Thanks for all your thoughts on the subject. Let me play back what I
have learned and how it may apply to my challenge. One of my first
applications is to use a 10MHz output to phaselock a VCXO master clock
in a radio transceiver. The VCXO is the Christek CVHD-950 which has a
noise floor of -164dBc and is -86dBc at 10Hz. The source I want to use
is the Jackson Labs GPSTCXO which has a noise floor of -155dBc and is
-73dBc at 1Hz and 103dBc at 10Hz. i did a quick survey of the phase
noise specs on various Jackson products that claim to be ultra low phase
noise and found similar numbers. One was -100dBc at 1Hz but only
-145dBc at 100KHz. Another was down -90dBc at 1Hz and -160dBc at
100KHz. It would appear that even the best parts I could find quickly
would not merit the fancy analog gizmo and that a good stiff logic
buffer would work. Next I went to IDT to find the best logic buffer I
could find. I am looking at the IDT 74FCT38072 2 channel clock driver
for PPS. It can drive about 50mA if needed with 1nS rise and fall
times. The one I am looking at for 10MHz is the ICS553 4 channel clock
driver. This one is good for 25mA drive and they actually give a
typical output impedance spec of 20 Ohms. With a 3.3V supply, it has
1nS rise and fall times and a little faster with a 5V supply, 0.7nS and
35mA drive. To make a sine wave should I use one of the 4 ports on the
4 port driver to input to the filter or should I try to hook the filter
input directly to the clock driver input?
Are there tried and true 10MHz filter circuits or is that a non issue?
After the filter would come the video amp set up for a 50 Ohm drive and
into a splitter. That sound simple enough. What am I missing?
Tom
On 9/26/2013 3:05 PM, Bob Camp wrote:
Hi
How clean is your clock source? If you have something that is -150 dbc at 1 Hz, then you
probably need some fancy analog gizmos. If you can make do with "only" -110 to
-120 dbc/Hz at 1 Hz, then properly driven LVC CMOS will do just fine. That's true for a
square or a sine output. Since you pretty much can't find an OCXO better than -120 at 1
Hz, I'd bet you'll be ok. 5 volt logic will be a little more quiet than 3.3V. More or
less faster is quieter as long as you stay with saturated silicon CMOS. Change materials
and all bets are off.
For square wave cable drive you can parallel up a couple of the '125 or '126
gates to get how ever much power you want to put into the cable. You can source
or load terminate (or both). If you source and load terminate, your logic
levels will be 1/2 the output. With either source only or load only termination
you can get full swing logic levels. More drive will always be required with
load termination (you are putting current into 50 ohms).
Logic IC's are cheap, easy to use, and simple to find. A low voltage single
supply drives them and they aren't current hogs unless heavily loaded. What's
not to like?
Bob
On Sep 26, 2013, at 1:28 PM, Tom Minnis <tom_min...@att.net> wrote:
I am looking into various degrees of craziness. The source is CMOS and there
are plenty of 1 in to N out parts designed to drive clocks on a PCB but not
much is said about driving clocks on to a random length of coax to another
piece of equipment and what additional precautions that might warrant. I am
also considering making a sine wave output and maybe other frequencies.
Tom
On 9/26/2013 4:34 AM, Bob Camp wrote:
Hi
Standard high speed CMOS logic works pretty well. How crazy are you trying to
get?
Bob
On Sep 26, 2013, at 1:48 AM, Tom Minnis <tom_min...@att.net> wrote:
I am working on a small clock distributor and wanted to get some ideas on what
works best for 10MHz and 1PPS driver circuits. I remember sifting through the
archives a year or so ago and tripped on some discussion of this but I can't
find it anymore.
Tom
_______________________________________________
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
_______________________________________________
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
_______________________________________________
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
_______________________________________________
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
_______________________________________________
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
