Introduction to Electric Circuits

212 Two-port networks

" g22 is the output impedance (go) and is measured in ohms as V2/12 with

V 1 : O:

g22- (V2/I2)lv,=o (9.28)

Note that

gll = 1/h~1 (9.29)

g21 = 1/h21 (9.30)

g12 = 1/h12 (9.31)

g22- 1/h22 (9.32)

For this reason the g-parameters are also known as the inverse h-parameters.

Equations (9.22) and (9.23) are satisfied by the equivalent circuit of Fig. 9.6.

Figure 9.6

+o I1

Vl

-o

gll

< I2 O

1

'-~ g22

g1212 l (~ V2

g21V1

o

Example 9.3

Determine the h- and g-parameters for the T-circuit of Fig. 9.3.

Solution

From Equation (9.18), hl1 = Vx/[1 with V2 = 0. Short circuiting the output port

terminals to make V2 = 0 places Z2 and Z3 in parallel and then

I~ : Vl/[Z 1 -~-{Z2Z3/(Z 2 -Jr- Z3)ll

Therefore

h,, - Viii 1 = Z 1 n t- {Z2Z3/(Z 2 Jr- Z3)}

Putting in the impedance values we have

hll = (10 + (5 x 5)/10) = 12.5 II

From Equation (9.29)

g~ = 1/hll = (1/12.5)S

From Equation (9.19), h21 = h/I1 with V2 = 0. By current division

6-- -II[Z3/(Z2 nt" Z3)]