Approximation analog-to-digital converter, calibration method used in approximation analog-to-digital converter, and corresponding calibration circuit

An approximation analog-to-digital converter includes a calibration mode and an A/D conversion mode, and includes a capacitor array including multiple capacitors, a calibration capacitor, and a calibration circuit. The calibration circuit controls output of a reference voltage to the capacitor array, adjusts a calibration voltage under the calibration mode based on the calibration capacitor to compare capacitor(s), records digital code(s) corresponding to the adjust calibration voltage, and determines transition threshold(s) according to the digital code(s) so as to compensate or correct the output bits of an input voltage in digital domain.