IEEE Solid-States Circuits Magazine - Winter 2021 - 71

In Step With Bram Nauta
Three decades of analog IC design

Almost all mobile phone brands
have in common a well-known component called the Nauta circuit. It
is for this invention that microchip
architect Dr. Bram Nauta is considered a Dutch pioneer in advanced
modern technology. This achievement emerged from his childhood
interest in electronics.
Born on 20 January 1964 in Hengelo,
The Netherlands, Nauta received his
M.Sc. degree (cum laude) in electrical
engineering (with a concentration in
bipolar metal-oxide semiconductor operational transconductance
amplifier design) from the University of
Twente, Enschede, The Netherlands,
in 1987 and his Ph.D. degree in analog CMOS filters for very high frequencies (under the supervision of Dr. Evert
Seevinck) from the University of Twente in
1991 [1]-[2]. That year, he joined the MixedSignal Circuits and Systems Department, Philips Research, Eindhoven,
The Netherlands. In 1998, he returned to
the University of Twente, where he is a
distinguished professor, heading the IC
Design Group. Since 2016, he has served
as the chair of the Department of Electrical
Engineering. His current research interests
include high-speed analog CMOS circuits, software-defined radio, cognitive radio, and beamforming [3].
All these interests began in early
primary school, when Nauta's friend
came up with an electrical diagram
of an FM transmitter, and the two
began to build the device, as amateurs in electronics. Together, they
biked to an electronics store to buy
the required materials. At first, the
transmitter did not work properly.
They eventually got it to function,
and the experience opened the door
for Nauta to learn about electronics.

He thought about going to technical
school, but his parents preferred a
more advanced secondary school.
He performed at a high level and
shortly joined a preuniversity secondary school [4].
At the University of Twente, Nauta
began studies in electrical engineering, a wide-ranging field including
robotics, sensors, software, hardware, and electronics. He soon realized that he preferred electronics
and, after completing four years of
study, decided to work toward a doctoral degree. During the pursuit of his
Ph.D., his inventions became coupled
with analog electronics, which are of
fundamental concern. " Improving the
digital part of chips is mainly a matter
of better software design. I find that
less interesting and prefer to focus
on the big problem for the advancement of chips, the analog electronics, " Nauta said. " That may sound old
fashioned, but it is superhot right
now. In the development of 5G and 6G
communications, for example, better chips are needed. The electronics
have to be fast, cost efficient, and able
to operate at high frequency " [3].
The origin of Nauta's analog IC
design can be traced to his Ph.D.
work [2]. In 1989, Nauta devised a
differential transconductor, now
called the Nauta circuit, that was
used to build an active third-order,
low-pass, elliptic analog filter with
a cutoff frequency of 110 MHz, fabricated through a 3-nm CMOS process as a monolithic chip without
any physical inductor. The trans-

FUN FACTS ABOUT NAUTA
■
He

loves surfing in California.
enjoys biking.
■
He likes trying out odd things.
■
He

Digital Object Identifier 10.1109/MSSC.2020.3035979
Date of current version: 25 January 2021

conducta nce element was also
used to emulate the inductor. The
differential transconductor, a voltage-to-current converter, consists
of six CMOS inverters, and it has
good linearity properties and highfrequency performance due to the
absence of internal nodes (an internal node has no direct connection
to either an input or output node
or to a bias or a supply node in a
circuit [1]). The elliptic analog filter,
which is based on a linear, tunable
transconductance-C integrator, can
be tuned for different cutoff frequency and quality factor values.
In particular, this invention helped
save Moore's law. After Nauta performed the proper simulation, he
aimed to build the hardware circuit by going back to the electronics store of his youth to buy the
CMOS digital inverters. The circuit
works properly for 100 kHz. Thus,
the basic idea in Nauta's circuit is
the CMOS digital inverter, which
includes two inverters at the input
nodes-one at the positive node
(Inv1) and the other at the negative
node (Inv2)-and four inverters.
The outputs of each coupled in--
verter are connected, and this common
node is attached to the positive output
nodes (Inv5 and Inv6) and the negative
output nodes (Inv3 and Inv4). Therefore, all nodes in the circuit join either
the input nodes or the output nodes.
This design can eliminate parasitic
capacitances and avoids bandwidth
limitation (theoretically infinitely fast).
The common-mode level of the output
voltages Vo1 and Vo2 is controlled by
inverters Inv3-Inv6. Inv4 and Inv5
create positive resistance, connected
between the output nodes and the
common-mode voltage level Vc. Inv3
and Inv6 inject current gm3(Vc - Vo1) in
Inv4 and current gm6(Vc - Vo2) in Inv5.

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