A crude BJT power amplifier of the class B (push-pull) type exhibits the VTC of Fig. P1.51b. The dead band occurring for −0.7 V ≤ v1 ≤ +0.7 V causes a crossover distortion at the output that can be reduced by preceding the power stage with a preamplifier stage and then using negative feedback to reduce the dead band. This is shown in Fig. P1.51a for the case of a difference preamplifier with gain a1 and b = 1 V/V. (a) Sketch and label the closed-loop VTC if a1 = 102 V/V. (b) Sketch vI , v1, and vO versus time if vI is a 100-Hz triangular wave with peak values of ±1 V.
