A temperature-to-digital converter is described which uses a sensor based on the principle of accurately scaled currents in the parasitic substrate p-n-p in a standard fine-line CMOS process. The resulting PTAT /spl delta/V/sub BE/ signal is amplified in an auto-zeroed switched-capacitor circuit, sampled, and converted to a digital output by a low-power 10-bit SAR ADC providing a resolution of 0.25/spl deg/ from -55/spl deg/C to 125/spl deg/C with an error of less than 1/spl deg/. A single adjustment of temperature error is provided for wafer probe. No further calibration is required. A switching bandgap reference circuit will also be described which uses similar techniques to generate an accurate low-noise reference voltage for the ADC. The circuits are part of a multichannel data-acquisition system where other input voltages must also be sampled and measured, and so the speed and power of the ADC is not determined by the temperature sensor alone. For continuous operation, the supply current is 1 mA, but a low-power mode is provided where the part is normally in shut down and only powers up when required. In this mode, the average power supply current at 10 conversions/s is 0.3 /spl mu/A. The supply voltage is 2.7-5.5 V.