cross-over distortion

output stage of an op-amp. when -0.6<v0<0.6v, vout = 0. cross-over distortion because  Vbe of Q1 and Q2 are too low to turn the transistors on.

By adding two diodes, we can increase Veb of Q1 and Q2 and  force them to turn on.

Increase current at current source will increase voltage across diodes. At I = 0.1mA, we see the distortion is reduced.

At I = 2mA, voltage across diodes are high enough to turn Q1, Q2 fully on. Distortion eliminated.

Alternertively we can replace diodes with transistors, same principle.

When I = 0, distortion.

when I = 10uA, distortion reduced.

When I = 40uA, distortion eliminated.

Input 1mV sin wave.

When I = 0, working within distortion range of input, output is unresponsive. (few uV).

When I = 40uA, get rid of distortion, output is significant. (400mV).