AN1798

Calibration and linearization technique

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3.3

Firmware description

The calibration, the linearization and offset compensation are done by software. As

described in Section 3.1, the ADC conversation range, the gain and the quantum are

computed. Figure 6 shows an example flowchart of the software:

Figure 6.

Calibration firmware implementation

Configure ADC inputs to high

impedance analog inputs

Configure the prescaler

Configure the conversion mode:

Single

Start the conversion

Compute the average of the

converted value: 2.5V (ADC_MAX)

Compute the average of the

converted value: 0V (ADC_Min)

Start of calibration

Select Channel 3

Get the conversion:

Calibrated_Result_Data =

End of Calibration

Compute the unsigned value of

Conversion_Result:

Select ADC Channel 1

Select ADC Channel 0

Compute the unsigned value of

2.5V: Unsigned_MAX

Compute the unsigned value of

0V: Unsigned_Min

Compute the sweep of conversion

Compute the quantum q

Start of conversion

polling on Channel 3

Unsigned_Result - Unsigned_Min

q = 2.5V/sweep

sweep = Unsigned_MAX - Unsigned_Min

Calibration section

Get calibrated conversion results

section

Calibrated_Result_Volt =

Calibrated_Result_Data * q

Conversion_Result

Unsigned_Result

Note: The delivered software and

flowcharts are compatible with

the following hardware configuration:

Channel_0 to read the ground value

Channel_1 to read the 2.5 V value

Channel_3 to convert the signal

You can modify the hardware configuration

but then you have to change also

the software to be in line with your hardware.

Please refer to Figure 5.