[time-nuts] reference oscillator input circuit

[Robert Darlington]

Just an FYI guys, I'm pretty sure the 3rd circuit down on the Wenzel page is
identical to the input circuit for the TAPR TADD-2 frequency divider.  The
TADD-2 adds a transformer and load resistor.  Schematic is in the manual
here:

http://www.tapr.org/~n8ur/TADD-2_Manual.pdf

-Bob

On Wed, Dec 8, 2010 at 8:46 AM, John Ackermann N8UR <jra at febo.com> wrote:

> Wenzel has some discussion and circuits at:
> http://www.wenzel.com/documents/waveform.html.
>
> The Shera GPSDO made clever use of the input circuit of a 74HCT4046 PLL
> chip for squaring.
>
> John
> ----
>
>
> On 12/8/2010 10:31 AM, jimlux wrote:
>
>> I'm looking for suggestions on a general circuit that can be used to
>> receive an external frequency reference (nominally a real clean sine
>> wave at, say, 10 MHz, although up to 100 MHz is possible) and turn it
>> into a "real clean" square wave. Galvanic isolation is a plus (a
>> transformer or capacitor would probably do that).
>>
>> I was thinking about rummaging through the schematics for test equipment
>> reference inputs (since they've already "solved" the problem, eh?), but
>> any other ideas would be welcome.
>>
>> I've scanned the archives of time-nuts, and while we have a fair amount
>> of discussion on how to square up the 1Hz (or 100Hz) in a phase
>> noise/ADEV setup, not so much on what to do with the 10 MHz. Rick has
>> commented that you don't want to use a comparator. I have the papers by
>> Dick, et al, and Collins, as well as all the others.. they tend to be
>> looking at the low frequency problem, although the analysis is certainly
>> applicable.
>>
>> I don't know that I'm looking for the whole multiple limiting stages
>> scheme in any case.
>>
>> Oh, as far as performance.. Say the need is to not horribly degrade a
>> good quality crystal oscillator... here's a typical set of specs:
>> 76 MHz
>> 1Hz <-90dBc
>> 10Hz <-110dBc
>> 100Hz <-120dBc
>> 1k-100k <-125dBc
>>
>> Adevs of the oscillator run from 5E-12 at 0.1 sec, down to 1E-12 at 10
>> sec, and back up to 2 E-12 at 1000sec.
>>
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>
>
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