Im trying to design a cascaded amplifier with 3 common emitter stages. As long as the input AC voltage is below about 20mV the amplification is fine, as you can see on AMP1. But the output of AMP2 is also maximum at 20mV and and goes much below zero. AMP3 is also maximum 20mV. The bias of each stage is at 773mV. How can I modify the bias of the second and third stage for higher input /output amplitude than 20mV?