Saw to Triangle problem!

[terry michaels]

Message text written by Tadej Bozicko
>
>I have problems with my saw to triangle converter. On the positive peak I
noticed some sort of >clipping, but it's more like nonlinearity of the
diodes. I've tryied several designs, but they are all the >same. Same
clipping at the top, since the negative peak is ok and is sharp as a needle
:). Is that >normal or what? This is especially noticeable at lower
frequencies. Has anyone experianced and >solved similar problem? I've
already tryed several diodes (Ge, Si) and even BE diode in NPN >transistor.
No change :(. I think the problem is not in design (since it work ok in
silmulator), it has to be >something else. Note that I've also tryed
several input amplitudes, but again no change in quality. So I >hope
someone has solution, because this clipping really bothers me a lot. The
design is at:
>http://imola.uni-mb.si/~bozicko/saw2tri.gif
>Even tryed Korg MS20 saw to tri, and Formant saw to tri and they all do
the same clipping. Maybe it >should be that way? Btw. I am using soundcard
as a scope, so maybe there lies a problem (but >sawtooth has no clipping at
all).

Hi Tadej

I believe what you call clipping at the top of the triangle wave is
actually a rounded corner.  This happens at the point your circuit changes
from a non-inverting to an inverting circuit, at the mid point of the
sawtooth wave.  The circuit changes state when the diode begins to conduct.
Tthe diode does not trun on instantaneously, it requires a couple hundred
millivolts voltage change to go from  non conducting to conducting, and so
your convertor changes from non inverting to inverting gradually at the top
of the triangle wave.  Changing diodes won't help, any diode will do this
to varying degrees.

Terry