IEEE Solid-State Circuits Magazine - Winter 2016 - 26

Figure 1: A CMOS filter codec (W05) used
in Nortel SL-1 PBX switches.

watched him mentor generations of
graduate students as a professor,
teacher, and advisor at Carleton.
He and his research teams have
consistently produced innovative
results of the highest quality that
have been extensively published
and recognized by peers, his academic institution, and industry as
an extraordinary body of work.
Prof. Copeland played a pivotal
role in advancing the state of the
art in digital and analog IC design
throughout his career. He first
became known to us early in our
careers through the lore and legends circulating within BNR about
his achievements in early chargecoupled device and switched-capacitor filter circuits. Those very early
efforts were undertaken as a visiting member of the scientific staff
(MSS) at BNR in 1971-1972. The
ongoing work was undertaken collaboratively with other MSSs at BNR
and led to the first switched-capacitor filter-codec, a ground-breaking
innovation in the field and for the
company [1]. Nortel (BNR's parent
company) successfully exploited
this work by manufacturing the
first filter-codec [2], [3] used in digital multiplex switching machines
(DMSs) for telephone central offices.
Our association with BNR began
at the time when filter-codec production exceeded 10 million units
annually. These filter-codecs helped
propel DMSs into becoming the
leading digital switch product in
North America and later worldwide

W I N T E R 2 0 16

and quadrupled Nortel's revenues
to over US$6 billion annually in the
mid-1980s (see the article, "Miles
Copeland's Switched Capacitor," by
Terry Caves in this issue for further
detail). The research completed by
Miles and his colleagues enabled
BNR/Nortel to dominate the international market for decades, demonstrating not only the impact of his
academic achievement but his indisputable economic impact.
In the early 1980s, BNR/Nortel's
digital switching lead was further
extended with the introduction of
PPhone, the world's first fully featured central branch exchange (centrex) phone that enabled large businesses to have all the benefits of a
virtual local telephone switch without the need for a local customerowned switch. PPhone achieved
this functionality using multiplexed
switched-capacitor filters to enable a
1-kHz signaling channel in conjunction with the analog voice. Switched
capacitors migrated further into the
product lines with the development
of a CMOS version of the earlier Nchannel MOS filter-codec (Code W05,
see Figure 1. Chips were not sold
by Nortel outside of the company,
and each IC was given a unique internal code). This chip dramatically
increased the functions integrated
with the codec and significantly reduced the power dissipation in the
Nortel SL-1 private branch exchange

Figure 2: A digital 2B + 2D Interoffice Set
Chip (X12) with switched-capacitor equalizer and decision-feedback equalization.

IEEE SOLID-STATE CIRCUITS MAGAZINE

(PBX) products, which provided local featured telephone switching to
hotels and medium- to large-size
businesses.
In 1985, BNR/Nortel rolled out the
Meridian PBX, adding data switching
in addition to voice with digital terminals that were enabled by a custom
digital line card loop chip set, codes
X11 and X12 [4] shown in Figure 2,
and a high-speed loop interface,
code X31 [5], which achieved (then)
record speed/power performance using switched-capacitor fixed and
decision-feedback equalizers. The
soon-to-be segment dominating Norstar Key Systems for highly featured
small business telephone switching was launched by Nortel in 1987
based on a new quad filter-codec and
a digital terminal chip with integrated filter-codec, coded A09 and A10
(see Figure 3), respectively.
Throughout the 1980s, switchedcapacitor analog signal processing
dominated shipments of high-volume
terminals and line cards with low
power, area efficiency, and excellent
manufacturability. Even as late as
1991, switched-capacitor implementations were effective in cost-critical,
high-volume applications. The World
Line Card chip (code B11) met all international gain, frequency response,
impedance, ringing, and loop-feed
standards using switched-capacitor
techniques. However, as silicon feature sizes decreased into the late
1980s and early 1990s, rapidly increasing digital density made digital
signal processing a more attractive
and ultimately the most cost-effective
approach. Nevertheless, switched-capacitor circuits continued to evolve,
and the Nortel Service adaptive access line card introduced in the early
1990s employed a second-order sigma-delta converter using switchedcapacitor filters to implement its noise
transfer functions.
For more than ten years, from
1980 onward, over 200 custom BNR/
Nortel mixed-signal ICs were built based
on Prof. Copeland's seminal work in
sampled-analog and switched-capacitor circuits. These devices were the

Table of Contents for the Digital Edition of IEEE Solid-State Circuits Magazine - Winter 2016