[time-nuts] question Alan deviation measured with Timelab and counters

Bob Camp kb8tq at n1k.org
Sun Jan 25 13:01:03 EST 2015


The approach in the original NIST paper below was sort of a “best guess” about how to do the limiting and filtering. When the paper was presented, a number of us questioned how that part of the circuit was arrived at. The conversation more or less ended up with “that’s something we can investigate further”. The Collins paper (and Bruce’s work based on it) is a much better way to look at the 10 Hz squaring process. At 10 MHz, that stuff is not needed.


> On Jan 25, 2015, at 10:44 AM, Stéphane Rey <steph.rey at wanadoo.fr> wrote:
> Hi everyone.
> Many thanks for your very useful comments.
> I had already seen most of the documents you were pointing but not on the
> collins and Bruce discussion around the multistage filter. However I've
> already seen this approach in the document from Allan
> (http://tf.nist.gov/timefreq/general/pdf/84.pdf)
> At first I had in mind to square the 10 MHz but this is the aim of the
> evaluation board to evaluate various architectures. So I will implement
> several squarers including the Collins Approach both at 10 MHz and 100 Hz
> and all the blocks will have input and output connectors so that I will be
> able to test several layouts.
> I will show you the final design.
> Cheers
> Stephane
> -----Message d'origine-----
> De : time-nuts [mailto:time-nuts-bounces at febo.com] De la part de Charles
> Steinmetz
> Envoyé : dimanche 25 janvier 2015 08:08
> À : Discussion of precise time and frequency measurement
> Objet : Re: [time-nuts] question Alan deviation measured with Timelab and
> counters
> Stephane wrote:
>> I'm now trying to evaluate various architectures of 2-channels squarers 
>> and a DMDT. For that I'm designing a PCB with 4 squarers :
>> simple 74ac04 gate biased at VCC/2, a LT1016 comparator, the transistor 
>> based differential amplifier from Winzel and the one from Charles.
> Note that squaring a 10MHz sine wave and squaring a 10 or 100Hz mixer output
> are two very different tasks.  If you start at baseband, a Collins-style
> multi-stage limiting amp is a great benefit.  That is generally not
> necessary if you start at 10MHz (or if you do use a Collins-style limiter it
> needs far fewer stages).  All of the squarers you mention work well at
> 10MHz, but not as well at baseband.
> The LT1719 is easier to apply and faster than the LT1016.  You may want to
> use that instead of the 1016.  The LT1719 and LT1715 datasheets show the
> simplest possible implementation (see below).
> The MPSH81 devices in my version are available in surface-mount
> (MMBTH81) if that is more convenient.  Other fast transistors will also work
> (BFT92, BFT93, BFG31).
> Best regards,
> Charles
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