Demystifying Auto-Zero Amplifiers—2

Demystifying Auto-Zero Amplifiers—2：They essentially eliminate offset, drift, and
1/f noise. Here are some design ideas.
by Eric Nolan and Reza Moghimi
Part 1 of this two-part article explains how auto-zero amplifiers
work and identifies their important characteristics. As promised,
this installment will discuss a few application ideas that are
particularly well suited to auto-zero amplifiers
Applying auto-zero amplifiers really is not much different from
applying any operational amplifier. Most new designs have the
same pinout and functionality as any other amplifier. DC closedloop
gain is set by resistors in the same manner; functions such as
filtering, integration, and the like can be done in the same way. In
most applications, the principal accommodation will be limiting
the bandwidth to exclude the chopping noise and IMD artifacts
from the passband. For auto-zero amplifiers with fixed-chopper
frequency, this generally limits their application to dc or lowfrequency
signals below 1 or 2 kHz.
PRECISION CURRENT SHUNTS
A precision shunt current sensor benefits by some of the unique
attributes of auto-zero amplifiers used in a differencing
configuration (Figure 1). Shunt current sensors are used in
precision current sources for feedback control systems. They are
also used in a variety of other applications, including battery fuel
gauging, torque feedback controls in electric power steering and
precision power metering.