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Bob Pease and opamp-modelling

I came across the following article by analog guru Bob Pease concerning real opamp behaviour:

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Unfortunately the article is printed/edited badly, which makes it hard to understand what Bob is trying to tell e.g the first formula should be: AV =3D AV_O =D7 1/(1 + s =D7 tau_ol) or AV =3D AV_O =D7 1/(1+ s/( 2piF_O))

for the second formula I guess p is equal to pi and the question mark should be an integral sign in the third formula he uses p first as the differential operator and then as pi

I can't however figure out what he means with the fourth formula? Can anyone here explain what Bob means (clarify the symbols he uses there)

regards, Candide Voltaire

Reply to
Candide Voltaire
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I can't make out what he means from the rendering of the article - makes no sense to me either.

There is a simple way around his dislike of using the -3dB point of the Laplacian open-loop gain expression:

H=3D Ao ----------------- 1 + (s*Ao/wo)

where Ao is the dc open loop gain, and the new wo is the radian frequency at which the gain goes to unity. While it is a tiny bit ugly (Ao appearing twice), it can now be varied without altering wo.

-f

Reply to
cassiope

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As usual, Pease tries to make things too complicated.

The "AC" gain is simply GBW/s, where s is the Laplace variable.

DC gain is just a straight _horizontal_ line, of value, Gdc.

The "corner" is the intersection of Gdc and GBW/s.

See the behavioral OpAmp model on my website for more details.

...Jim Thompson

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| James E.Thompson, P.E.                           |    mens     |
| Analog Innovations, Inc.                         |     et      |
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Reply to
Jim Thompson

Thanks for answering but I think the expression you suggested should be: A0 H=3D----------------- 1+ s /w0

with A0 the DC-gain and w0 the openloop corner frequency (rad/ s) of course Bob's equation (4) still remains a mystery

Reply to
Candide Voltaire

maybe he does, but to be sure of that we first have to know what he really meant with the fourth equation... I guess we all know here the first order opamp model but Bob seems to want to replace it with a more accurate model, I really like to know what it is, I don't care if it is in the time domain or in the f-domain as converting from one to the other is not difficult.

Reply to
Candide Voltaire

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