A digital-to-analog converter circuit generates an analog transmitted signal according to a digital transmitted signal. A first echo canceller circuit generates a first echo cancelling signal according to the digital transmitted signal. A processor circuit generates an analog processed signal according to the analog transmitted signal, the first echo cancelling signal, and a received signal. An analog-to-digital converter circuit generates a digital value according to the analog processed signal and two slicer levels of a plurality of slicer levels. A storage circuit stores a look-up table. The look-up table records an offset value corresponding to the digital value. The storage circuit further outputs a first output signal according to the digital value and the offset value. The offset value is updated according to an error value associated with the first output signal.