Impedance detecting device and method

An impedance detecting device capable of detecting the impedance value of a load, comprising:

• an alternating current (AC) signal generating circuit operable to generate an AC signal;
• an output buffer operable to generate an output voltage and an output current according to the AC signal and the impedance value of the load;
• a current mirror operable to generate a mirror current according to the output current;
• a detection impedance operable to generate a detection voltage according to the mirror current;
• a comparing circuit operable to generate a comparison result by comparing the output voltage with the detection voltage;
• and
• a control circuit, coupled to the comparing circuit and at least one of the current mirror and the detection impedance, operable to adjust at least one of a current ratio of the mirror current to the output current and the impedance value of the detection impedance according to the comparison result until the comparison result has satisfied a predetermined requirement.