Op Amp model

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 | |

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.

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.

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 | |

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

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

"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