ODP: thru zero VCO questions

[Roman Sowa]

1. whatever will be starting position of FF, VCO's integrator will
travel from 0V (hopefully) to one of thresholds. When it reaches
any of them, FF toggles, and integrator changes direction.
I see no problem here. Noise and metastability - those are
the problems we're trying to solve. Maybe using 2 sets of
comparators, and pulse "spray" can fix it completely.

2. AFAIK FM input will be used only for modulation, so stability
or distortion isn't such a problem. I don't have objections using
OTA input for FM. Done that in my quadVCO, where it is set
to a certain voltage, and modulated from FM input. Works fine.
I can even get through-zero FM, but very limited.

Roman

-----Oryginalna wiadomooeæ-----
Od: Martin Czech [mailto:martin.czech at intermetall.de]
Wys³ano: 10 wrzeoenia 1999 10:32
Do: uzs159 at uni-bonn.de
DW: synth-diy at mailhost.bpa.nl
Temat: Re: ODP: thru zero VCO questions


I've got two objections:

-I can not see how the oscillation will be stable, the toggle ff could
be in the wrong state right from the start, or get into a wrong state
later on due to noise or metastability. Then the direction switch will
not work any longer, since the cap is integrated near to one power rail
and get stuck there.

-I can not see what advantage it should have using the nonlinear
OTA input for more then a polarity digital signal. The linear fm signal
will be distorted or drown in noise, and using the diff. input in "linear"
mode will cause offset problems, too.

m.c.