A successive approximation analog-to-digital converter includes: a comparator for comparing first and second comparison voltages from a conversion module and respectively identical to first and second input voltages, which are transmitted to the conversion module via a switch module in an ON state; and a control module for controlling the switch module and the conversion module and generating a digital output that corresponds to a difference between the first and second input voltages based on first and second comparison signals from the comparator and a clock signal. The switch module includes two switch units each having a series connection of first and second switches, and a third switch coupled to a common node between the first and second switches.