[sdiy] Help needed with ASM based VCO

[Ian Fritz]

At 12:47 PM 2/18/06, René Schmitz wrote:

>That may be, I never investigated this deeper with circuits where the cap 
>is part of an integrator. Maybe the capacitive load of the probe does eat 
>up some of the phase reserve.

Well, I'm using a 20MH scope, so I don't expect to get a perfect picture of 
these rf transients.   But if I have one probe on the output and place the 
second probe somewhere else I do see some change in signal.  Thinking about 
it now, I should have put both probes on the output!


>>After buffering with a good opamp the signal is quite clean.  Note that 
>>these particular oscillations are at >10 MHz.  I require a clean signal 
>>for waveshaping also, especially for something like my 5Pulser, which can 
>>have problems with extra triggering.
>
>It is a matter of taste.

Absolutely.  Either method can work very well.


>And I don't doubt that you get a decent signal out of your circuits. Its 
>just that MOSFETs for me never really worked quite the way I liked it to be.

Understood.  I had quite a bit of a problem minimizing the extra 
spikes.  Going to the VN0104 helped a lot, because of its low capacitance I 
think.


>I like the signal to be as clean as possible from the start. But to really 
>do that you have to tweak the component values a bit for each incarnation 
>of a circuit. (JFETs have component variations...) I've often added little 
>series resistors to the discharge circuit to get a cleaner signal out.

Wow.  Now that's what I call tweaking.  :-)


   Ian