How is internal calibration implemented on the AD719x family of devices?
For calibration to occur regardless of which calibration mode is used on the selected channel, the ADC’s on-chip microcontroller must record the modulator output for two different analog input conditions. These are the “zero-scale” and “full-scale” points.
With these conversions, the microcontroller can calculate the gain slope for the input to output transfer function of the converter.
In internal-calibration mode, the ADC determines the calibration points internal to the ADC.
The zero-scale point used to determine the calibration coefficients is with both inputs shorted (i.e., AIN(+) = AIN(–) = AVDD/Gain) internally within the ADC. Signals connected to the analog input pins of the device will not affect the calibration procedure as long as they are within the common range of the input. The full-scale coefficient is determined by applying a voltage of AVDD/Gain to the modulator inputs.
The internal zero-scale and full-scale calibration modes are invoked in the AD719x by writing to the mode bits (MD2, MD1 and MD0 bits) in the Mode register.
In internal zero-scale calibration mode, the shorted inputs node is switched in to the modulator and a conversion is performed. When internal full-scale calibration is selected, the AVDD/Gain node is switched in and a conversion is performed.
/RDYcan be used to determine when the calibration is complete. /RDY goes high on the initiation of the calibration and returns low when the calibration is complete.
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