[sdiy] more LM3900 stuff

[JH.]

I've been reading up a little history.
So, as I understand it:

The LM3900 was the first quad opamp.

The driving force for 4 pamps in one package was the automotive industry.

There wasn't enough space for an input diff pair on the die, so they
invented
a new type of opamp that worked with currents, going into what
normally would be the second stage.

Then the LM324 was the first quad to feature a split collector diff pair
input stage - gm reduction which allowed small compensation capacitors.

(paraphrasing from Fredriksen, "Intuitive IC Op Amps", 1984)

As for the "strange" pinout, the LM3900 _could_ have defined the pinout
of quads forever, if it wasn't for the LM324 that had a different pinout,
but was much more a "real" opamp.

JH.