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and I 2 � � � �h o� E 2<br />

Thus,<br />

E 2<br />

hrh f<br />

�<br />

hi � Rs 1<br />

Zo ���—— I2<br />

hrh<br />

f<br />

ho � �� hi �<br />

(26.48)<br />

EXAMPLE 26.12 Determine Zi and Zo for the transistor having the<br />

parameters of Example 26.11 if Rs � 1 k�.<br />

Solution:<br />

Zi � hi � �1 k��<br />

� 1 � 10 3 � 0.0381 � 10 3 � 961.9 �<br />

Zo � �<br />

1<br />

1<br />

���� ����6<br />

25 � 10 15 � 10<br />

Zo � 66.67 k�<br />

�6 � 10 �10 �6<br />

1<br />

———<br />

25 mS �� (4 � 10<br />

1 k� �<br />

�<br />

hrh fZL 0.04 k�<br />

�� �<br />

1 � hoZL 1.050<br />

1<br />

——<br />

h<br />

4<br />

rh f<br />

)( 50)<br />

ho � �� �<br />

hi � Rs 1 k�<br />

E s<br />

R s<br />

+<br />

–<br />

For the z-parameter equivalent circuit of Fig. 26.53,<br />

I 1<br />

+<br />

E 1<br />

–<br />

Z i<br />

z 11<br />

+<br />

z12I2 –<br />

FIG. 26.53<br />

Determining Z i for the z-parameter equivalent network.<br />

and I 1 �<br />

z 21I 1<br />

I2 � ��<br />

z 22 � ZL E 1 � z 12I 2<br />

��<br />

z11<br />

R s<br />

+<br />

z21I1 –<br />

z 22<br />

I 2<br />

2<br />

+<br />

Zo E2 or E1 � z11I1 � z12I2 � z11I1 � z12�� z 21I1 �<br />

and Zi � � (26.49)<br />

E1<br />

z12z<br />

21<br />

� � z11 � �� I1 z 22<br />

� Z<br />

For the output impedance, E s � 0, and<br />

� z 22 � Z L<br />

L<br />

–<br />

2′<br />

Z L<br />

INPUT AND OUTPUT IMPEDANCES ⏐⏐⏐ 1179

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