Square wave signal is composed of two stable levels, high level and low level, with high frequency and many harmonic components. In some specific applications, such as DC- AC inverter or switching power supply, inductance components will be used in the circuit with square wave output, but this is not what the square wave signal itself needs, but to filter out harmonic components or smooth voltage/current. Square wave signal can be directly realized by switching elements (such as transistors or integrated circuits) without adding inductance elements.