Two Port Circuits

Two Port Circuits

Two port circuits in general is an analysis method ,all it says is lets put everthing in a box and forget all about the complexity and just watch the voltages and currents going in and coming out of this box.Now usually everything in the circuit is somehow related which makes the analysis possible but now that we have put an big box gap in the middle how are we going to relate the voltages and currents.

As you can see in any two port circuits only two variables are independent, the other two are dependent, which means if we have two we can find the other two dependents.

There fore there are six possible pair of equations which relate these variables together. These equations are classified by the parameters they use for relationships.

Parameters:

The port parameters are calculated using ratios, the ratios are either impedance, admittance or they are dimensionless, which means they are either voltage to voltage or current to current ratio.The parameters are usually calculated by zeroing(shorting) oneside or opening one side and calculating the ratios then doing the same on the other side. Forexample if we are looking for impedance parameters one of the sides is opened so that current is zero and ratio of V to I of other side is the parameters.

The two port parameters are grouped based on reciprocal relationships. For instance impedance and admittance are each other's reciprocal so they are classified as immittance. a and b paremeters are called the transmission parameters. g and h relate cross variables and are called hybrid parameters.

Admittance Parameters:

inorder for admittance parameters to be used in a circuit there should be NO INDEPENDENT sources within the model. The definition of admittance paramters are as follows

and solve for the equations