AN4207

Overview of 16-bit SDADC

Doc ID 023945 Rev 1

11/28

2.1.4

Calibration

In order to get the best performance from the SDADC two parameters should be calibrated.

These parameters are offset and gain.

Offset calibration

The offset error is a constant value that is added to the ideal conversion value.Figure 6

illustrates the offset error.

The SDADC embedded in STM32F37x/38x devices provides automatic offset calibration

without adding external components. Its principle can be summarized in the following steps:

1.

Short internally both channel inputs (positive and negative)

2.

Perform conversion and store result in internal register (configuration register)

3.

Subtract automatically the calibration value from conversion value during standard

conversion.

Note:

It is recommended to run calibration at least once after SDADC configuration

Figure 6.

Offset error in SDADC

Gain calibration

Another error source is the gain error. As illustrated in Figure 7 the gain error is the deviation

of the SDADC’s transfer function from the ideal straight line. It is due to the built-in

programmable amplifier. According to the device datasheet the typical analog gain error is

-2.7% which means there can be 884 counts (at maximum voltage) due to gain error. So

reducing the gain error is mandatory when performing accurate measurements.

Analog input

Negative offset

1

2

Digital value

Positive offset

Null offset

MSv31132V1