A signal processing apparatus includes a first signal processing circuit and the second signal processing circuit. The first signal processing circuit receives a first signal. The first signal processing circuit has a power end connecting to a first voltage and a reference ground end. The second signal processing circuit receives a second signal. The second signal processing circuit has a power end which is electrically coupled to the reference ground end of the first signal processing circuit or equals the reference ground end of the first signal processing circuit. The second signal processing circuit has a reference ground end connecting to a second voltage.