Hi:
Like Alain was saying the AD590 is trimmed for +/- 0.5 °C from actual value - so if you are trying to measure absolute temperature you cannot do any better. However,
if you are doing relative measurements (i.e. looking to measure changes with +/- 0.05 °C accuracy) you may be able to do that provided you understand ADC, Vref and amplifier limitations, component drift and PCB leakage paths. You would need a low input bias amp with as low a bias current drift as possible - an electrometer type. For the AD590 with a scale factor of 1uA/K, the resolution you are looking for is 50nA. Designing a current to voltage is not difficult - with a 100k feedback resistor 0.05 °C=5mV. - With Vref=5V your 10bit gives you an LSB=5mV and you can get about 50° max range. But keep in mind PIC doesn't really give you true 10bit digitization....
-warrier
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