Overshooting circuit ?

[Magnus Danielson]

From: Michael Buchstaller <buchi at takeonetech.de>
Subject: Overshooting circuit ?
Date: Wed, 29 Dec 1999 14:32:45 +0100

> Hello Group,
> 
> i have a simple question, but did not find an adequate solution for
> it, so i will ask the Gurus here ;-)
> 
> I know that Opamp designers do hell of a lot of work to make their
> devices as perfect as possible (low noise, fast etc.), and most modern
> Opamps do have internal circuitry to prevent overshooting.
> But i want a circuit that does exactly this. For example, when the input
> signal raises quickly ,say from 0 to 5 Volts (maybe a gate signal),
> i want the output voltage to go from the initially 0 V to 8V, then 3 V,
> then 7 V, then 4 V, then 6 V, then finally the 5 V. I do not know if my
> description is clear; i do want a damped oscillation, preferrably with
> VC damping.
> 
> My intention is to put a square wave from an LFO in the input, and
> hook the output to a VCO, so i expect to get sort of a 
> "Sproioioinnng..." sound.
> 
> Can anybody point me in the right direction ?

Ah!

What you want is a 2-pole lowpass filter, you can build this using a standard
op-amp, a few resistors and a pair of capacitors. If you want it tweakable
you would need more. Actually, what you want is just the same as our normal
"12 dB/oct lowpass filter" but operating at a lower frequency. I guess that
you would like to tweak the "height" of the Sproioioinnng as well as the
frequency of the oioioi part. The frequency relates to the frequency of the
filter - it's the same frequency. The "height" is related to the Q value
which will also relate to the decay time of the oioioi part. A higher Q will
get you higher peaking AND slower decay.

You should be able to mix the original signal and the filter output in order
to control the peaking separately from the decay parameter. This would make
your curcuit basically the same as a fully parametric equalizer.

You should be able to rescale many types off filters to acheive this. However,
in order to get the suitable control I would look at the state-variable type
of filters to start with.

I think the key to success lies in the ability to control the peaking heigth
relatively independent of the decay. I say relatively since there comes a
point where you have no peaking due to the filters Q value, so you can't make
it fully independent.

Actually, this seems to be a interesting little subject to ponder about.

Cheers,
Magnus