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
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