The input offset voltage of an op amp can be calibrated by using the DAC or an
external constant-voltage source in conjunction with the
ADC.
To calibrate an op amp, perform the following steps:
- Use the DAC or the external I/O pin connected to the op amp non-inverting (+) input as a
constant-voltage reference. If the DAC is used, it and its output buffer must be
enabled.
- Configure the op amp with:
- MUXPOS in the OPnINMUX register set to the selected calibration source
- MUXNEG in the OPnINMUX register set to OPnOUT, so the op amp will function as a
voltage follower
- Use the ADC to measure the voltage of the selected calibration source. This value becomes
the calibration target.
- Configure the ADC input multiplexer to select the output from OPn, then use the ADC to
measure this voltage
- Use the difference between the two ADC
measurements to determine how much the calibration register (OPnCAL) should be adjusted.
The calibration step size is found in the Electrical Characteristics section.