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1 + ju/o>a n , //-. „ 1 + j<o(l/<Qa + a(,T)/( 1 - fflp)

Fig. 2-21 Circuit for finding the high-frequency value of hm and /121&.

From the last equation hub can be shown to be the impedance Ze in series with an RL parallel circuit, as shown in Fig. 2-22. Note that the impedance Au& (and the actual input impedance if the load impedance in the collector is small) is inductive over a considerable frequency range; that is, | An & | increases with frequency from approximately

The quantities h22b and A12ft may be obtained by inspection from Fig.

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