12.36 Figure P12.36 shows a variant of the class AB circuit of Fig. 12.16. Assume that all four transistors are matched with β = 100 except that the emitter area of Q3,4 is 10 times that of Q1,2.
(a) For vI = 0, find the quiescent current in Q3 and Q4, the input current iI, and the output voltage vO.
(b) Since the circuit has perfect symmetry, the small-signal performance around vI = 0 can be determined by considering either the top or bottom half of the circuit only. In this case, the load on the half-circuit must be 2RL, the input resistance found is 2Rin, and the output resistance found is 2Rout. Using this approach, find Rin, vo/vi, and Rout (assuming that the circuit is fed with a zero-resistance source).