(a) Show that as long as C ! C, the small-signal impedance Zc seen looking into the collector of the BJT of Fig. P6.12 can be modeled with the all-passive network shown at the right. What are the...

(a) Show that as long as C ! C, the small-signal impedance Zc seen looking into the collector of the BJT of Fig. P6.12 can be modeled with the all-passive network shown at the right. What are the expressions for Rx, Cx, and Cy? Hint: apply the test method to the highfrequency equivalent of the circuit at the left, and exploit the condition C ! C to simplify your calculations. (b) Calculate Rx, Cx, and Cy if the BJT has gm 5 1y(40 V), 0 5 150, ro 5 100 kV, rb 5 300 V, fT 5 400 MHz, C 5 0.45 pF, Cs 5 0.55 pF, and the input source has Rsig 5 2.0 kV. (c) Sketch and label the frequency plot of uZc(jf)u from 1 kHz to 10 GHz (use logarithmic scales). Hint: fi rst sketch and label the plot of the series combination of uZx(jf)u, where Zx 5 Rx 1 1ysCx. Next, use physical insight to assess the effect of adding ro in parallel. Finally, use again physical insight to assess the effect of adding Cy.