The equivalent circuit of the y parameter model

Consider the input equation of the y parameter pair:

The equation tells us that I 1 is equal to:

• a current flowing through a conductance y 11 that has a voltage V 1

across it

plus • the current generated from a current generator y 12 V 2.

y 12 is a reverse trans-conductance representing feedback from output to input.

The input equivalent circuit can be drawn as

Now consider the output equation

This equation tells us that the output current I 2 is equal to the current produced

by a current generator y 21 V 1 plus the current flowing through conductance y 22

that has a voltage V 2 across it. y 21 represents a forward trans-conductance,

often referred to as the mutual conductance.

The output equivalent circuit is now drawn as

The complete equivalent circuit can be drawn as

The parameter y 11 represents the input conductance with the output short

circuit.

The parameter y 22 represents the output conductance with the input short

circuit.

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