Admittance Parameters or Y Parameters

In the case of impedance parameter or Z parameter we express voltage in the term of current by the following equations.

Similarly, we can represent current in terms of voltage bt admittance parameters of a two port network. Then we will represent the current voltage relations as,

This can also be represented in matrix form as,

Here, Y11, Y12, Y21 and Y22 are admittance parameter. Sometimes these are called as Y parameters.
We can determine the values of the parameters of a particular two port network by making short-circuited output port and input port alternatively as follows.
First let us apply current source of I1 at input port keeping the output port short circuited as shown below.

In this case, the voltage across output prt will be zero since the terminals of the port is short circuited.

Now, the ratio of input current I1 to input voltage V1 while output voltage V2 = 0, is

This is called short circuit input admittance.
The ratio of output current I2 to input voltage V1 while output voltage V2 = 0, is

This is referred as short circuit transfer admittance from input port to output port.
Now, let us short circuit the input port of the network and apply current I2 at output port, as shown below.
apply current output port
In this case,

This is called short circuit output admittance.

This is called short circuit transfer admittance from input port to output port.
So finally,

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