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Op Amp model

Hi,

I want to model an Op Amp using a laplace transform. How can I do this if there is a single pole and unity gain frequency of 2.31Mhz?

What would be the H(s) equation?

Any help is greatly appreciated,

Michael

Reply to
michael.mcgarry
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What grade will I get from the instructor ?:-)

...Jim Thompson

-- | James E.Thompson, P.E. | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona Voice:(480)460-2350 | | | E-mail Address at Website Fax:(480)460-2142 | Brass Rat | |

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| 1962 | I love to cook with wine. Sometimes I even put it in the food.

Reply to
Jim Thompson

Indeed. It's the unity-gain frequency s2 = K/T that opamp designers try to keep stable, not the DC gain K. If Michael substitutes K/s2 for T, so the single opamp pole s1 = s2/K, he'll have an opamp model that's independant of K, to first order, just as in the real world. Then H(s) ~= K / (1 + s K/s2) = 1 / (1/K + s/s2), where s2 is the unity-gain frequency, and the actual DC gain K doesn't matter much.

--
 Thanks,
    - Win
Reply to
Winfield Hill

I prefer re-arraigning,

H(s) = 1 / (s/GBW + 1/GDC) ~= 1 / s/GBW = GBW/s

In this it's clear we can usually ignore 1/GDC ~= 0, yielding H(s) = BGW/s - which is useful because it highlights an important opamp parameter.

--
 Thanks,
    - Win
Reply to
Winfield Hill

GDC = DC Gain

GBW = Gain-Bandwidth in radians/sec

H(s) = (GDC*GBW)/(GDC*s + GBW)

or

H(s) = GBW/(s + GBW/GDC)

...Jim Thompson

-- | James E.Thompson, P.E. | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona Voice:(480)460-2350 | | | E-mail Address at Website Fax:(480)460-2142 | Brass Rat | |

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| 1962 | I love to cook with wine. Sometimes I even put it in the food.

Reply to
Jim Thompson

Plain zero :-) Your model will have additional lag and won't reach the instructor's desk in time.

--
Thanks,
Fred.
Reply to
Fred Bartoli

It's K/(1+ST) where you need to find K and T. You can find its magnitude and equate to unity then substitute 2.31MHz freq. ie s=j omega = j*2*pi*2.31e6. It appears that K and T may not be unique.

McC

Reply to
Real_McCoy

"re-arraigning"??? I didn't know you were a prosecutor. I'll have to introduce you to one of my sons-in-law ;-)

...Jim Thompson

--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC\'s and Discrete Systems  |    manus    |
|  Phoenix, Arizona            Voice:(480)460-2350  |             |
|  E-mail Address at Website     Fax:(480)460-2142  |  Brass Rat  |
|       http://www.analog-innovations.com           |    1962     |
             
I love to cook with wine.      Sometimes I even put it in the food.
Reply to
Jim Thompson

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