[sdiy] Help, I'm Desperate! (Charge Injection with DG408)

Guy McCusker guy.mccusker at gmail.com
Wed Dec 12 17:27:59 CET 2018

On Wed, Dec 12, 2018 at 4:21 PM <rburnett at richieburnett.co.uk> wrote:

> One switch's control signal has duty ratio ramping down from 100% to 0%,
> whilst another switch's control signal has duty ratio ramping up from 0%
> to 100%.  (Use whatever control law you want for the crossfade:  Linear,
> Constant power, etc...)  Only two PWM streams are active and need to be
> generated at any given time so shouldn't be too demanding on a low-end
> micro.

Thanks for spelling it out.

This is exactly the control regimen that the Richter circuit achieves
with the LM3914 and dithering oscillator. In that circuit the LM3914
outputs were used to drive vactrols which attenuate the input to the
summing amplifier but it seems to me one could use them to drive the
switches in this design instead. Richter's oscillator runs at 44kHz,
which is presumably fast enough for this design too?

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