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In PCB / PWB boards we are following 50ohm impedance for single ended lines and 100ohm impedance for Differential lines? is it a standard value for all device input and output impedance? Each and every IC internal architecture done by millions of transistors so this impedance values determined by the IC pins connected to which pin of the transistors (BJT/FET)? Could you please help me to clarify this? thanks in advance.