Hi In addition, the input to the ADC has it’s own noise issues. If you have a really clean clock (or a poor ADC), the noise floor of the input may dominate the noise floor.
Bob > On Sep 26, 2020, at 12:28 PM, jimlux <[email protected]> wrote: > > On 9/26/20 8:10 AM, 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? > > To a first order, the ADC is like an ideal multiplier/mixer - phase noise on > the clock contributes to phase noise on the sampled data by reciprocal > mixing, just like a mixer. > > > >> 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? >> Thanks! >> John >> _______________________________________________ >> 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. _______________________________________________ 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.
