A voltage comparator including a quantum tunneling coupled transistor and a method for tuning the voltage comparator. The comparator includes a quantum tunneling coupled transistor coupled to a resistor and is capable of operating above 10 Giga-samples-per-second or a clock rate of 10 GHz. The comparator has a low power consumption of about 1 mW excluding the power required for clock generation and independent from the sampling rate. The threshold or reference voltage of the comparator is controllable by adjusting the pulse height of the clock signal. The comparator has relatively low hysteresis estimated at about 1 mV.