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Maxim > Design Support > Technical Documents > Application Notes > Amplifiers > APP 4301
Maxim > Design Support > Technical Documents > Application Notes > Digital Potentiometers > APP 4301
Keywords: BiCMOS, IC transistors, operational amplifier, op amp, zero temperature coefficient, resistors,
precision arrays, binning, tolerance grade, bandwidth, frequency response, summing amp
APPLICATION NOTE 4301
The Zero-Transistor IC, a New Plateau in IC
Design
By: Bill Laumeister, Strategic Applications Engineer
Apr 01, 2013
Abstract: We can apply a BiCMOS integrated circuit with only resistors and no transistors to solve a
difficult design problem. The mythically perfect operational amplifier's gain and temperature coefficient
are dependent on external resistor values. Maxim precision resistor arrays are manufactured together on
a single die and then automatically trimmed, to ensure close ratio matching. This guarantees that the
operational amplifier (op amp) gain and temperature coefficient are predictable and reliable, even with
large production volumes.
A similar version of this article appeared in the March 1, 2013 issue of Electronics World magazine.
Introduction
This article explains how a BiCMOS integrated circuit with only resistors and no transistors can solve a
difficult design problem. It examines how the mythically "perfect" operational amplifier's gain and
temperature coefficient are dependent on external resistor values. It then examines some precision
resistor arrays which are manufactured together on a single die and then automatically trimmed to ensure
close ratio matching. This process guarantees that the op amp's gain and temperature coefficient are
predictable and reliable, even with large production volumes.
The Perfect and Practical Op Amp
A BiCMOS IC without transistors, that's different! Now that we have your attention, we are trying to make
a point. Why would anyone want an integrated circuit (IC) without transistors? Would anyone spend good
money for a BiCMOS mask set without transistors?
For the answers, we must visit the land of practical operational amplifier (op amp) applications. And
while there, we need to remember the old saying "a chain is only as strong as its weakest link." The
mythical, perfect, million-dollar op amp has infinite gain and a zero temperature coefficient. In Figure 1,
that perfect op amp is configured to provide noninverting amplification of an input signal.
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