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Design >> Analog Design >> Unity gain freq. and GBW
https://designers-guide.org/forum/YaBB.pl?num=1243268204

Message started by kidman on May 25^th, 2009, 9:16am

Title: Unity gain freq. and GBW
Post by kidman on May 25^th, 2009, 9:16am

What are the cases when fu isn't the same as GBW?

Title: Re: Unity gain freq. and GBW
Post by raja.cedt on May 25^th, 2009, 10:22am

hi,
why they should be equal?
if bode plot is falling with 20dB/dec then A1/A2=F2/F1 here A1 and A2 are the two different points on the plot and F!,F2 are corresponding frequencies. So now ugb=dc gain*3db.This is the only one case your claim work.

regards,
Rajasekhar.

Title: Re: Unity gain freq. and GBW
Post by thechopper on May 26^th, 2009, 5:04pm

Hi Kidman,

In short, fu=GBW only if the system is a first-order one. If the system is of higher order then fu ≈ GBW only if there is a dominant pole (i.e. second and higher poles are far away from it). When 2nd pole is < 5×GBW then the difference between fu and GBW is noticeable.

Hope this helps
Tosei