We have gone with the LM94022 which give very low power consumption (6uA). The accuracy is only +/- 1.5 degrees C at 25 degrees so it will need calibration. Thank you for your suggestions and avoidance of a constant current supply. You are right that low voltage ==> higher prices.
A thermistor is a good idea. The uP I am using is the SiLabs C8051F930. The A/D full scale is 1.68V. This would require an amplifier or else the self heating of the thermistor would be high. Also I would need a precision current source. This job is quite price sensitive. Just hoping for the equivalent of a DS18B20 that runs at 1.8V.
I am looking for temperature sensor with +/- 0.5 degree accuracy at 25 degrees. The DS18B20 would do the job well, but does not work over the range of 1.8V to 3.6V. Other type such as the DS75LV, and LM94022 are not accurate enough. Digital output is preferred, but can work with analogue output. The sensor is to be built into a probe with a 2 meter connecting lead. Thank you for any suggestions.