ADuC7060 temperature issue with primary ADC

I am using the ADuC7060 to convert an analog signal to a digital signal. I am using pins ADC0 and ADC1 for 2 independent readings. The analog signals are in the range 0 - 30 mV. The converted data looks good as long as the chip temperature stays above ~-5 C.

When the chip temperature drops below this point, the readings make a dramatic shift down and remain down while the temperature is below the threshold mentioned. While the readings are in this shifted down stage, they do not correlate to the correct readings. I have observed that the "shifted down" readings are inversely related to the power supply.

As the chip temperature rises to above the threshold, the readings will make another shift to above where the expected readings should be and then a short time later the readings will return to where they are expected to be.

Any help with this issue would be greatly appreciated.

Thank you. PDF