(a) Show that the impedance Zb seen looking into the base of the BJT of Fig. P6.20 can be modeled with the network shown at the right. Hint: apply the test method to the high-frequency equivalent of...

(a) Show that the impedance Zb seen looking into the base of the BJT of Fig. P6.20 can be modeled with the network shown at the right. Hint: apply the test method to the high-frequency equivalent of the circuit shown at the left, and express Zb as Zb 5 rb 1 [Rx//(1ysCx)] 1 (RE//ro). Do this fi rst with C 5 0, and then add C to your circuit at the end. What are the expressions for Rx and Cx? (b) Calculate all element values using the data of the emitter follower of Example 6.11.