[time-nuts] Divider circuit for Rubidium Standard

Bob Camp kb8tq at n1k.org
Wed May 20 17:47:46 EDT 2015


HI

> On May 20, 2015, at 11:55 AM, Richard (Rick) Karlquist <richard at karlquist.com> wrote:
> 
>> 
>> The only gates that seem to do very well are high speed (as in 74AC or faster)
>> silicon CMOS. You need to run them with a fairly clean supply and feed them
>> with a p-p input that matches the supply voltage. Other than that, not a lot
>> of magic. Are they ideal - surely not. Will they hit 2x10^-13 ADEV at 1 second and
>> drop from there as tau increases - yes they will.
>> 
>> Bob
>> 
> 
> Interesting.  Back in the stone age in 1990, 74AC was state of the art.
> As soon as it came out, I used it exclusively for everything that didn't
> require ECL, for which I used ECLinPS exclusively.
> 
> In the 5071A, we used one to square up 80 MHz for the DDS board.  You
> are exactly right:  put in a huge sinewave obtained by good old
> fashioned analog anplifiers and let the 74AC do its thing.

… you actually can do a pretty good job with just a terminated L network feeding the input
to the gate. It’s a high input impedance so driving it from 200 to 1K ohms isn’t all that 
different than 50 ohms. Again - not ideal, but it saves a few parts and some current.

Bob

>  80 MHz
> is pretty much flat out for a 74AC series. The 80 MHz came from a
> 10 to 80 MHz multiplier running from the 10811.
> 
> Rick Karlquist N6RK
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