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TWO-PORT NETWORKS

[CHAP. 13

13.15 The h-parameters of a two-port network are given. Show that the network may be modeled by the network in Fig. 13-26 where h11 is an impedance, h12 is a voltage gain, h21 is a current gain, and h22 is an admittance.

Fig. 13-26 Apply KVL around the input loop to get V1 ¼ h11 I1 þ h12 V2 Apply KCL at the output node to get I2 ¼ h21 I1 þ h22 V2 These results agree with the definition of h-parameters given in (23).

13.16 Find the h-parameters of the circuit in Fig. 13-25. By comparing the circuit in Fig. 13-25 with that in Fig. 13-26, we find h11 ¼ 4 ;

h12 ¼ 0;

h21 ¼ 0:4;

h22 ¼ 1=5 ¼ 0:2 1

13.17 Find the h-parameters of the circuit in Fig. 13-25 from its Z-parameters and compare with results of Problem 13.16. Refer to Problem 13.13 for the values of the Z-parameters and DZZ . Use Table 13-1 for the conversion of the Z-parameters to the h-parameters of the circuit. Thus, h11 ¼

DZZ 20 ¼4 ¼ 5 Z22

h12 ¼

Z12 ¼0 Z22

h21 ¼

Z21 2 ¼ 0:4 ¼ 5 Z22

h22 ¼

1 1 ¼ ¼ 0:2 Z22 5

The above results agree with the results of Problem 13.16.

13.18 The simplified model of a bipolar junction transistor for small signals is shown in the circuit of Fig. 13-27. Find its h-parameters.

Fig. 13-27 The terminal equations are V1 ¼ 0 and I2 ¼ I1 . By comparing these equations with (23), we conclude that h11 ¼ h12 ¼ h22 ¼ 0 and h21 ¼ .

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