SV: Re: SV: [sdiy] More MOSFET saw VCOs

[karl dalen]

--- Ian Fritz <ijfritz at earthlink.net> skrev:

> At 06:22 PM 12/22/05, karl dalen wrote:
> >There is a parameter that says "gate capacitance changes
> >with frequency"!
> >
> >Do you se any differences regarding this parameter?
> 
> Hmmm ... interesting question.  Anyone know the answer?  :-)
> 
> There are other odd effects, too, like change in on resistance with 
> voltage. 

Yes, but thats a well known one!

 I suppose the gate capacitance mostly comes into play during the 
> discharge phase, which shouldn't depend on the VCO frequency.  But if there 
> is some feedthrough during the ramp ...

Most likely if it was a power mos,
the decay curve is very exponential.

I think the variation of Vgs is a problem, wheter this
is diffrenet between devices or the same for one entire batch
im not to shure but temp and voltage will do change it! 

> The waveform isn't perfect and changes a bit with frequency.  So maybe 
> these effects come into play.  To first order, though, tracking is very 
> good and that's the main thing.

I had also quite good tracking but the overshot/ringing
at start of retrace caused tri wave be a bit messy at higher
frequencies! Could be filtered by small pf cap ofcourse! 

Well, Ian was it 1,5 years ago or not??

REg
KD