A signal receiver includes a first input terminal, a second input terminal, a first transistor, a second transistor and a variable load. The first and the second transistors each include a gate electrode, a first electrode and a second electrode. The gate electrode of the first transistor is coupled to the first input signal terminal, the gate electrode of the second transistor is coupled to the second input signal terminal, and the variable load is coupled to the first electrode of the first transistor, where a resistance of the first variable load is adjusted to make a DC level at an output node of the signal receiver keep a constant value.