Open Loop Gain

Discussion in 'General Electronics Chat' started by xn47, Jun 13, 2007.

1. xn47 Thread Starter Member

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

2. Dave Retired Moderator

Nov 17, 2003
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An easier approach than what method?

Dave

3. beenthere Retired Moderator

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

4. cumesoftware Senior Member

Apr 27, 2007
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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"?).

5. xn47 Thread Starter Member

May 22, 2007
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than small signal analysis

6. Ron H AAC Fanatic!

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

7. xn47 Thread Starter Member

May 22, 2007
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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..

8. xn47 Thread Starter Member

May 22, 2007
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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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9. Ron H AAC Fanatic!

Apr 14, 2005
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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.

10. xn47 Thread Starter Member

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

11. Distort10n Active Member

Dec 25, 2006
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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.