(a) Show that as long as Cgd ! Cgs, the smallsignal impedance Zd seen looking into the drain of the FET of Fig. P6.15 can be modeled with the network shown at the right. What are the expressions for...

(a) Show that as long as Cgd ! Cgs, the smallsignal impedance Zd seen looking into the drain of the FET of Fig. P6.15 can be modeled with the 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 Cgd ! Cgs to simplify your calculations. (b) Calculate Rx, Cx, and Cy if the FET has gm 5 2.0 mA/V, ro 5 50 kV, Cgs 5 100 fF, Cgd 5 10 fF, Cdb 5 20 fF, and the input source has Rsig 5 10 kV. (c) Sketch and label the frequency plot of uZd(jf)u from 1 MHz to 10 GHz (use logarithmic scales). Hint: fi rst plot the impedance uZxu 5 uRx 1 1ysCxu. 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.