The ABCD parameters for a 2-port network are:
V1 = AV2 −BI2 (28)
I1 = CV2 −DI2 (29)
Figure shown below shows a two-port network whose terminals RS are short-circuited with an input voltage V across terminals PQ. Then V2 in the above equations is 0 and the equations become:
V =−BI2 (31)
and I1 =−DI2 (32)
