I am trying to find the ABCD parameters of the two port network in this circuit (where \$R = 1\Omega\$ and \$x = 1\$):


simulate this circuit – Schematic created using CircuitLab

To determine A and C, we leave the output port open so that \$I_2=0\$ and place a voltage source \$V_1\$ at the input port. We have

\$V_1 = (j10 + 1)I_1\$


\$V_2 = I_1 * \$ what?

Should I do this with nodal analysis instead?


2 Answers 2


Using the definition:

$$ A = \frac{v_i}{v_0}\mid i_0=0 $$ $$ B = \frac{v_i}{i_0}\mid v_0=0 $$ $$ C = \frac{i_i}{v_0}\mid i_0=0 $$ $$ D = \frac{i_i}{i_0}\mid v_0=0 $$

Output voltage is voltage over R $$ A: v_0 = \frac{R}{R+jx}v_i \Rightarrow A = \frac{R+jx}{R} \\ $$ Input voltage is voltage over jx + voltage over R $$ B: v_i = i_ijx + (50+1)*i_iR = i_0\frac{jx}{50} + i_0\frac{51}{50}R $$ $$ v_i = \frac{jx+51R}{50}i_0 \Rightarrow B = \frac{jx+51R}{50} $$ Output voltage is voltage over R $$ C: v_0 = i_iR \Rightarrow C = \frac{1}{R}$$ Relation is already given $$ D: i_0 = 50i_i \Rightarrow D = \frac{1}{50} $$

Assuming that when $$i_0 = 0 $$ the current source cannot deliver any current.


You can not leave the terminals of a current source open.

A current source will always try to develop a voltage across its terminals so as to supply a constant current to the load. When the terminals are left open, the voltage that should be developed by the current source becomes infinity.

If that is possible, then \$V_2 = -\infty\$


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.