[sdiy] SAW core VCO flyback time

[Donald Tillman]

> On 31 Aug 2016, at 19:25, rsdio at audiobanshee.com wrote:
> 
>> Could someone describe "that lovely PWM vibrato sound" for me? I'm mostly asking why it's possible with sawtooth and not triangle.

> On Aug 31, 2016, at 12:11 PM, Tom Wiltshire <tom at electricdruid.net> wrote:
> 
> On a ramp wave, the pulses get wider in one direction only, whereas with a triangle, they get wider in both directions symmetrically.
> 
> In the ramp wave case, this means that there's a phase shift going on. And a changing phase shift is a frequency modulation, so it warbles.
> 
> At least, that's my understanding of it. If that's not right, perhaps others can correct me.

That's right.

More specifically, with a variable duty cycle pulse wave, the 0 degree cosine (or 90 degree sine) phase of the fundamental component is aligned with the midpoint of the high section of the pulse.

The midpoint of the high section of a triangle PWM stays in place, while the midpoint of the high section of a sawtooth PWM moves 180 degrees over the 0% to 100% PWM range.

  -- Don

--
Don Tillman
Palo Alto, California
don at till.com
http://www.till.com