[time-nuts] Clock Driver Design

[John C. Westmoreland, P.E.]

Tom,

OK - one question for now if that is OK - your video amp - is it base-band
or broadband?

Regards,
John W,


On Thu, Sep 26, 2013 at 11:11 PM, Tom Minnis <Tom_minnis at att.net> wrote:

> 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_minnis at 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_minnis at 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
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