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. 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 -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.