The emitter follower uses local series-shunt feedback to achieve high input resistance and low output resistance. These characteristics can be improved further if we apply additional negative...

The emitter follower uses local series-shunt feedback to achieve high input resistance and low output resistance. These characteristics can be improved further if we apply additional negative feedback, in the manner depicted in Fig. P7.19. In this circuit, aptly known as super emitter follower, Q1 is the emitter follower proper, and Q2 provides additional feedback around Q1. (a) Assuming 01 5 02 5 0, ro1 5 ro1 5 ro, and r1 5 r2 5 `, use the series-shunt procedure to estimate Ri and Ro, and verify that the presence of Q2 raises Ri and lowers Ro by a factor of 0 3 roy(ro 1). (b) Assuming 0 5 100 and VA 5 50 V, calculate Ri and Ro, compare with the values they would have if Q1 were operating alone at 1 mA, and comment on your results.