A method of operating a memory device includes: supplying one or more supply voltages to a memory array; and monitoring the one or more supply voltages, which includes: selecting, from the one or more supply voltages, a selected supply voltage; converting, using an analog-to-digital converter (ADC), an internal reference voltage of the memory device and a scaled version of the selected supply voltage into one or more digital values; generating a calibrated measurement result using the one or more digital values; and determining whether the calibrated measurement result is within a pre-determined range.