[time-nuts] Frequency Comparator Ideas needed
Dan Kemppainen
dan at irtelemetrics.com
Thu Aug 11 20:10:58 UTC 2011
Hi All,
I could clairify things a little. My event of interest is basically a
fast frequency shift of a signal that drifts between 1800 and 2600Mhz.
There is slow drift of this signal of many hundreds of Mhz, with fast
frequency shifts of approximatley +/- 150Khz. I believe that the
150Khz shifts are nearly instantaneous, but currently have no way to
measure exactly how fast they occur. Slow drifts are corrected for by
a loop in the down converter.
Currently there is a first down conversion stage to ~900Mhz. This is
then down converted again to an arbitrary frequency band (50Mhz in
this example, but this could be moved from ~10Mhz to 200Mhz or greater).
Obviously it would be advantageous to keep the low frequency band as
high as possible, at least when trying to determine when the frequency
shifts occur with any digital detectors. Probably for any analog
detectors also.
Bob,
Obviously I'd like to get as close to the real zero crossing as
possible, but I'm sure I don't need 0.6pS. If I could tell if the
signal was within maybe +/- 15 or 20Khz, it may be acceptable. I could
always double the frequency then down convert to increase the
deviation. Basically, I have another timing device that will record
every single event within 5nS, as long as they don't exceed ~1e6
events per second. That's the unit I'll feed the signal into, and what
I need to keep happy.
I did just learn about Gilbert cell mixer that works from DC to 500Mhz
yesterday. I didn't realize they were available with that wide of a
bandwidth. With this part as an option, it may be possible to do a
quadrature detection around the several hundred Mhz range. That way
subsequent low pass filters can have fairly high bandwidth. I'm sure
the results here will probably be noisy, but maybe still acceptable???
However, I'd still like to it digitally if possible. Maybe even adding
a second VCO with high modulation bandwidth to use a PLL with to track
the input signal. Maybe then a phase detector comparing that PLL
output and the reference signal and some high speed digital processing
could prove useful. Not sure tho, still need to think about that.
Probably would end up needing some multi Ghz flip flops to make that
work...
Ultimately this may not be possible digitally, but I thought if anyone
here knew of anything it would be here...
Thanks all!
Dan
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