102 IEEE TRANSACTIONS ON CIRCUITS AND SYSTEMS—I: FUNDAMENTAL THEORY AND APPLICATIONS, VOL. 46, NO. 1, JANUARY 1999
Darlington’s Contributions to
Transistor Circuit Design
David A. Hodges, Fellow, IEEE
(Invited Paper)
SIDNEY Darlington’s name is well known to electronic
circuit designers. He is credited with the discovery and
initial demonstration in the early 1950’s of what ever since
has been known as the Darlington transistor pair, or simply
the Darlington transistor or Darlington pair. This episode
provides another example of Sidney’s wide-ranging technical
interests and his creativity addressed to the solution of real
engineering problems.
Early silicon transistors suffered from low values of
common-emitter current gain , and large variations of
from sample to sample. might range from to for
good samples of silicon grown-junction transistors. Given
these nonideal active elements, electronic circuit designers
had difficulty designing circuits with reasonably stable and
uniform overall gain. They badly wanted transistors with
larger current gain so negative feedback could be employed,
at the sacrifice of some circuit gain, to stabilize overall circuit
performance against variations in operating conditions and
transistor characteristics. Sid Darlington surely understood
this engineering problem at the time.
The following account of the origins of the Darlington
transistor pair is due to Professor Emeritus Filson Glanz at
the University of New Hampshire.
“Just after the transistor was invented at Bell Labs, Sid-
ney checked out for the weekend two of the few existing
transistors from the head of Bell Labs. Transistors were
not generally available and the head of the Labs kept the
few that had been made in his desk. Sidney played with
them at home on the weekend and discovered/invented
the Darlington pair. He realized that they could be put
in one package (“on one chip”), and that in fact any
number of transistors could be put in one package. The
next week he was encouraged to have the lawyers draw
up the patent application. He said it should be written
for any number in one package, but the lawyers only
wanted to do it for two—which is what was applied for.
As it turned out, if it had not been restricted to two
transistors, Bell Labs and Dr. Darlington would receive
Manuscript received May 1, 1998.
The author is with the Department of Electrical Engineering and Computer
Sciences, University of California at Berkeley, Berkeley, CA 94720-1770
USA.
Publisher Item Identifier S 1057-7122(99)00545-0.
Fig. 1. Darlington transistor pair. Resistors as shown are usually included to
reduce the switching delay when turning off a conducting pair.
a royalty on every IC chip made today! Anyway, that’s
the story he tells.”1
U.S. Patent 2 663 806 titled “Semiconductor Signal Trans-
lating Device” was issued on December 22, 1953 with Sidney
Darlington as sole inventor. The drawings from the patent
are reproduced here as an illustration on the following page.
Drawings and claims are included for both two-transistor and
three-transistor compound connections. (It seems that Sidney
struck a compromise with the lawyers.) This patent often was
cited as related art on patents issued subsequently. Online
databases available today go back only to 1971; but from
1971 to 1991, 17 subsequent patents reference this Darlington
invention. Titles of those patents indicate uses ranging from
power supplies to security apparatus to television receivers.
Fig. 1 shows a schematic diagram with transistors and
connected as a Darlington transistor pair.
The resistors shown are not essential, but are usually in-
cluded to permit independent design of bias currents and
to reduce the time required to turn off a conducting pair.
They reduce the current gain particularly at low currents. If
we neglect the current flowing in the resistors and define
the common-emitter current gain for a single transistor as
, simple analysis shows that the overall dc or low
frequency current gain for the Darlington pair is
1See http://www.ece.unh.edu/faculty/sidney/SDOther.html, June 14, 1995.
Quotation with Professor Glanz’s permission.
1057–7122/99$10.00 1999 IEEE
