An input receiver includes a first current source circuit, a second current source circuit, a first rail-to-rail amplifier circuit, a first inverter circuit, and a second inverter circuit. The first current source circuit adjusts an operating current flowing through a first node according to a first bias signal. The second current source circuit adjusts a ground current flowing through a second node according to a second bias signal. The first rail-to-rail amplifier circuit and the first inverter circuit are connected in parallel between the first node and the second node. The first rail-to-rail amplifier circuit receives an input signal and compares the input signal with a reference voltage and accordingly outputs an amplified signal. The second inverter circuit is coupled between an operating voltage and a ground voltage. The second inverter circuit generates an output signal according to an inverted signal outputted by the first inverter circuit.