A digital background calibration circuit including a digital random number generator, an analog-to-digital converter (ADC) and a plurality of switches is provided. The digital random number generator is configured to generate a first digital sequence having a plurality of bits. The ADC includes a plurality of sampling capacitors. The switches receive the first digital sequence and are coupled to the sampling capacitors. During a calibration period, the digital random number generator controls the sampling capacitors via the switches to sample the first digital sequence.