[sdiy] There was a crooked man who had a crooked oscilloscope probe.

[Grant Richter]

It sounds to me like you have not EQed your o-scope probes in a while.
Everything you mention is happening around transients, which is what  
the little EQ adjustment on the scope probe is for, to set the  
frequency response of the probe so it is flat.

> I have a small "problem" with my saw-core VCOs: after the  
> integrator resets,
> the integrator output takes a finite time to straighten out.  This  
> gives the
> final sawtooth output wave a bit of curvature near the top.  The  
> slope is a
> bit too steep for the first fraction of a volt, and then it  
> straightens out.
> I've tried everything I can think of to eliminate it, but nothing  
> has any
> effect.  It doesn't seem to be related to the comparator RC time  
> constant,
> or any other little caps, or the mode of resetting, and it is not  
> reproduced
> in SPICE.  One thing I haven't tried is changing the integrator  
> cap.  I'm
> using a 1nF, C0G/NP0 ceramic cap.  I have some 1nF metallized  
> polypropylene
> film caps I could try, but I haven't yet.
>
> Interestingly enough, the effect more or less disappears at high  
> frequencies
> (it is largely undetectable on the scope above the audio range).
>
> Also, the pulse waves derived from the saw have a little downward- 
> pointing
> "hook" at the beginning of each negative half-period.  I can't see  
> how the
> two phenomena could be related, since the pulse wave is just a  
> comparator
> output, and the saw is only setting the threshold voltage.
>
> I'm using all TL07x opamps in the circuit (except for the saw  
> comparator,
> which is LM311), and I'm wondering if this has something to do with  
> it.  In
> both cases, a TL07x opamp is generating a sharp falling edge.   
> Could it be
> that TL07x opamps do something funny when they generate falling edges?
>
> If anyone has any insight into this phenomenon, I'd love to hear  
> about it.
>
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