yvkrishna
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Hi,
This is a famous classAB opamp topology, It uses translinear principle to bias the transistors Q10,Q11.
Vb1,vb3 are the voltages to bias the cascode transistors Vb3 = vov_Q1c + vth_Q1c + vov_Q5
vb1 = Vdd - ( vov_Q3c + vth_Q3c + vov_Q3)
Vb5,vb6 will be clear to understand if you draw the complete bias circuit.
you can refer chapter12 of Analog Design Essentials by Willy Sansen
Regards, yvkrishna
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