Shown in Fig. P1.67 is an elegant currentcontrolled attenuator based on a pair of identical pn diodes operating in the small-signal mode. (a) Assuming C is large enough to act as an ac short, draw the...

Shown in Fig. P1.67 is an elegant currentcontrolled attenuator based on a pair of identical pn diodes operating in the small-signal mode. (a) Assuming C is large enough to act as an ac short, draw the equivalent small-signal circuit, and show that its gain is voyvI 5 IyIREF. (b) If IREF 5 1 mA, fi nd the current I needed for the following gains: 1 V/V, 0.75 V/V, 0.5 V/V, 0.25 V/V, and 0 V/V. What are the corresponding values of the equivalent resistance Req seen by the capacitor? (c) Specify a suitable value for C so that it acts as an ac short at 5 1 Mrad/s for all possible gain settings.