Introduction to Electric Circuits

208 Two-port networks

9.3 THE ADMITTANCE OR y-PARAMETERS

Set 2: If V~ and V2 are the independent variables then the dependent variables
are given by:

11 - y11V1 + y12V2 (9.8)

I2 = yz1V~ + yzzV2 (9.9)

In matrix form

[,11: ry11 y12] iv11
I2 LY21 Y22J V2

The parameters for this set are called the admittance or y-parameters and they
are defined as follows:

9 Yll is the input admittance (Yi) and is measured as I1/V 1 with V2 = 0:

Yll = (I1/V1)[v2=o (9.11)

9 Y12 is the reverse transfer admittance (Yr) and is measured as I1/V 2 with

V1 = O:

Y12-- (I1/V2)[Vl=O (9.12)

9 Y21 is the forward transfer admittance (yf) and is measured as I2/V~ with

V2 = 0:

y~, = (I~/Vl)lV~=o

9 Y22 is the output admittance (Yo) and is measured as I2/V2 with V1 = 0:

(9.13)

Y22 = (I2/V2)lv,=o (9.14)

Since these are obtained with the output or the input port short circuited, they

are called the short circuit admittance parameters and are measured in siemens.

They are commonly used in the analysis of field effect transistor (FET)

circuits.

The equivalent circuit for this set which satisfies Equations (9.8) and (9.9) is

given in Fig. 9.4.

+O

V1

--O

Yll y12V2

1

Y21V1 I

1

I2

Y22 V2

O--

Figure 9.4