[sdiy] Very fast VCO!

[René Schmitz]

Hi Karl and all,

karl dalen wrote:
> I just have made a sawtooth core that oscillates between 2hz and
> about 5Mhz using a 80Mhz comparator, is it a bad idea to assume good
> linearity with saw cores at these frequencies? Would i be better out
> doing these with triangle core instead?

Discharge time should scale with cap size, i.e. it would decrease as you 
go up in frequency. What you need to watch out in RF land is parasitics, 
Ls and Cs which make tuned circuits that lead to overshoot, ringing and 
so on.

> Triangle cores would have better over all linearity then sawtooth's,
> however it would be nice to use the saw since there are very few
> components involved!
> 
> I have it oscillating on the breadboard and stray capacitances soften
> up stuff but otherwhise it looks neat.

Well, I'd divide it down, and see if the precision is good enough. Maybe 
you can get away with simple reset time or Rbe (over)compensation.

Cheers,
  René

-- 
uzs159 at uni-bonn.de
http://www.uni-bonn.de/~uzs159