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Fully differential Opamp CMFB - Strange behavior in closed loop

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Hi All,
I'm still on TT polyphase filter with current input and I saw a strange behavior in this structure when I'd simulated the CP1.

My Opamp is a classical 2 stages with a CMFB on activ load. In Open loop the gain is 58dB for a UGF at 27MHz and Phase margin is 45 degree.

The stange behavior is the following:
In the global strucure, when I'm applying a current sine on I and Q ways, the voltage point generated on Iinp and Iinn are not on opposite phase, they are in pahse Oo' !!!
When I add a vcvs with unity gain on each outp (outp and outn), the signals I and Q are in opposite phase.
What could be the issue ?
Thanks in advance for your help.
 

Hi,
This behavior sounds like you have more than one DC valid OP. If you are running an AC simulation try setting initial conditions. Or you should run transient with a ramp up on your voltage supplies and check the OP. If you do have an extra state valid for DC OP you should add a start circuit.
 

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