fully differential folded cascode

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B Swapna

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Hello
I am new to this forum, hope someone could help me
i am designing a fully differential folded cascode opamp with gain boosting technique for pipeline adc.
i have used pmos input stage, so what would be the input stage of gain boost opamp. does the gain boost opamp can be a simple opamp, or it should also be a folded cascode. also i have used CMFB circuit, so what should be the current flowing in this circuit.
thanku
swapna
 

The boost amp can be a one-stage amplifier. You can refer to the book of pr gray, in which, there's detail.
 

The additional gain stage (gain boost amplifier) can be any "amplifier", of couse it can be folded cascode, it even can be just a single MOS together with a current source.
If the additional gain stage is also implemented by cascode topology, the gain enhancement techniques can be repetitively used to further boost the gain. The limitation is set by factors such as leakage current, weak avalanche and thermal feedback.
 

I assume you need gain boosting on both the P-side and N-side output transistors. In those cases, you can use a signle simple stage OTA with PMOS input pair and NMOS input pairs. What extra gain you need basically determines the topology of these gain boost amps. There should be plenty of literature covering these stories.
 

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