[sdiy] Variable slope triangle oscillator questions

[Karl Ekdahl]

Hi list

I'm trying to make a variable slope triangle/sawtooth oscillator, using the same basic concept as given here http://www.till.com/articles/VariableSaw/index.html, while this works it makes the output amplitude vary a lot from 50% to 95% (or however close to 100% i can go). 

At 95% (or so) i'm about 1/20th of amplitude of what i get at 50% duty-cycle. I've been trying to come up with a scheme using a simple OTA amplifier to adjust the amplitude of the waveform but so far no luck - i'm just to damn bad at math. 

I realize that the controlling voltage of the amplifier needs to be the rectified sum of the two OTA control voltages (after A3 and A4), i also realize that it needs to have some kind of exponential properties. I guess i just don't understand how to calculate what kind of slope is necessary. Any help for the math-tarded?

Karl

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