How to successfully calibrate an open loop DAC signal-chain


Any practical electronic application is subject to multiple sources of error that can make the most precise components deviate from their datasheet behavior.
When the application signal chain doesn’t have a built-in mechanism to self adjust for these errors, the only approach to minimize their impact is to measure
them and calibrate them out systematically.

An open-loop system is a system that does not use its output to perform adjusting control actions on its inputs to achieve the required performance, while in a
closed-loop system, the output depends on a control action in the system that can automatically implement corrections to improve performance. Most digital-to-analog converter (DAC) signal chains are set-and-forget type systems, where the accuracy of the output must rely on the accuracy of each block in the signal chain. A set-and-forget system is an open-loop system. For an open-loop system that requires high accuracy, calibration is most likely needed and recommended.

We’ll introduce two types of DAC signal chain calibration: the TempCal (calibration at operating temperature), which can give the best level of error correction,
and the SpecCal (calibration using specifications), which is a valid alternative
when using TempCal is not possible, but it’s not as comprehensive.

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