In a circuit with resistance, inductance, and capacitance, the obstruction to alternating current is called impedance. Impedance is commonly represented by Z, is a complex number, the real part is

called the resistance, the imaginary part is called the reactance, where the capacitor in the circuit to the AC obstruction is called the capacitive reactance, the inductance in the circuit to the AC

obstruction is called the inductive reactance, capacitance and inductance in the circuit to the AC caused by the obstruction is called the reactance. The unit of impedance is ohms.

(1) Characteristic impedance

In electronic information products such as computers and wireless communications, the energy transmitted in the PCB line is a square wave signal (square wave signal, called pulse) composed of

voltage and time, and the resistance it encounters is called the characteristic impedance.

(2) Differential impedance

The driving end inputs two identical signal waveforms of opposite polarity, respectively transmitted by two differential lines, and the two differential signals are subtracted at the receiving end. The

differential impedance is the impedance between the two lines.

(3) odd mode impedance

The impedance of one line of the two lines to the ground Zoo, the impedance values of the two lines are the same.

(4) even mode impedance

The driving end inputs two identical signal waveforms of the same polarity, and the impedance Zcom when the two lines are connected.

(5) Common mode impedance

The impedance of one line to the ground in the two lines is Zoe, and the impedance values of the two lines are the same, usually greater than the odd-mode impedance.