A circuit for trimming a thermally-trimmable resistor, measuring a temperature coefficient of resistance of the thermally-trimmable resistor, and annealing a thermally-trimmable resistor post-trimming, the circuit comprising: a thermally-isolated area on a substrate housing the thermally-trimmable resistor; heating circuitry for applying a signal to a heating resistor; and a constant-power module adapted to maintain power dissipated in the heating resistor substantially constant over a duration of the signal by varying at least one parameter of the signal as a result of a change in resistance of the heating resistor during the signal.