DS - 760 IEEE JOURNAL OF SOLID-STATE CIRCUITS VOL SC-13 NO...

760 IEEE JOURNAL OF SOLID-STATE CIRCUITS, VOL. SC-13,NO. 6, DECEMBER 1978
High-Performance NMOS Operational Amplifier
DANIEL S13NDEROWICZ, STUDENT MEMBER, IEEE, DAVID A. HODGES, FELLOW, IEEE, AND
PAUL R. GRAY, SENIOR MEMBER, IEEE
Abstract-A
high-performance operational amplifier 300 milz in area
has been designed and fabricated in a standard n-channel silicon-gate
enhancement/depletion MOS process. Specifications achieved include
open-loop gain, 1000; power consumption, 10 mW; common-mode range
within 1.5 V of either supply rail; unity-gain bandwidth, 3.0 MHr with
80° phase margin; rms input noise (2.5 Hz-46 kHz), 25 wV; C-message
weighted noise -5 dBmC, and O.I-percent settling time, 2.5 MS.
I. INTRODUCTION
o
PERATIONAL amplifiers are necessary elements in
LSI analog components such as charge-coupled device
filters [1], analog-to-digital converters [2], and sampled-data
recursive and state variable filters [3], [4]. This paper describes
a high-performance operational amplifier realized in a standard
n-channel silicon-gate MOS process. This amplifier offers better
performance, lower power consumption, and requires less
silicon chip area than previous designs [5].
Compared to bipolar transistors, MOS transistors exhibit
lower transconductance per unit supply current, poorer device
matching, and higher equivalent input noise levels. On the other
hand, IvlOS transistors are superior aslow-offset analog switches
and high input impedance amplifying devices. Modern MOS
processes employing local oxidation, high-resistivity substrates,
and self-aligned device structures show extremely small parasitic
capacitances and provide very high analog circuit density.
Through proper use of the analog memory capability of MOS
sampled-data circuits, the effects of device mismatching and
flicker (1 /fl noise can be greatly reduced, Overall, the per-
formance of analog LSI based on MOS technology can match
or surpass that of circuits based on bipolar technology in
many applications, while providing markedly higher levels of
integration.
II. CIRCUIT REQUIREMENTS
The operational amplifier described here is intended for use
at audio frequencies. One to twenty or more amplifiers may
be incorporated
on a larger analog MOS LSI chip. An open-
loop dc voltage gain greater than 1000 is typically needed to
provide closed-loop gain accuracy on the order of 0.1 percent.
A unity-gain bandwidth greater than 2 MHz is necessary if the
Manuscript received October 1, 1977; revised July 30, 1978. This
research was supported by U.S. Army Research Office Grant DAAG29-
76-G-0244.
The authors are with the Department of Electrical Engineering and
Computer Sciences, University of California, Berkeley, CA 94720.
amplifier is to be useful throughout the audio frequency range.
This requirement was to be met with internal phase compensa-
tion adequate to assure stability under all conditions. It was
desired that the output be capable of driving at least 1 V rms
into a 1000-C? external load, and 2 V rms into a high-im-
pedance load, but quiescent dc power consumption was required
to be less than 20 mW. Common-mode rejection