Just an idea: Use a bandgap. Instead of completely canceling the tempco adjust it in a way that it fits the wanted tempco. I think in a bandgap this is done by resistor ratio which can easily be reconfigured.

Regards

Hi Jiesteve,

Either the bandgap based on BJTs or sub-threshold current source, the PTAT (Proportional To Absolute Temperature) derives from a voltage difference that is PTAT. The PTAT voltage is applied on both terminals of a resistor, so PTAT current flows through the resistor. Don't forget that the resistor always has non-zero temp coeffecient whatever it is made of, like nwell, poly, and diffusion.

Nonetheless, you might make a resistor made of more than one type of material, one with positive temp coeffecient, the other with negative temp coeffecient. They are put in series or parallel. Choose the ratio of both type of material to let the the combined resistor is of zero temp coeffecient. Just try it. Good luck.

Yawei