[time-nuts] 'CPLDs for clock dividers' Thread

Bob Camp lists at rtty.us
Mon Jan 6 19:10:19 EST 2014


Hi

The other reasonable question that may be asked is - at what offset from carrier?

I’d expect the floor to cut in by 10 KHz offset. The numbers at 1KHz might be 6 db worse than the floor. Past that depends a *lot* on how fast the edges are on your drive signal. If all goes well, you could be at -145 dbc at 100 Hz offset. You could be 10 or 20 db worse. 

Bob
 
On Jan 6, 2014, at 6:07 PM, Bob Camp <lists at rtty.us> wrote:

> Hi
> 
> You can get into the -154.9 dbc / square root hertz to -164.9 dbc / square root hertz 
> 
> Since we’re talking about phase noise I assumed the units were the ones normally used. Typing all the square root hertz stuff takes a while. 
> 
> It’s been a while since I’ve seen phase noise dimensioned in eggs ….
> 
> Bob
> 
> On Jan 6, 2014, at 12:45 PM, Ulrich Bangert <df6jb at ulrich-bangert.de> wrote:
> 
>> Bob,
>> 
>> I appreciate your postings a lot but can you please explain what property
>> you are referring to with a sentence like
>> 
>>> you can get into the high 150’s to low 160’s on a 10 MHz
>> 
>> Using numbers without units (maybe: quail eggs per sqare inch ?) makes it
>> difficult to understand what you are going to say even for experienced time
>> nutters.
>> 
>> Brent,
>> 
>>> Precious little to add to this, just to confirm that 
>>> back in another life at Watkins Johnson (early 90's), 
>>> we used CPLD's for low phase noise dividers all the time.  
>>> My work at the time was focused on everything but the divider.
>> 
>> Ok, but how much different input signals did you have for one CPLD? If your
>> answer is "1" then you have given youself the explanation why they worked
>> ok.
>> 
>> Best regards
>> Ulrich
>> 
>>> -----Ursprüngliche Nachricht-----
>>> Von: time-nuts-bounces at febo.com 
>>> [mailto:time-nuts-bounces at febo.com] Im Auftrag von Bob Camp
>>> Gesendet: Montag, 6. Januar 2014 13:28
>>> An: Discussion of precise time and frequency measurement
>>> Betreff: Re: [time-nuts] 'CPLDs for clock dividers' Thread
>>> 
>>> 
>>> Hi
>>> 
>>> If you disable all the internal clocks (normally fairly easy) 
>>> and your supply is clean and it’s a modern high speed part, 
>>> you can get into the high 150’s to low 160’s on a 10 MHz 
>>> output with a CPLD. 
>>> 
>>> If you have one of those wonderful old designs where the 
>>> charge pump clocks (or what ever) stay on all the time, you 
>>> will be in the 120’s to 130’s. 
>>> 
>>> Bob
>>> 
>>> On Jan 5, 2014, at 9:11 PM, John C. Westmoreland, P.E. 
>>> <john at westmorelandengineering.com> wrote:
>>> 
>>>> Hello All,
>>>> 
>>>> I was looking at the archives - what was the outcome of this:
>>>> 
>>>> Thanks to everyone for their advice.  I bought a CoolRunner II 
>>>> development board (only $39!) and will let you know how it goes.
>>>> 
>>>> Matt
>>>> 
>>>> On Wed, Feb 3, 2010 at 10:59 AM, Matt Ettus <boyscout at gmail.com 
>>>> <https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts>> wrote:
>>>>> * Does anyone have any experience using CPLDs for very low phase 
>>>>> noise
>>>> *>* dividers?  You can get an XC9536XL from Xilinx for 
>>> around $1, and 
>>>> I
>>>> *>* thought it would make a good divide by 2 through 10 device.
>>>> *>>* Matt*
>>>> 
>>>> A lot of the discussion focused on the difficulties of 
>>> downloading the 
>>>> tools for Altera or Xilinx - the Max II family from Altera was 
>>>> recommended - but there was no apparent outcome or 
>>> resolution to this 
>>>> thread - seemingly.
>>>> 
>>>> Does anyone have that CPLD recommendation?
>>>> 
>>>> Thanks,
>>>> John Westmoreland _______________________________________________
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