[Moved] Common mode feedback circuit with 1 supply voltage

[han sang jun]

Currently. i am designing a folded cascode amplifier. i try to configure the feedback circuit using the DDA(Differential Difference Amplifier) CMFB circuit by settling vdd to 1v and output common mode to 0.5V . I don't think this is possible because of the threshold voltage. what do you think about my opinion?

 

[arthorios]

I don't think this is possible because of the threshold voltage. what do you think about my opinion?

That depends on how you are designing your folded-cascode and CMFB.
What is the VTH of the devices you are using? What is the output swing of the OTA?

 

[han sang jun]

I am planning to design it like this picture. so i want to get Av=500V/V Unit_G=50Mhz about folded cascode amplifier. so i think V dsat (current source in common mode feedbackback) is too large.

 

[frankrose]

If you apply floating/hot pwell bulk connection or native or LVT NMOS it can work I think.

 

[arthorios]

I am planning to design it like this picture. so i want to get Av=500V/V Unit_G=50Mhz about folded cascode amplifier. so i think V dsat (current source in common mode feedbackback) is too large.

To avoid the increase in VTH due to body effect you can go with a PMOS input cmfb and control the lower current sources instead. But it might still be the case that the swing is too large for this topology. A buffered resistive cmfb detector could solve it.