[sdiy] filtering out a saw-reset glitch in a triangle shaper

[Magnus Danielson]

David G. Dixon wrote:
> I'm designing a triangle shaper for the 2164 expo VCO.  This is a new thing
> for me, because all of my previous VCOs are triangle-core.  The basis is a
> simple yet elegant precision full-wave rectifier circuit I found on the web
> somewhere.  To mostly eliminate the saw-reset glitch at the apex of the
> triangle, I'm thinking of filtering the rectifier output with a passive LPF
> with a cutoff frequency of 50kHz (3.3k + 1nF).  That, plus a couple of
> strategically placed 22p caps in the rectifier circuit itself, seems to all
> but eliminate the glitch in my simulations.
> 
> So, here's my question: Is there some reason not to do this that I'm not
> thinking of, or is there some other way to reduce or eliminate this glitch
> which is blindingly obvious to everyone but me?

Well, what you could do, beyond filtering is something I haven't seen 
anyone attempt... blend in just the right amount of the reset-pulse from 
the oscillator reset-cursuit. The signal is there if you only care to 
think of it as an alternative waveform. Purhaps you better lowpass 
filter it for better shaping.

Cheers,
Magnus