Patent ID: 7532028

Claim:
An impedance matching circuit, comprising: an input terminal, for receiving an input signal; a variable impedance unit, coupled to the input terminal, having an equivalent impedance for providing an input impedance at the input terminal; a signal quality evaluating unit, coupled to the input terminal, for evaluating a signal quality of the input signal; and a control unit coupled to the variable impedance unit and the signal quality evaluating unit, for outputting a control signal according to an evaluating result of the signal quality evaluating unit to adjust the equivalent impedance of the variable impedance unit, wherein the control unit comprises: a variable impedance device, having a first terminal and a second terminal, the first terminal coupled to a first predetermined potential; a control device, coupled to the signal quality evaluating unit and the variable impedance device, for selling an impedance value of the variable impedance device according to the evaluating result; a detecting unit, coupled to the second terminal, for providing the second terminal with a second predetermined potential to detect a current passing through the variable impedance device, and generating a plurality of reference voltages according to the current; and a comparing unit, coupled to the detecting unit, for comparing the reference voltages to generate a comparing result, and outputting the control signal according to the comparing result to set the equivalent impedance of the variable impedance unit.