opamp compensation in integrator application

[Joachim Verghese]

> The LM 301 is faster than you think in this circuit, it is
> de-compensated by using a 3.3 PF cap.  That will produce a
> speed increase of 9 times.

Right. There's an unfortunate tendency to dismiss those old
op-amps as crap ("What? You haven't replaced yours with LF411s
yet?").

> Normally in a case like this, stability can only be guaranteed
> if the closed loop gain is at least 9, which is impossible for
> the usual type of integrator. However, this one has a 100 PF
> integration capacitor, and the inverting node of the opamp has
> a 1000 PF cap to ground. This attenuates the feedback by a
> factor of 11, which is sufficient for stability.  Now it makes
> sense.

Thanks for explaining that. And I just realised I need to review
the theory on amplifier feedback. :-)

BTW, when did VC integrators first appear in VCF designs?
Was ARP's Multimode filter the first?

-joachim