I have implemented this circuit(I mean Class-AB outout stage and summing circuit).
M19 and M20,the mesh transistors,compose a "floating voltage source".
Voltage difference between M19's source and M20's source is 1.137V in my circuit and quiescent currents flow through M19 and M20 are 7.5uA.
But, when a small voltage signal is applied on gates of complementary input transistors, there is still voltage sine vibration between M19's source and M20's source,and magnitude is about 1mV.
If anyone knows something about this circuit,PLZ tell me.I appriate the help.