A signal detector includes a signal input terminal, N first resistors, (N−1) second resistors, a third resistor, M voltage-to-current units and a collection unit. A first terminal of a 1st first resistor is coupled to the signal input terminal. A first terminal of an ith first resistor is coupled to a second terminal of an (i−1)th first resistor. A first terminal of a kth second resistor is coupled to a second terminal of a kth first resistor. A second terminal of each second resistor is coupled to a reference voltage terminal. The third resistor is coupled between the reference voltage terminal and a second terminal of an Nth first resistor. Each voltage-to-current unit is coupled to a first terminal of a corresponding first resistor for converting a corresponding detection voltage to a detection current. The collection unit is coupled to the M voltage-to-current units for generating a detection signal according to at least the M detection currents.