This preview shows pages 1–2. Sign up to view the full content.
T.H Lee
EE214
IC OpAmps Through the Ages
©2000 Thomas H. Lee, rev. October 17, 2004; All rights reserved
Page 1 of 34
IC OpAmps Through the Ages
1.0
Introduction
The operational amplifier concept emerged from extensive development of electronic ana
log computers in the 1940s. Operational amplifiers get their name from their ability to per
form mathematical operations such as summation, integration and differentiation. With
the addition of logarithmic amplifiers and feedback, one may perform multiplication and
division as well. These abilities allow opamp circuits to simulate differential equations,
such as those describing the trajectory of an aircraft, for example. Countless analog com
puters were used throughout the second world war to produce “smarter” weapons capable
of predicting where a target would be some time in the future, to determine the optimal fir
ing conditions to ensure with high probability that a shell would intercept it then. The abil
ity to “program” an analog computer rapidly by changing amplifier gains and connectivity
made it an indispensable tool for both weaponry and academic research. Mechanical ana
log computers had preceded electronic ones, and changing gears and linkages made repro
gramming a cumbersome affair.
The desire for compactness and universality led to the development of generalpurpose
high gain blocks intended for use within a feedback loop, the opamp idea that is “obvi
ous” today. Perhaps the most famous opamp of the vacuum tube era was the Philbrick
K2W, whose particularly elegant design served as the inspiration for transistorized coun
terparts throughout the 1950s and 1960s.
Early efforts at integrated circuit opamps attempted to replicate on a onetoone basis the
connectivity of earlier discrete designs. These pioneering efforts led to impractical results,
for the reasons we’ve discussed numerous times: IC technology offers a different set of
strengths and weaknesses, and these different rules (should) result in different design
approaches. Early IC opamps, practical or not, were first implemented in bipolar technol
ogies, and it is in those technologies that many nowfamiliar topologies debuted. The col
lection of opamp schematics here traces that history in order to gain an appreciation for
why IC opamp topologies are what they are. Even though these are mainly bipolar exam
ples, a great many of these topologies are perfectly amenable to implementation in CMOS
form as well, with appropriate modifications (e.g., for biasing, etc.). At the very least,
these examples may serve as a valuable source of inspiration for new designs.
The dates that follow the part numbers correspond to the first year of publication of a
paper or data sheet, or the first year of product shipment.
This preview has intentionally blurred sections. Sign up to view the full version.
View Full Document
This is the end of the preview. Sign up
to
access the rest of the document.
This note was uploaded on 04/17/2008 for the course EE 214 taught by Professor Murmann,b during the Fall '04 term at Stanford.
 Fall '04
 Murmann,B
 Amplifier, Integrated Circuit, Operational Amplifier

Click to edit the document details