Rail-to-rail comparator

The present invention discloses a rail-to-rail comparator. The rail-to-rail comparator includes: a positive voltage rail providing a positive supply voltage, a ground voltage rail providing a ground voltage, an input stage, and an output stage. The input stage includes: a positive and a negative input terminals for receiving a first input signal and a second input signal; a first differential amplifier circuit, which includes a pair of depletion NMOS transistors to generate a first pair of differential currents; and a second differential amplifier circuit, which includes a pair of native NMOS transistors to generate a second pair of differential currents. The output stage is coupled to the first differential amplifier circuit and the second differential amplifier circuit, and generates an output signal related to a difference between the first input signal and the second input signal.