4.50 In the capacitor-coupled attenuator circuit shown in Fig. P4.50, I is a dc current that varies from 0 mA to 1 mA, and C 1 and C 2 are large coupling capacitors. For very small input signals, so that the diodes can be represented by their small-signal resistances r d1 and r d2 , give the small-signal equivalent circuit and thus showthat v o v i = r d2 r d1 +r d2 and hence that v o v i =I, where I is in mA. Find v o /v i for I =0 μA, 1 μA, 10 μA, 100 μA, 500 μA, 600 μA, 900 μA, 990 μA, and 1 mA. Note that this is a signal attenuator whose transmission is linearly controlled by the dc current I.

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