[time-nuts] HP 5328A Divider / Timebase Output performance

[Bruce Griffiths]

On closer inspection, the TBO output isn't resynchronised to an internal 
clock however a single chip custom timebase divider is used that uses 
both +5V and +15V supplies.
Perhaps this is a high voltage CMOS (or even MOS) part that employs a 
asynchronous  cascading of decade divider outputs?
The output jitter of such a divider could easily be several nanoseconds.

Bruce


Bruce Griffiths wrote:
> The problem could be due to the effect of synchronisation of the 
> divider output to an internal 100MHz clock.
> A close look at the circuit would be required to see if indeed this 
> occurs.
> A quick glance indicates that the TB out signal appears to be always 
> synchronised to an internal clock.
>
> Bruce
>
>
> John Miles wrote:
>>> I would tend to say that the divider is pretty lousy for short
>>> term, but it is all fine for longer runs, right?
>>>
>>> Is this what I should expect from a TTL/ECL divider chain
>>> designed in the '70s-'80s? How would this compare to a modern
>>> divider chain, like the PIC divider or David Partridge's divider board?
>> The 5370 residual plot I mentioned in the other message was taken under
>> similar conditions as you describe, but with a TADD-2 divider, and is 
>> almost
>> 100x better.  IMHO the 5328A solution doesn't look like a good one, 
>> since
>> any inexpensive digital divider should be able to beat it.
>>
>> It's true that factors like trigger levels and attenuator settings 
>> matter,
>> but this will be observed at the tens-of-picoseconds level in my 
>> experience,
>> not at 1ns+ timescales.  Triggering on the correct edge is likely to 
>> be more
>> important.  Try it both ways and see if you notice a difference.
>>
>>> Since I get a straight line pretty much up to 500s or so, do I
>>> conclude that the divider dominates the system noise up to there?
>> That's very safe to say (again, load that residual .tim file and 
>> display it
>> next to your result and you'll understand instantly).
>>
>>> Of course, the 5370A timebase drift has to be taken into account
>>> but is not subtracted on that plot.
>> Slow drift in the 5370 timebase isn't an issue for two-channel ADEV
>> measurements.  If you had a problem involving excessive noise from 
>> either
>> the timebase or trigger circuits at timescales close to your 1-second 
>> tau
>> period, it could degrade the results, but that's extremely unlikely.
>>
>> -- john, KE5FX
>>
>>
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>
>
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