New idea sawtooth generator (fwd)

Rick Jansen sscprick at
Wed Jul 12 22:11:02 CEST 1995

In message <199507121813.LAA18032 at> Don Tillman writes:
> You can also compensate by tweaking the curve of the exponential
> current source.  In fact, bulk resistance being what it is, this
> effect might even by overcompensated for.  Y'never know until you
> check. 
> The other problem is the saw-to-triangle converter (basically a
> full-wave rectifier) will glitch over the reset time.

Compensation of the reset time with the potmeter in series with the
cap has the effect that the amplitude of the saw is a bit lower
at higher frequencies. As the saw is offset with a fixed voltage
there will probably be glitches in the converted waves. Unless
you also make the offset a bit smaller at higher f...

> The problem I see with this dual-sawtooth approach is that it's
> effectively the same as making a triangle wave VCO to start.  By that
> I mean if you build a simple triangle wave VCO (OTA and Schmitt
> trigger), and switch between inverted and non-inverted polarities on
> the Schmitt trigger output, you've done the same thing but it's a lot
> simpler.  (And it only uses only one capacitor so you don't have to
> worry about subharmonics if one of the caps drift.)

Hmm.. I switched from a triangle generator to saw because I thought
sync was easier to implement. Will look into this again, as the
exact reasons elude me right now. I just thought this a neat trick,
it IS a saw generator, but with the shortest possible reset time...

Do you think it's audiable if one period of the saw is a bit (say 1%)
shorter than the next...? 

Rick Jansen
rick at
S&H's a module and s&h's looking good

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