[sdiy] Driving SSI2144 freq control with PWM from a microcontroller

[Ashlyn Black]

Oh gosh I've definitely joined the right mailing list.


I saw that article a while ago, thought I'd stumbled on a great bit of 
secret sauce and had been planning to use it in future projects.

However after watching that video, I did a little further investigation 
and found that the outputs of the active ripple cancellation topology 
and a passive two pole topology are not only comparable, they are in 
fact identical (at least in the idealized conditions of a simulator.)

Attached is two screenshots, both with 30kHz, 0% to 50% duty cycle 
transitions. The top graphs are the outputs of the active topology, 
middle is passive topology, bottom is an overlay.

...

Sort of feels like I've been duped, ha ha. At least it never made it 
into production and now I have spare microcontroller pins that would 
have otherwise been used as complementary PWM outputs.

Thank you so much for the discussion. :3

- Ashlyn

On 6/11/22 19:37, René Schmitz wrote:
> On 06.11.2022 01:03, Ben Gebhardt via Synth-diy wrote:
>> Interesting discussion!
>>
>> I ran across this EDN article and want to try it out when I get a 
>> chance.  Seems like a good compromise between and RC and full blown 
>> active filter.  Has anyone done this before for synths?  I wonder if 
>> it’s practical for this application.
>>
>> https://www.edn.com/cancel-pwm-dac-ripple-with-analog-subtraction/
>
>
> There is a video about this from Prof. Sam Ben-Yaakov: 
> https://www.youtube.com/watch?v=eJNuHtzOKzY
>
> TL;DW: It turns out it's not adding a real advantage when compared to 
> a passive 2-pole filter. Which doesn't need the inverter, and uses the 
> same number of passives.
>
> BTW, check out that channel if you're interested in power electronics, 
> SMPS and the like.
>
>
> Cheers,
>
>  René
>
>
> -- 
> synth at schmitzbits.de
> http://schmitzbits.de
>
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