thru zero VCO questions (4th attempt)

[Rene Schmitz]

Hi all, 

my previous attempt to write this didn't seem to come through so here I go
again.

I wan't to develop a thru zero capable VCO, and I have some questions
regarding it. I can see from "prior art" that one uses integrators that can
go up and down, depending on the polarity of the FM input signal. In the
ones I've seen the FM input is rectified, fed into the reference input of
the expo convertor, and the whole oscillator is switched between forward
and backward. Why is it done that way? I think all one would have to do is
to replace the schmitt-trigger with a window comparator which toggles a
D-flipflop between forward and backward when the thresholds of the
comparators are met. The output of the flipflop would be switching the
polaritiy of the FM input sum. Or am I missing something here? 
My brain already hurts, so any comments highly welcome.

Bye
 René  

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