A signal calibration apparatus of a charge pump minimizes a current from the charge pump. The signal calibration apparatus includes a detecting circuit, a current adjusting circuit, and a calibrating circuit, wherein the detecting circuit is coupled to the charge pump for outputting a detecting signal according to the direction and magnitude of the current, the current adjusting circuit is coupled to the detecting circuit for outputting a calibrating signal according to the polarity and magnitude of the slew rate of the detecting signal; and the calibrating circuit, which consists of a first calibration current source and a second calibration current source, is respectively coupled to the charge pump and the current adjusting circuit for adjusting the first current and the second current by outputting a first calibrating current and second calibrating current to the charge pump.