the only problem with that CMOS freq. multiplying circuit's that the
threshold of the inputs has a thermal noise component = jitter [phase
noise]
73
KJ6UHN
Alex
On 1/19/2020 11:31 AM, Mark Haun wrote:
Hi Jim,
On Sun, 19 Jan 2020 10:35:42 -0800
jimlux <[email protected]> wrote:
On 1/19/20 9:29 AM, Mark Haun wrote:
On Sun, 19 Jan 2020 09:37:39 -0500
Bob kb8tq <[email protected]> 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 -- [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.
