Odp: linear FM : was RE: [sdiy] Temperature Compensated VCO attempt - help?

[Roman Sowa]

Back then I also had an idea, that even worked on breadboard.
It was saw thru-zero VCO. Basically it's well-known saw VCO
with integrator, comparator and clamping transistor. What I added
was second comparator, biased slightly below 0V. This comparator
drives a transistor, that immediately charges integrating capacitor,
but just below the point where 'normal' comparator triggers.
It was really simple, and if I find a schematic, I'll post it.

Roman
(responding a little late)

----- Original Message -----
From: René Schmitz <uzs159 at uni-bonn.de>
To: Magnus Danielson <cfmd at swipnet.se>; <Martin.Czech at Micronas.com>
Cc: <don at till.com>; <sbernardi at attbi.com>; <synth-diy at dropmix.xs4all.nl>
Sent: Tuesday, February 04, 2003 9:41 PM
Subject: Re: linear FM : was RE: [sdiy] Temperature Compensated VCO attempt -
help?


> I once proposed a circuit which does this. There should be quite a bit about
it
> in the archives because we did discuss here this back then. It was in '99. The
> subject was "thru zero VCO schematic".
> However the issues with forbidden states or metastability weren't resolved, so
I
> ended up with the design which is at my page. Which is saving the
rectification
> of the modulation signal, compared to the EN design, but still has a nonsteady
> transition because the sign of the FM input must still be sensed.
>
> >One way of solving the issue is to have the linear FM bandwidth limited (to
> >say 20kHz or something) and toss in a slight hysteresis for the upper and
lower
> >limit comparators, enought to ensure you get long enought pulses. Then you
> >should basically be home free.
>
> The problem lies in the nondeterminism: What do you do if the FM signal
changes
> its sign during that pulse?
>
> Cheers,
>  René
>
>
> --
> uzs159 at uni-bonn.de
> http://www.uni-bonn.de/~uzs159
>
>
>
>