A mixed signal device having an analog-to-digital converter (ADC) with offset and gain calibration using internal voltage references whereby the digital processor calibrates out offset and gain errors in the analog-to-digital converter by adjusting the analog input amplifier gain and offset or with software compensating the digital representations of the voltages measured. Two different known voltage values are used in determining the offset and gain adjustments needed to calibrate the ADC against the two know voltage values. The mixed signal device may further comprise a Bandgap voltage reference having an accurate known voltage value. Wherein the Bandgap voltage reference may be used for further offset and gain calibration of the ADC to produce substantially absolute voltage values.