opamp compensation in integrator application (was:Re: Descret OTA )

[terry michaels]

Message text written by INTERNET:jhaible at metronet.de
>
Does this mean that I wouldn't have to care about the compensation of the
opamp
if my desired overall response is that of an integrator ? I thought not,
but I'm on
thin ice here. Could you further explain this ?

JH.
<

Hi Juergen:

Yes, you have to care about the compensation of the opamp for an
integrator.  Textbooks say the opamp must be compensated for unity gain. 
This is contrary to what is in the ARP 4023, where the opamps are
de-compensated.  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.  The decompensation speeds up the LM301 by
9 times, and the two capacitors together ensure stability by attenuating
the feedback around the opamp.  As you pointed out in an earlier post, this
is the noise gain approach to stability.

Terry Michaels