# Open Loop Gain

#### xn47

Joined May 22, 2007
22
Do you have any easier approach on how to solve the open loop gain of OP-AMP (741 in particular)?

#### Dave

Joined Nov 17, 2003
6,970
An easier approach than what method?

Dave

#### beenthere

Joined Apr 20, 2004
15,819
The spec sheet on the device gives the open loop gain. Let the fab house do the work.

#### bloguetronica

Joined Apr 27, 2007
1,372
Perhaps, negative feedback. Hence we have a closed loop gain, substancially smaller than the open loop gain (since open loop gain is the gain of the op-amp as it is).

But I'm in the dark here, since I'm not sure if you want to decrease gain (what do you mean by "solving the open loop gain"?).

#### xn47

Joined May 22, 2007
22
An easier approach than what method?

Dave
than small signal analysis

#### Ron H

Joined Apr 14, 2005
7,014
Do you want to measure open loop gain with test equipment?

#### xn47

Joined May 22, 2007
22
by computation. Actually I have finished discussing that topic with my group. Right now, I am currently hooked in computing common mode gain of differential amp using bisection theorem. where; Acm = (-gmRc)/[(1+2gm.REE)(1+1/Beta)]

hmm.. hows that? If its not too much to ask..

#### xn47

Joined May 22, 2007
22
I have here an attachment of half ckt wherein I transform its current source to its Norton equivalent ckt.. where REE is shunted to the source. How will you get Common mode gain as I state in my last reply..
Thanks..

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#### Ron H

Joined Apr 14, 2005
7,014
I'm not sure that's relevant to a 741. It does not take the output off one collector. It has a current mirror on the output of the differential input stage. The common mode gain is really only a function of how well balanced the current mirror is.

#### xn47

Joined May 22, 2007
22
Thanks.. this is another case..

#### Distort10n

Joined Dec 25, 2006
429
Although I am not sure, I would imagine manufacturers use a Venable and sweep across the frequency spectrum to measure open loop gain. The result would be the Bode plot in the datasheet.
I have no idea what the test set up would be.