On Sun, 25 Aug 2019 13:59:15 +0200 Gerhard Hoffmann <dk...@arcor.de> wrote:
> Am 25.08.19 um 10:52 schrieb Hal Murray: > > att...@kinali.ch said: > >> As you have always two channels, I would recommend to use two mixers fed > >> with > >> an LO that is 90°C out of phase to get I and Q components. > > How does that compare with running a single channel twice as fast? > At low enough frequencies, the two ways are identical in performance > and linked by the Hilbert transform. Yes, exactly. This is the ideal case where it doesn't matter whether one takes n-times more samples per second by sampling faster or by using n-times as many ADCs. The I/Q sampling is only meant as a way to possibly decorelate noise that is not inherent in the signal. > At high enough frequencies, ADC performance starts to suffer. One gets > a smaller "effective number of bits" ENOB as sample rate and/or input > frequency rise. This starts quite low already, unfortunately. There are several sweet spots where SNR vs sampling speed is optimal. These happen usually when a certain ADC technology comes to its limits. Fortunately, these limits, and the associated sweet spots are moving upwards as time and technology progresses. A few years back, when we designed the sine-exitacion based TIC[1], the sweet spot for pipeline ADCs was somewhere around 100-120MHz. Attila Kinali [1] https://ohwr.org/projects/r19-tdc-del-a/wiki -- It is upon moral qualities that a society is ultimately founded. All the prosperity and technological sophistication in the world is of no use without that foundation. -- Miss Matheson, The Diamond Age, Neal Stephenson _______________________________________________ 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.