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PCB track impedence matching problem

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mahenreddy

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pcb track

If trace impedance is higher than the impedance of the driver, a series termination resistor is needed at the output f the driver. How do we solve if the impedance of the driver is more than the impedance of the trace?

Besides other parameters does the material used for PCB fabrication (not the one used to draw traces) affects the trace impedance?

Is there any formula or guideline that tells when to add termination resistor?

TIA

-m
 

dmd4raj

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50 ohm pcb trace

Hi...
Most of the CMOS ICs will have High Input Impedance (10^12 ohms) and very low output impedance(10-20 ohms).To match these impedance with the trace impedance (Series termination of 30 or 33ohm at source(33+20(Ic o/p imp)=53)) and parallel termination(50ohms )@ driver to reduce the input impedance of the IC from the order of 10^12 ohms(paralleling 50 ohms and 10^12 ohms will yield 50 ohms)to 50 ohms.

Regards
Rajan.k
 
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