A temperature sensing circuit includes a current generation circuit generating an initial current proportional to absolute temperature (Iptat), and a voltage generation circuit configured to mirror Iptat using an adjustable current source to produce a scaled current and to source the scaled current to a first terminal of a resistor to produce a reference voltage at the first terminal. A second terminal of the resistor has a voltage complementary to absolute temperature (Vctat) applied thereto. An analog-to-digital converter (ADC) has a reference input receiving the reference voltage, and a data input receiving Vctat or an externally sourced voltage. The ADC generates an output code indicative of a ratio between: a) either Vctat or the externally sourced voltage, and b) the reference voltage. A digital circuit determines a temperature readout from the output code and calibrates the reference voltage and the temperature readout determination based upon the output code.