Chapter 23 Summary: Transmission Line Properties That Affect Impedance Chapter 23 examines the four variables that determine the impedance of a transmission line on the surface layer of a PCB. Once these are understood, it is possible to determine which features in a PCB will have a meaningful effect on impedance, including a lack of terminations, changes in trace width in the same layer, connector transitions and loads along the transmission line. Readers will learn that the two biggest causes of impedance mismatch are poorly matched terminations and changes in characteristic capacitance.
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