Hi hchanda,

For any bandgap reference, the opamp offset will contribute to the temperature inaccuracy by means of its drift. If the opamp has offset, it will have an associated drift which will degrade the reference accuracy. In order to improve its accuracy (if required) the opamp ccan be chopped (therefore the offset drift is totally eliminated).

The sigma delta contribution to temperature inaccuracy I imagine might be mostly related to the quantization noise it will introduce. According to the BW and the oversampling ratio of your SD converter, the Q noise power in the band of interest (very low frequency) will dictate the "erroR" you will have when converting such temperature reading into a digital word.

In a few words, the SD converter quantizes the analog input signal by translating it into a "pulse density". The more input amplitude the more pulses within a certain time. Since the clock is fixed, the density is quantized.

Hope this helps
tosei

The SD converter can also be single or multi-bit. In either case, the "digital word" will be obtained only after (digitally) filtering and decimating the SD output by means of a decimator.