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

[Antti Huovilainen]

On Mon, 7 Sep 2009, David G. Dixon wrote:

> 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?

Can't say about "blindingly obvious", but when designing a tube VCO (still 
on drawing board), I used a max(a, b) circuit that allowed very simple 
solution for the glitch.

Connect two transistors as emitter followers with the emitters tied 
together. Feed the second transistor with inverted signal. By connecting a 
small capacitor to the output, you can easily control the slewrate 
asymmetrically. The transistors can charge the capacitor very fast, but 
the resistor/current sink at the output has only finite current available 
for discharging it. Now arrange input sawtooth polarity so that the glitch 
at triangle output goes down and adjust resistor/current sink and 
capacitor to taste.

Antti

"No boom today. Boom tomorrow. There's always a boom tomorrow"
   -- Lt. Cmdr. Ivanova