"Today's increasingly
complex control
system design and
corresponding
unavoidable increase in
signal interference means
that DC precision is a
must. AC interference in
the DC signal results in
noisy readings, which can
compromise the system."
Sneha Patel
Senior Power Hardware Engineer R&D,
Rockwell Automation
Chapter Three
Optimizing for Highest DC
Precision
One of the major optimizations that engineers might desire for their precision signal chain is
achieving the highest DC precision. Precision narrow bandwidth signal chains are designed
for applications where DC precision is the highest priority, providing best-in-class accuracy,
stability, repeatability, and resolution. For the purposes here, the narrow bandwidth signal
frequency range is defined as DC to approximately 10 kilohertz (kHz).
A source measurement unit (SMU) is an example of an application for which an extremely
high level of precision is required at narrow bandwidths. SMUs are closed-loop four-quadrant
instruments with sink and source voltage and current capability, and they generate and
measure highly precise signals. At a minimum, an SMU must be fast and accurate and feature
a wide dynamic range while maintaining stability for a wide variety of load conditions. The
accuracy and quality of the instrument produced will be directly impacted by the component
selections within the SMU signal chain. Creating a highly accurate, stable, and repeatable SMU
places demanding requirements on its signal chain components. However, when tradeoffs are
correctly balanced and optimized, incredible DC precision performance can be realized. The
key accuracy specifications of an SMU are impacted by the linearity, monotonicity, glitch energy,
noise performance, and repeatability of its underlying signal chain.
13 | Optimizing for Highest DC Precision
