[sdiy] Re: linear FM

[ASSI]

On Wednesday 05 February 2003 22:07, Magnus Danielson wrote:
[...triangle relaxation oscillator...]
> That's only one way of viewing it. However, there is actually a
> contra-proof to this, if you look carefull you will find the rising
> time being a little different from the falling time. 

That's a deficiency of the implementation, with best regards from real 
life. :-)

My point was (and as I announced at the beginning of my original 
posting I hadn't spent enough time polishing it) that you can view an 
ideal triangle relaxation oscillator as a very special case of a 
linear-through-zero VCO, with it's frequency centered at zero and being 
modulated by a perfect square wave, the amplitude of which determines 
the frequency of the resulting wave.

All that state-machine stuff and talk about trigger thresholds assumes 
a very different (and equally valid) view of that oscillator that has 
some very nice properties that make implementation easy. But as you 
also observed, the details of that implementation run counter to 
obtaining the desired linear-through-zero operation. Simplistically 
speaking, that is because you already use the "frequency modulation 
input" for the normal operation of the oscillator. Your addition of the 
Gilbert cell already recognizes the need for mixing the two 
modulations, however in the actual implementation you can't get at the 
actual square which means you can't properly mix it with the FM input 
that you intend to have additionally available.

I hope that clears up what I was trying to get at, otherwise I better 
stop the discussion.


Achim.
-- +<[ Q+ & WAVE#46 & microQkb Omega sonic heaven ]>+ --

ForumThree Q and microQ Soundset:
http://homepages.compuserve.de/Stromeko/ForumThree_Q.zip
http://homepages.compuserve.de/Stromeko/ForumThree_uQ.zip