SC-CMFB for a folded cascode OTA - output is oscillating

[arunkumar446]

SC-CMFB

i have designed a SC-CMFB for a folded cascode OTA and when i check its transient response it's output is oscillating, can any one tell me why and how to avoid it, help me please it's urgent. Thank you in advance.

 

[arunkumar446]

Re: SC-CMFB

i found out from simulations that it's not because of instability but it is because of load variation, i.e., in two different phases there are two different equivalent cap's so two different feed back factors so the overall loop gain for common mode is varying so it looks like oscillating, if the SC-CMFB ckt capacitance is increased the overall CM gain will increase so difference between the oscillating peaks reduce.

 

[dineshbabumm]

SC-CMFB

It will initially oscillate but will eventually settle if I am right.. It takes certain cycles to settle and after that it will start functioning normally..

 

[arunkumar446]

Re: SC-CMFB

nope, it wont do that as it is going to change all the time but how much change can be tolerable is important in an application.

 

[mialee]

SC-CMFB

Hi
I'm new here
Could anyone please load this paper?


A Novel Method for Bandwidth and Phase Margin Enhancement of Folded-Cascode Amplifier
Publicación Analog Integrated Circuits and Signal Processing
Editor Springer Netherlands
ISSN 0925-1030 (Print) 1573-1979 (Online)
Fascículo/ejemplar/número Volume 46, Number 2 / febrero de 2006
DOI 10.1007/s10470-005-0652-z
Páginas 91-98

Thanks

 

[iamxo]

Re: SC-CMFB

U can use such type of sc-cmfb architecture which has equal load for both CM and DM loop.

 

[arunkumar446]

Re: SC-CMFB

ya right i have seen some architectures like dual phase sc-cmfb structures, we can use them only if we are ready to give more area.