Unwanted electrical energy in a circuit that is unrelated to the desired signal, S-ources of noise are most often generated by some type of switching circuit,Common sources include switching voltage regulators and clocked sighals such as digitol crcuits.

• 指在一电路中与所要讯号无关的多余电能，杂讯的来源通常为某些形式的切换电路，常见的杂讯为切换式电压，调整器及时脉讯号，如一些数位电路。