There is an ever increasing trend towards putting entire systems on a
single chip. This means that analog circuits will have to coexist on the
same substrate along with massive digital systems. Since technologies
are optimized with these digital systems in mind, designers will have to
make do with standard CMOS processes in the years to come. We address
analog filter design from this perspective. Filters form important
blocks in applications ranging from computer disc-drive chips to radio
transceivers. In this book, we develop the theory and techniques
necessary for the implementation of high frequency (hundreds of
megahertz) programmable continuous time filters in standard CMOS
processes. Since high density poly-poly capacitors are not available in
these technologies, alternative capacitor structures have to be found.
Met- metal capacitors have low specific capacitance. An alternative is
to use the (inherently nonlinear) capacitance formed by MOSFET gates. In
Chapter 2, we focus on the use of MOS capacitors as integrating
elements. A physics-based model which predicts distortion accurately is
presented for a two-terminal MOS structure in accumulation. Distortion
in these capacitors as a function of signal swing and bias voltage is
computed. Chapter 3 reviews continuous-time filter architectures in the
light of bias-dependent integrating capacitors. We also discuss the
merits and demerits of various CMOS transconductance elements. The
problems encountered in designing high frequency programmable filters
are discussed in detail.
