[time-nuts] Divider circuit for Rubidium Standard

Bryan _ bpl521 at outlook.com
Mon May 18 10:19:54 UTC 2015


Hi Bob:

i assume when you are referring to the comparator you are referencing the ADCMP600 or MAX999 that is used to clock shape the input for the logic dividers etc and the 74AC541 bus drivers.

Could one modify the circuit to use a low noise LTC6957 to clock shape and then divide down using the existing circuitry. I would assume this would offer a greater improvement in phase noise?

Cheers
 

-=Bryan=-

> From: kb8tq at n1k.org
> Date: Fri, 8 May 2015 17:19:59 -0400
> To: time-nuts at febo.com
> Subject: Re: [time-nuts] Divider circuit for Rubidium Standard
> 
> Hi
> 
> I guess the simple answer is “when you measure them that’s the result”. 
> 
> The slightly more complex answer is “fast silicon CMOS is indeed good, other
> types may require further analysis”.  In general the faster stuff is better than 
> the slower CMOS. 
> 
> Deeper into it you get to the fact that the gate is optimized for one input swing range, 
> speed and consistent (short) delay. The amount of time that anything in a CMOS gate spends
> in-between “on” and “off” if very short. If you look at the time it’s hooked to a rail as noiseless (= 
> quiet supplies), then the time noise can get into the output is quite short. Short time = little noise.
> 
> You could go further with fancy tools.
> 
> Bob
> 
> 
> > On May 7, 2015, at 11:09 AM, Attila Kinali <attila at kinali.ch> wrote:
> > 
> > On Wed, 06 May 2015 18:09:03 -0700
> > "Richard (Rick) Karlquist" <richard at karlquist.com> wrote:
> > 
> >>> A standard input on a frequency counter is not a very demanding thing in the hierarchy of
> >>> TimeNut signals. You can drive any of them with some pretty simple logic gate based
> >>> circuits. No need to spend a lot of money.
> >> 
> >> Logic gate, yes.  Comparator, no.
> > 
> > This reminds me a lot of a similar discussion a couple of weeks ago.
> > (where the issue boiled down to noise bandwidth)
> > 
> > What is the problem with a comparator vs a logic gate?
> > What makes the logic gate supperior?
> > 
> > 			Attila Kinali
> > 
> > -- 
> > It is upon moral qualities that a society is ultimately founded. All 
> > the prosperity and technological sophistication in the world is of no 
> > use without that foundation.
> >                 -- Miss Matheson, The Diamond Age, Neil Stephenson
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