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How does one determine value of capacitor to be used with LM108 pins 1 and 8

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matrixofdynamism

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The datasheet of TI LM108 shows pins 1 and 8 as "Comp". I take this to mean compensation. The datasheet shows that for a capacitor of capacitance Cf connected here, the "Bandwidth and slew rate are proportional 1/Cf". But, how does one know what value capacitor to use and should the capacitor be connected between pins 1 and 8 or pin 1 and ground?
 

Why don't you use the minimal Cf value according to the datasheet formula?
 

The LM108 is very old, is obsolete and is not made or available anymore. When it was designed they did not know how to fit a compensation capacitor inside it like all modern opamps have.
 

LM108 was designed by Bo Widlar one year after Fairchild released uA741. LM108 has new features that were not available with other OPs before, particularly the < 1 nA input compensation. The external compensation is a feature in some regards because it allows to make decompensated amplifiers with higher GBW product than universal compensated types.

And yes it's obsolete now, although it has been produced in lead-free technology for some years. You can get still get LM108 exemplars at some catalog distributors.
 

I see. So the internally compensated superior versions have taken its place.
 

With almost no capacitance, an old LM108 cannot even produce the highest audio frequency of 20kHz at full output but a modern TL071 audio opamp produces frequencies to 100kHz perfectly without adding anything.
 

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