A reference voltage generator includes a detecting voltage provider, a comparator, and a core circuit. The detecting voltage provider provides a detecting voltage with a first voltage level corresponding to a voltage coefficient. The comparator compares the first voltage level of the detecting voltage with a plurality of sampled amplitudes of an input signal to respectively generate a plurality of comparison results. The core circuit is used to: collect a plurality of first comparison results associated with a current received bit of a preset value from the comparison results; take the voltage coefficient as a first boundary voltage coefficient in response to the first comparison results satisfying a first condition; take the voltage coefficient as a second boundary voltage coefficient in response to the first comparison results satisfying a second condition. The reference circuit generates a reference voltage according to the first and second boundary voltage coefficients.