Hi Jim, On Sun, 19 Jan 2020 10:35:42 -0800 jimlux <jim...@earthlink.net> wrote: > On 1/19/20 9:29 AM, Mark Haun wrote: > > On Sun, 19 Jan 2020 09:37:39 -0500 > > Bob kb8tq <kb...@n1k.org> wrote: > >> Is your intended application tolerant of spurs at 16 and 32 MHz? If > >> not, do they need to be in the 90 dB down vicinity (= the SFDR of > >> the ADC) ? > > > > I guess you mean stray coupling between the oscillator, clock > > conditioning circuitry and the analog inputs? (Spurs on the ADC > > clock input shouldn't matter as long as the zero crossings are > > clean and jitter is low.) > > Not exactly. The sampler of the ADC is essentially a mixer, so if > the clock has other signals on it, even at low levels, they can mix > with input signals and show up in band. I had a SDR receiver with a > 49.244 MHz ADC clock that was contaminated by the 66MHz processor > clock (at a very, very low level), and I saw mixing products when the > input to the ADC was a clean sine wave at 112.5 MHz. > > Analog Devices even has an app note on this. > > https://e2echina.ti.com/cfs-file/__key/telligent-evolution-components-attachments/13-109-00-00-00-00-93-58/Impact-of-sampling_2D00_clock-spurs-on-ADC-performance.pdf
Hmmm, so in my case, other residual odd-order harmonics of the 16 MHz input clock which make it through the multiplier will become non-harmonic spurs of the desired 80 MHz, and therefore a potential problem unless filtered out. The analog amplifier scheme will therefore require decent bandpass filtering, mainly against 16, 48, and 112 MHz. One advantage of the Wenzel CMOS-based multiplier is that the threshold behavior of the last inverter [mostly?] gets rid of everything but the selected harmonic. I'm still trying to understand the phase-noise pros/cons of that design using, say, a pair of NC7SZ04 (UHS family) gates, versus a discrete transistor amplifier tuned at 80 MHz, like the common-base design quoted in the original post. Regards, Mark _______________________________________________ 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.