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Impedance

the opposition of an electronic component to the flow of current, measured in ohms. Most commonly thought of as a resistor, however, all devices have impedance associated with them. In transmission lines , it is a measure of the characteristic impedance of a cable, a PCB trace or an interconnect. The impedance of a transmission line (ZO ) is defined as: ZO = √(L/C), where C = capacitance and L = inductance. As capacitance decreases or inductance increases per unit length, the impedance of the cable or connector will increase. Conversely, as capacitance increases or inductance decreases per unit length, the impedance of the cable or connector will decrease. Typical transmission lines may have impedance of 50 or 100 ohms. When the impedance of a connector is stated, the risetime of the pulse used to determine that impedance should also be stated.