Steve:
I am interested in your bi-phase PDM modulator more...
Why do you need two PDM generator chips to create the bi-phase switching pulses? I would think you could take a single PDM generator chip's output and then create an out of phase pulse by using an RC network and a comparator.
I do not have much time these days, but would like to do this someday.
Thanks,
Dan
W1DAN
hi Dan,
I don't know if an R-C network and a comparator will quite do it, although it might. With this two-phase system, the pulse trains have to be IDENTICAL, or you will end up with the original switching frequency showing up in the filter. And of course, any nonlinearity in triangle (or input to any comparator) will cause major distortion.
You don't actually need THAT many more components to do this. You need an additional driver and associated components. I'm using the floating charge pump system I came up with for the driver.
By using two PWM generators, you get, essentially, double the resolution that you would otherwise get at the ripple frequency. If you ran a PWM generator at 240kHz, the operational bandwidth of the entire PWM generator has to be very high (probably above 10mHz to resolve a 2% duty cycle pulse, without integration). On the other hand, if you run two PWM generators at 120kHz, the whole system's bandwidth requirement is 1/2 that of the 240kHz system (or the resolution is significantly improved), and you still have the advantage of a 240kHz ripple frequency becuase you are combining the outputs (180 degrees out of phase with each other).
Interesting system, for sure! I wouldn't bother with a small-ish transmitter. The added complexity is not worth it.
Regards,
Steve