With a constant dc input, the output of the AD719x ADC drifts with temperature. Why?
The performance of any ADC varies with temperature. When a calibration is performed at a temperature, the offset error and gain error are minimized at the temperature at which the calibration is performed. However, the offset error and gain error vary with temperature. For example, if you short the analog inputs to some voltage such as the reference voltage and perform a calibration, the peak-to-peak resolution given in the datasheet for the specific output data rate and gain should be met. If the temperature varies, the ADC output will vary as the offset error and gain error have drifted with temperature. These drifts are specified in the datasheet.
There will also be drift in the remainder of the signal chain. For example, the reference voltage will vary with temperature also. This variation is specified in the voltage reference datasheet. Resistance values also will vary with temperature. Therefore, it is important to use an accurate reference that has low drift along with resistors with tight tolerances. Solder joints on a circuit board will also have thermal qualities. Each solder joint connects two dissimilar metals which generates a small thermocouple. Therefore, signal paths for analog signals such as the analog inputs should be kept identical. This will ensure that affects outside the ADC on the analog input lines due to temperature variation are matched and will be removed as a common mode affect.
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