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The formation of the PCB lead impedance interference principle

Why PCB wire can form impedance interference?

Because in the manufacture of PCB copy board, the wire is generally for copper wire, copper and the physical properties of metal determines its certain impedance, there must be in the process of conducting wire, inductance components affect the voltage signal transmission, the resistance components will affect the current signal transmission, the influence of high frequency circuit inductance is particularly prominent.

Sections of wires on the printed circuit board can be regarded as very regular rectangular copper bar, we take a 10 cm long, width 1. 5 mm, thickness of 50 microns wires, for example, can be seen by calculating the size of the impedance.

Conductor resistance can be calculated by formula:

R=ρL/s （Ω）

Type of L for the wire length (m), s for the conductor cross-sectional area (mm2), rho for resistivity rho = 0. 02, calculated the conductor resistance is about 0. 026 Ω.

When a away from other conductor wire, its length is greater than the width, the self inductance of the wire for 0. 8 mu H/m, then 10 cm long wires are 0. 08 mu H inductance. Then we can be calculated with the formulas below the copy plate conductor impedance presented by:

XL=2πfL

Type in the PI is constant, f wires through the signal frequency (Hz), L for the self inductance per unit length of wires (H). So we can respectively calculate the wire under the low frequency and high frequency impedance:

when f=10HZ, XL = 6.28×10×103×0.8×10 - 6≈0.005Ω;

when f=30HZ,XL=6. 28×30×106×0. 08×10-6≈16Ω

Through the above we can calculate the formula, its in low frequency signal transmission wire resistance is greater than the line impedance, and in the high frequency signal conductor inductance is far greater than the wire resistance.

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