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[Moved]: calculating 3db freq/ UGB from closed loop gain, open loop gain

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bharat_tangudu

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Hai,

It may be a silly question all of you. But, I don't know the answer.

How can I find the 3db frequency of op-amp if only open loop gain and closed loop gains are given?

pl someone respond.
 

Re: calculating 3db freq/ UGB from closed loop gain, open loop gain

The question is not "silly" - but incomplete.
What means "given"? As a formula or as a drawing? Or with DC gain and pole/zero positions?
 

Re: calculating 3db freq/ UGB from closed loop gain, open loop gain

i was given the values of open loop gain and closed loop gain and i was asked to calculate the 3db frequency of opamp.

i want to know is there anyway to find out this value through formula or drawing or any other way

i felt like data given was incomplete
 

Re: calculating 3db freq/ UGB from closed loop gain, open loop gain

i was given the values of open loop gain and closed loop gain
Click to expand...
Doesn't answer the question by LvW. What do you mean with "values"?
 

Re: calculating 3db freq/ UGB from closed loop gain, open loop gain

Hi,

If UGB is 1MHz
And closed loop gain is 20

Then you may estimate about 1MHz / 20 = 50kHz closed loop bandwidth.
If you need to take -3dB into account then maybe is 50kHz x 1.41 = 70.7kHz.
But this is a raw estimation, because UGB is a raw estimation, too. It varies with production.

I don't know if this is what you need to know.

Klaus
 

Re: calculating 3db freq/ UGB from closed loop gain, open loop gain

FvM said:
Doesn't answer the question by LvW. What do you mean with "values"?
Click to expand...

values means...

open loop gain of opamp is 70db. if the same opamp used in noninverting configuration which provides gain of 50 in linear, then what would be 3db frequency of opamp?

this is the question i was asked as it is...

apart from this data, no other data was given to me
 

Re: calculating 3db freq/ UGB from closed loop gain, open loop gain

The opamp i am trying to mention is two stage opamp
 

open loop gain of opamp is 70db. if the same opamp used in noninverting configuration which provides gain of 50 in linear, then what would be 3db frequency of opamp?
Click to expand...
Incomplete information. Either OP poles/zeros or GBW for a first order estimation must be known.
 

Thanks for the reply and i have been given GBW to calculate 3db frequency
 

Hi,

So you say:
open loop gain is 70dB, closed loop gain is 50. GBW is a secret (at least for us).

So we can just refer you to post#5.

Klaus
 

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