Well a sigma-delta modulator in loose terms is an error amplifier around a quantizer, so you get 1/loopgain rejection of quantization noise (in other words the noise is shaped out in frequency). Resulting in a noise spectrum that converges in 1/N versus 1/sqrt(N) for flat Gaussian noise, versus lobes and nulls for a single sinusoid.
I totally agree that the first step is to reduce the switching residual that is generated, even half a bond wire at say 1 nH is 13 mOhms at 2 MHz, combine that with a power converter running 30% ripple current of a 1A output is 300mA ripple current resulting in 4 mV just on half a bondwire. Equivalently a 10 uF MLCC should be able to hit 10 mOhms at 2 MHz before hitting its SRF. On Sun, Dec 4, 2016 at 5:58 PM, Attila Kinali <att...@kinali.ch> wrote: > On Sun, 4 Dec 2016 16:22:02 -0500 > Scott Stobbe <scott.j.sto...@gmail.com> wrote: > > > If you wanted to be nutty you wouldn't go PWM at all, just like > > fractional-N sythns don't just mash 2 divider values. You would > sigma-delta > > modulate your power stage. I don't know if you can buy one COTS, but > there > > are plenty of papers on rolling your own. > > I guess you are refering to spread-spectrum techniques. > Such DC/DC converters exist, but are usually those with high power > ratings. IMHO it is also not worth the effort, as its main use is > to meet EMI emission requirements. The only application that comes > to my mind where spread-spectrum actually helps are high sensitiv > radio receivers where every spur is a nuisance. For most other > use, and time-nuts use in particular, it is much less useful. > The noise energy is not gone. It is still there, just spread over > a large bandwidth. In time measurement applications, noise is > integrated over time _and_ frequency. Thus even if the noise is > spread over a large bandwidth, the energy will still contribute > to the uncertainty and degrade the ADEV. It will be just harder > to identify as the peak is now much smaller and wanders in frequency. > > It is much better to the design such, that as little as possible > of the switching energy leaks out of the DC/DC converter and filter > out the rest. > > Depending on the application, another possible application is to > sync up the DC/DC converter to the "main" clock source. This makes > the switching noise then coherent to the system, which either makes > it average out completely, or possible to filter it out in the digital > domain using a deep notch-filter in receiver applications. > > > Attila Kinali > -- > Malek's Law: > Any simple idea will be worded in the most complicated way. > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/ > mailman/listinfo/time-nuts > and follow the instructions there. > _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
