Calibration; Figure 145. Calibration Timing Diagram - ST STM32F101 Series Reference Manual

RM0008
16.5

Calibration

The ADC has an built-in self calibration mode. Calibration significantly reduces accuracy
errors due to internal capacitor bank variations. During calibration, an error-correction code
(digital word) is calculated for each capacitor, and during all subsequent conversions, the
error contribution of each capacitor is removed using this code.
Calibration is started by setting the CAL bit in the ADC_CR2 register. Once calibration is
over, the CAL bit is reset by hardware and normal conversion can be performed. It is
recommended to calibrate the ADC once at power-on. The calibration codes are stored in
the ADC_DR as soon as the calibration phase ends.
Note: 1 It is recommended to perform a calibration after each power-up.
2 Before starting a calibration the ADC must have been in power-off state (ADON bit = '0') for
at least two ADC clock cycles.

Figure 145. Calibration timing diagram

CLK
CAL
ADC
Conversion
Calibration ongoing
t
CAL
Analog-to-digital converter (ADC)
Calibration Reset by Hardware
Normal ADC Conversion
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