Hi
> On Sep 26, 2020, at 7:22 PM, Magnus Danielson <[email protected]> wrote: > > Hi John, > > On 2020-09-26 17:10, John Ackermann N8UR wrote: >> We know that phase noise scales with frequency, so if you multiply >> frequency by 10 you get a 20 dB increase in noise. >> >> What I don't fully understand is how that relationship works with >> other than simple multiplication/division. >> >> For example (and my real life concern), if I have an analog to digital >> converter that is clocked at 122.88 MHz and know the phase noise of >> that clock signal, what do I know about the effective phase noise when >> the ADC is receiving a signal at, e.g., 12.288 MHz? >> >> In other words, if I were to measure the phase noise at the output of >> the ADC when fed a high-enough quality 12.288 MHz signal, would I see >> something like the 122.88 MHz phase noise, or something better due to >> the scaling by 10? > > In this case, your 12.288 MHz phase-noise will be augmented with the > scaled-down version of the 122,88 MHz phase-noise. The trick being used > is to actually let the sampling clock of the ADC be a transfer clock > such that it samples a reference also, at which time one subtracts the > phase-data from the reference, most of the transfer clocks noise cancels > out, and it does so fairly well as it have common integration time > between the channels, so you avoid the decorrelation that DMTD normally > suffers from. The second trick being used is to use a second pair of > ADCs to make ADC deficiensies cancel out too, as the DUT and REF is > common mode and the individual ADC noise contributors can be averaged out. > If you are going to do the “cancel out” process, a dual ADC with a common clock interface is a really good idea. Not all dual ADC devices have that feature…… Bob > Now, as you decimate data etc. you still have the issue of ADC > resolution, as that has a tendency to loose weak side-bands. The > non-linearity is kind of peculiar actually. > > I recommend you to dig up Sam Stein's papers on his phase noise > development. I think you will find them a good read and help you with > your understanding. > > Cheers, > Magnus > > > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
