A signal processing apparatus includes: a signal conversion circuit, for performing a signal conversion operation on a reception signal to generate a first output signal according to a first clock signal, and performing the signal conversion operation on the reception signal according to a second clock signal to generate a second output signal; an amplitude adjustment circuit, coupled to the signal conversion circuit, for calculating an amplitude value of the reception signal according to the first output signal, and accordingly adjusting an amplitude of the reception signal; and a phase adjustment circuit, for adjusting a phase of the second clock signal according to the second output signal.