[time-nuts] Distribution amplifier (again!) - now mostly ok but has gain peaking

Anders Wallin anders.e.e.wallin at gmail.com
Fri Sep 22 08:13:42 EDT 2017

On Sat, Jan 28, 2017 at 5:53 PM, Mattia Rizzi <mattia.rizzi at gmail.com>

> Have you tried to use clock distribution components like 5PB1108? You could
> use that to distribute the LT1711 output to the output stages
> *independently*. You could use also 5PB1108 as output stage as well (but
> this depends on your output voltage level), I got like >3V/ns on a 50ohm
> with 6 outputs tied together. For fine alignment a variable capacitor (or
> RC filter) at the output stage's input pin may do the job.

Hi Mattia, everyone,

I now had time to assemble a few distribution amplifiers using IDT5PB1108
(see [1], left side).
With my skills in length matching the traces (using Kicad) I still get
around 200ps peak-to-peak output skew between channels.
The chip datasheet spec is <50 ps pin-to-pin skew.

So now I tried adding a trimmer-cap on the input of the output-buffer.
I tried both 50pF and 10pF, but it seems 10pF gives a 500ps delay-tuning
range which is sufficient.
When tuning all channels to within 20ps P-P one day, I then got 50 ps P-P
when verifying this the next day.
Using BNC-cables and an SMA-BNC adapter on the output might not be the
greatest choice for picosecond repeatability...

I did the measurements with a 53230A and the reported values are the
average of 30-60 s of 1PPS pulses.
Some images with the board and results here:

I also opened up a commercial pulse-distributor, and it has the same kind
of trimmer-caps before the output-stages.
It measured 28 ps peak-to-peak among 16 output channels.

I will incorporate a trimmer-cap into the next version of the "PDA" design
and publish on ohwr - when I have time..

[1] https://www.ohwr.org/attachments/5339

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