A calibration apparatus includes: a first circuit arranged for generating a reference voltage with respect to a first circuit element according to a reference current flowing to the first circuit element; a second circuit arranged for generating an output voltage according to a tunable current; and an adjusting circuit for adjusting the tunable current to a target current value according to the reference voltage and the output voltage, wherein the adjusting circuit comprises: a search unit for performing a search according to a comparison result of the reference voltage and the output voltage to thereby determine a control setting; and a control unit coupled to the search unit, and for generating a control signal to the second circuit according to the control setting, and after the search unit adjusts the control setting, the search unit stops adjusting the control setting according to the comparison result.