A method for deriving a tracking error signal based on a first analog detection signal and a second analog detection signal. The method includes summing the first analog detection signal and the second analog detection signal to generate an analog sum signal. An analog delay device is utilized to delay the analog sum signal to be a delay signal. The delay signal is digitalized into a digital delay signal. The first analog detection signal and the second analog detection signal are respectively transformed into a first digital detection signal and a second digital detect signal. The tracking error signal is then generated utilizing a comparing operation among the digital delay signal, the first digital detect signal, and the first digital detect signal.