Electrical Engineering ⇒ Topic : ABCD-parameters

ABCD-PARAMETERS

The input voltage and input currrent are expressed in terms of output voltage and output current in ABCD-parameters. For a two-port network Figure (1), it can be written as:

                                   V₁ = Z₁₁I₁ + Z₁₂I                                 ..............(1)

                                   V1 = AV₂ - BI₂                                    ..........(2)

                                    I₁ = CV₂ - DI₂                           ...........(3)

In matrix form, it can be obtained as:

                                  .............(4)

It is conventional to call the input port as sending-end while the output port as receiving end. In Eq. (4), the negative sign due to the reference direction of I₂ which is opposite to that in power transmission problems

                             Assuming I₂ = O, i.e., the output port to be open-circuited. Mathematically

                                                             ............... (5)

                                                              ............... (6)

Assuming V₂ = 0, i.e., output port to be short-circuited, it can be written as:

                                                             ................... (7)

                                                             .................... (8)

A is called reverse voltage ratio and it has no unit. C is known as transfer admittance and its unit is mho (or siemens). D is called reverse current ratio and it has no unit. B is known as transfer impedance and its unit is ohm.