadvantages: they become large-valued, bulky, with low quality factors and expensive to construct. For this reason, active filters were introduced with the primary objective of overcoming the practical disadvantages of inductors at the lower end of the frequency spectrum. These employ, resistors, capacitors and active devices such as transistors or Op Amps, as detailed in Chapter 3 where active structures which imitate the low sensitivity properties of passive models were introduced.

With the technological advances in integrated circuit design, the rather obvious step and natural tendency ...