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

[Magnus Danielson]

From: "Czech Martin" <Martin.Czech at Micronas.com>
Subject: linear FM : was RE: [sdiy] Temperature Compensated VCO attempt - help?
Date: Tue, 4 Feb 2003 10:04:39 +0100

> I may miss the point here but I think the real
> problem is in the storage element that decides charge up/down
> direction. 
> 
> If this is the case, read on.
> If not, complain.
> 
> Obviously there are situations where
> the comparators want up and the sign "toggler" wants
> down or vice versa. This can also lead to meta stability
> problems since the timing of up/down and toggle
> is unknown.

Actually, what I said was than when you reach EITHER of the two limits you
want to swap the direction, regardless of which limit and which direction you
currently have in your "storage element" or "state machine".

You are correct that there is an issue with meta stability. You always have
this issue creaping up on you.

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.

But I don't know... it seems everyone else know this far better than me and I
can't contribute anything... and when one does share a what seemed like a good
idea people kill it :(

Magnus