IEEE Solid-State Circuits Magazine - Spring 2014 - 15

newly manufactured and deployed
around the world.
The continuing development of
switched-capacitor filter technology
drew from many contributors worldwide. The concept of using switches
and capacitors had been suggested
earlier by several authors, including
James Clerk Maxwell in 1892 [16], and
D. L. Fried in 1972 [17]. (Progress was
delayed by lack of a zero-offset electronic analog switch and an infiniteinput resistance amplifier. MOS filled
these needs.) More contemporary
with the evolution of MOS switchedcapacitor circuits, researchers from
the circuit theory and signal processing community made important
contributions, including Miles Copeland [18], Albert Fettweis [19], Gabor
Temes [20], and many others.
As silicon-gate CMOS became the
preferred technology and feature
sizes continued to shrink, analog
circuit performance improved dramatically. The availability of fast
switched-capacitor integrators, particularly in differential form, led directly
to other applications like pipeline A/D
converters, as demonstrated by Steve
Lewis [21] and Sehat Sutardja [22].
Fast switched-capacitor integrators
also enabled the later broad adoption
of sigma-delta A/D techniques. Bell
Labs and others had explored these
techniques beginning in the 1950s,
but monolithic integration in bipolar
transistor technology was difficult.
Technology scaling made sigma-delta
codecs progressively more attractive
in the 1970s. Bob Brodersen and his
students Max Hauser and Paul Hurst
were the first to apply switchedcapacitor technology to this important
class of A/D converters and associated filters [23]. In today's mobile
telephones, oversampling sigma-delta
converters followed by digital filters
have sharply reduced the requirements on analog filters before data
conversion. While the use of a high
sampling rate A/D converter followed
by digital filters was proposed in the
1970s, it became attractive in terms
of silicon area and power consumption only after major down-scaling of

device dimensions. Chip area requirements for digital circuits shrank much
more rapidly than for analog circuits
as technology scaling progressed.
In another application, MOS
mixed-signal processing was used by
Oscar Agazzi to demonstrate cancellation of nonlinear echos to meet a
need in digital subscriber loops [24].

In the early 1980s, Berkeley alumnus Asad Abidi, then at Bell Labs,
began exploring the use of scaled
NMOS technology for RF applications.
This work was the forerunner of the
later development of CMOS RF mixedsignal technology [25]. This became
one of the most important classes of
analog-digital interfaces in mobile

Figure 2: Paul Gray and Jim McCreary review the metal mask design for the chip in Fig. 1. All 5
masks were hand-cut in rubylith, then reduced photographically to final size for contact printing.

Figure 3: Fifth-order low pass ladder filter realized with switched-capacitor integrators to
meet the standard specification for digital telephony [14].

IEEE SOLID-STATE CIRCUITS MAGAZINE

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Table of Contents for the Digital Edition of IEEE Solid-State Circuits Magazine - Spring 2014