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An equivalent impedance is an equivalent circuit of an electrical network of impedance elements [note 2] which presents the same impedance between all pairs of terminals [note 10] as did the given network. This article describes mathematical transformations between some passive, linear impedance networks commonly found in electronic circuits.
The power dissipation of the Thévenin equivalent is not necessarily identical to the power dissipation of the real system. However, the power dissipated by an external resistor between the two output terminals is the same regardless of how the internal circuit is implemented.
In electrical engineering, impedance is the opposition to alternating current presented by the combined effect of resistance and reactance in a circuit. [1]Quantitatively, the impedance of a two-terminal circuit element is the ratio of the complex representation of the sinusoidal voltage between its terminals, to the complex representation of the current flowing through it. [2]
It can be shown that four such parameters are required to fully characterise the two-port network. These could be the forward transfer function, the input impedance, the reverse transfer function (i.e., the voltage appearing at the input when a voltage is applied to the output) and the output impedance.
The equivalent circuit for Z-parameters of a two-port network. The equivalent circuit for Z-parameters of a reciprocal two-port network. The Z-parameter matrix for the two-port network is probably the most common. In this case the relationship between the port currents, port voltages and the Z-parameter matrix is given by:
Norton equivalent – Any linear two-terminal circuit can be replaced by a current source and a parallel impedance. However, the single impedance can be of arbitrary complexity (as a function of frequency) and may be irreducible to a simpler form.
The input impedance of an infinite line is equal to the characteristic impedance since the transmitted wave is never reflected back from the end. Equivalently: The characteristic impedance of a line is that impedance which, when terminating an arbitrary length of line at its output, produces an input impedance of equal value. This is so because ...
The relationship between the characteristic impedance, Z 0, input impedance, Z in and load impedance, Z L is: = Alternatives to the quarter-wave impedance transformer include lumped circuits that can produce the impedance inverter function, and stubs for impedance matching.