A notch filter 100 includes a varistor 1 that is connected between a signal line SL and a ground G. The varistor 1 has a capacitive component and outputs a signal with a second frequency different from a signal with a first frequency flowing in the signal line SL and a signal with the second frequency superimposed on the signal line SL to the ground G.

A filter includes a first low-pass filter and a second low-pass filter. The first low-pass filter is located at a first channel, and includes a first resistor array coupled with a complex-signal input terminal. The second low-pass filter is located at a second channel, and includes a second resistor array coupled with the complex-signal input terminal. The complex-signal input terminal is configured to provide complex signals to the first channel and the second channel. The filter further includes a third resistor array and a fourth resistor array. The third resistor array is cross-coupled between the first low-pass filter and the second low-pass filter. The fourth resistor array is coupled between the complex-signal input terminal and the third resistor array. The first resistor array, the second resistor array and the fourth resistor array include variable resistors.