Problem with continuous cmfb circuit from Gray's textbook

hi
i designed a continuous cmfb circuit as was showed in the attachment
but it does now work as i expected
its output is 1.56V at the typical corner
when i changed everything (any or the transistors) of the cmfb circuit
and the ota transistors
the output does not change
also it oscillates when at the fast corner
and the slow corner
the circuit and the simulation result ,and test circuit are showed in the attachments
the cmfb circuit was copied from Gray's text book
could anybody tell me where is problem?
thanks
thank u very much.
best regard

Re: question about cmfb~

Hi.

frankwen said:

but it does now work as i expected

Click to expand...

Both inputs of CMFB are connected to the negative output (vout-). Also n-wells of PM25, PM26, PM27 aren't connected to vdd.

frankwen said:

also it oscillates when at the fast corner
and the slow corner

Click to expand...

To increase stability of the CMFB loop try to split transistor PM27 into two parallel transistors: one with fixed bias, other with gate connected to CMFB output.

Re: question about cmfb~

thank you very much for your reply
i'll try
thank again
best regards

dedalus said:

Hi.

frankwen said:

but it does now work as i expected

Click to expand...

Both inputs of CMFB are connected to the negative output (vout-). Also n-wells of PM25, PM26, PM27 aren't connected to vdd.

frankwen said:

also it oscillates when at the fast corner
and the slow corner

Click to expand...

To increase stability of the CMFB loop try to split transistor PM27 into two parallel transistors: one with fixed bias, other with gate connected to CMFB output.

Click to expand...