OTA VCF theory help

[Magnus Danielson]

From: Harry Bissell <harrybissell at prodigy.net>
Subject: Re: OTA VCF theory help
Date: Fri, 14 Apr 2000 00:24:02 -0400

> > Hello,
> > I have been looking at the ASM-1 state-variable filter and I have a few
> > questions.
> >
> > My main question is this: How does the filter design handle the fact that
> > the input signals are "large".  What I mean is, from what I understand
> > about the ota is that it only transconducts for a small differential
> > voltage range, outside that range the output current will saturate to the
> > max (or min) allowed by the Ibias current.
> >
> > I hope someone out there has some spare time to help me out with this!
> > (I also hope that my question makes sense)
> >
> > Thanks a bunch,
> > Hess
>
> not having the schematic in fromt of me, I'd say there is a huge resistive
> divider on each input... like 50-100K input and about 220 ohms or so to
> ground. Almost ALL OTA
> filters do this.

And so right you are, but the values are 10kohm over 22 ohm.

You should be able to see the resistor dividers easilly in the schematic.

Cheers,
Magnus