Impedance matching circuit

One kind of an impedance matching circuit as an impedance matching between the cable and the receiver, this impedance matching circuit includes a first transistor, a second transistor, a resistor, a negative feedback control circuit, a multiplexer and a reference voltage generator. An operational amplifier, a transistor and a resistor the input end of the cable and receiver to achieve the purpose of impedance matching, and when the characteristic impedance of the cable changes, the resistance of the adjustable impedance matching circuit in the reference voltage generator and the multiplexer generating different reference voltages, and still allows the receiver input end of the cable to achieve impedance matching purposes.