quasi-complementary circuit, as shown in Fig. 12.18 . The push–pull operation is achieved by using complementary transistors ( Q 1 and Q 2 ) before the matched npn output transistors ( Q 3 and Q 4 ). Notice that transistors Q 1 and Q 3 form a Darlington connection that provides output from a low-impedance emitter-follower. The connection of transistors Q 2 and Q 4 forms a feedback pair, which similarly provides a low-impedance drive to the load. Resistor