integrators or followers

[Magnus Danielson]

From: "Tony Allgood" <oakley at techrepairs.freeserve.co.uk>
Subject: integrators or followers
Date: Fri, 4 Feb 2000 20:30:11 -0000

> Hi there,
> 
> Looking at designs using OTA integrators, like SVFs and VCOs. I notice
> that some have the cap bolted to the OTA output and ground, and the
> signal is then buffered by a follower of some sort. While some have the
> cap around an op-amp integrator. Any advantage in doing it this way?

The only real benefits I can see is that the OTA output operate towards a fixed
voltage level (the virtual ground) which may be beneficial for their output
stage. As I recall it some OTAs will get degraded preformance as you move the
operating point of the current output so a current follower is needed and
recommended. But instead of using a resistor you just stuff your cap in and
you got your integration operation as you wished to have it.

Another fully valid reason is that this is the cheapest way of getting
an inversion since you anyhow must buffer the output of the capacitor, so the
op-amp must be there anyhow, so just setting it up diffrently makes it do the
inversion for free.

I'd love to hear about more reasons thougth.

Cheers,
Magnus