Use Blackman€™s impedance formula to find the output resistance of the active-cascode current source in Fig. 8.55. Express the result in terms of g_m1, g_m2, r_o1, r_o2, and a, which is the voltage gain of the op amp. Assume all transistors are active with (W/L)₁= (W/L)₂= (W/L)₃and γ = 0. (The drain of M₂connects to other circuitry that is not shown.) Also, assume that the op amp has infinite input impedance and zero output impedance.

(a) Carry out the calculations with respect to controlled source g_m2.

(b) Repeat the calculations with respect to the voltage-controlled voltage source a in the amplifier.

(c) Compare the results of (a) and (b).

Fig. 8.55:

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VDD VBIAS M2 - Rout M1 Мз -Vss