A delta-sigma modulator includes a receiving circuit, a loop filter module, a quantizer, a delta-sigma truncator, a digital filter module, and an output circuit. The receiving circuit is arranged for receiving a feedback signal and an input signal to generate a summation signal. The loop filter module is arranged for filtering the summation signal to generate a filtered summation signal. The quantizer is arranged for generating a first digital signal according to the filtered summation signal. The delta-sigma truncator is arranged for truncating the first digital signal to generate a second digital signal. The digital filter module is arranged for filtering the first digital signal and the second digital signal to generate a filtered first digital signal and a filtered second digital signal, respectively. The output circuit is arranged for generating an output signal according to the filtered first digital signal and the filtered second digital signal.