[sdiy] Idea - Triangle wave DCO core

[Magnus Danielson]

On 03/14/2012 11:15 AM, Tom Wiltshire wrote:
> It occurred to me today that you could fairly easily build a triangle core DCO. This wouldn't use a reset pulse, but would instead use a bipolar DAC.
>
> You'd simply output a charging CV from a DAC to an integrator. After half a cycle has been timed by the uP, it switches the DAC charging CV to the opposite polarity. And so on. Instant triangle wave at known frequency.
>
> Has anyone ever done/seen anything like this?

Elka Synthex is the closest I think. It used a counter for a sawtooth 
base, and then digital waveshaping for triangle/ring-mod. It's not the 
integrator that you describe.

> Presumably once you'd got the basic version working, you could tweak the rise/fall CV calculation to get variable waveforms between ramp(ish) and triangle. Aside from that, I can't see any massive advantages beyond simplicity.
>
> What do you think?

If you have enough bits, you can bundle the oscillator strength into the 
mix. In essence, with a single DAC and a single integrator you can do 
multiple oscillators, since you mix them in the digital domain.

Cheers,
Magnus