Dear Wjxcom,
If you know which transistor is in cut-off region, do you can't analysis its reason?
Just analyze its current and voltage.
It is complex to see your circuit, would you please attach it in PDF format?
Good luck
Regards,
Philip
wjxcom said:
Hi all: may be nobody know the reason? this circuit can be found in the paper "A Compact Power-Efficient 3 V CMOS Rail-to-Rail Input/Output Operational Amplifier for VLSI Cell Libraries" and I modify the circuit to full differential OPA, as shown in the attachment!
Help me please, thanx!!