[sdiy] VCO reference voltages

[Magnus Danielson]

David G. Dixon wrote:
> Does anyone here have any strong views on deriving reference voltages from
> the power supply rails in VCOs for comparator or schmitt trigger thresholds,
> etc (as opposed to using precision references)?  I know that most "DIY" VCO
> designs do so.  I'm wondering whether most commercial VCOs also do so, and
> whether it is considered "kosher", even in more expensive VCOs.

There is a hidden cancellation in there. The comparator voltage and the 
current reference voltage actually cancels themselves. You want to 
maintain that property.

AC modulations will not cancel like that.

Cheers,
Magnus