(a) Assuming Cgb, Cgd, Csb are negligible compared to Cgs, show that the input impedance Zi of the source follower of Fig. P6.26 can be modeled with RG in parallel with the series combination of a...

(a) Assuming Cgb, Cgd, Csb are negligible compared to Cgs, show that the input impedance Zi of the source follower of Fig. P6.26 can be modeled with RG in parallel with the series combination of a suitable capacitance Cx and resistance Rx, as shown. What are the expressions for Cx and Rx? (b) Find Cx and Rx if RG 5 100 kV and RS 5 2 kV, and the FET has k 5 4 mA/V2 , 5 0.05 V21 , 5 0.125, and Cgs 5 3 pF, and is biased at ID 5 2 mA. (c) Sketch and label the frequency plot of uZi (jf)u from 100 kHz to 10 GHz (use logarithmic scales). (d) Now consider the case Cgb5 50 fF, Cgd5 100 fF, and Csb 5 500 fF. To account for the presence of these capacitances, the model needs to be augmented with Cy and Cz , as shown. What does Cy model, and what is its value? What does Cz model, and what is its value? (e) Discuss how Cy and Cz affect the plot of part (c). Hint: fi nd Zi`.