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What is the significance of impedance to PCB circuit boards, and why do PCB circuit boards need impedance? This article first introduces what impedance and its types are, then it introduces why PCB circuit boards need impedance, and finally explains the meaning of impedance to PCB circuit boards. Follow the editor to learn more about it.

In a circuit with resistance, inductance, and capacitance, the obstacle to alternating current is called impedance. Impedance is often represented by Z, which is a complex number. The real part is called resistance, and the imaginary part is called reactance. The hindering effect of capacitance on alternating current in the circuit is called capacitive reactance. The hindering effect of inductance on alternating current in the circuit is called inductive reactance. The obstructive effect of capacitance and inductance on alternating current in the circuit is collectively called reactance. The unit of impedance is ohms.

**(1) Natural Impedance**

In electronic information products such as computers and wireless communications, the energy transmitted in the PCB circuit is a square wave signal (called pulse) composed of voltage and time. The resistance it encounters is called natural impedance.

**(2) Differential Impedance**

Two identical signal waveforms with opposite polarities are input at the driving end, which are respectively transmitted by two differential lines, and the two differential signals are subtracted at the receiving end. The differential impedance is the impedance Zdiff between the two wires.

**(3) Odd Mode Impedance**

The impedance value of one line to ground of the two lines is the same as the impedance value of the two lines.

**(4) Even mode Impedance**

Two identical signal waveforms with the same polarity are input to the drive end, and the impedance Zcom when the two wires are connected together.

**(5) Common mode Impedance**

The impedance Zoe of one of the two lines to the ground is the same as the impedance value of the two lines, which is usually greater than the odd mode impedance.

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