[SI-LIST] Re: Fw: Anritsu PPG output glitches

 
HWG,

I cannot view any attached slides, and so can only make general
comments. Please feel free to send me the detailed slides at
martin.murphy@xxxxxxxxxxx and we'll be better able to resolve your
specific questions. If you let me know where you are located, I can also
get you in contact with your local applications engineer who is much
more likely to help you resolve any questions than an open forum like
SI-LIST, since he has access to our design teams. 

While splitting/amplifying/switching data and xdata outputs separately
should generally be OK, good design practices are still required as with
any high performance instrumentation. Most BERT PPG outputs are designed
to drive 50 ohm loads through reasonable quality cables, and data/xdata
outputs are usually driven through independently controllable output
amplifiers. Importantly, most PPG outputs (including the MU181020A) can
be turned off while changing output connections, DUTs, etc. This helps
protect the output stages against unknown/uncontrolled conditions, and
if you are not using these capabilities in your testing, that would be
my first recommendation. 

I'll try to comment further when I see the test set-up and see what
"noisy" means from the PPG.

Regards,
Martin Murphy


-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
On Behalf Of hwg
Sent: Friday, April 23, 2010 9:57 AM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Fw: Anritsu PPG output glitches


Hello SI gurus,


I was on si-list years ago when I was doing some optical line card
hardware design.  I've been doing other things recently, but a colleague
of mine is having an issue, and I wonder if any of you have seen
anything like this.

We have a production test environment for 10Gbps lasers, which uses
Anritsu pattern generators to generate signals to drive the lasers.

We share a single PPG among multiple test fixtures, by
- using DATA and DATA_BAR to drive separate fixtures
- using an external 3db splitter (Picosecond Pulse) to split one of the
outputs

In total, we have 3 PPG's driving 8 test fixtures.  There are external
RF amplifiers, RF switches and bias-Tees connected as well.  (Details
are in the attached slides.)

We're seeing that occasionally, the output of the Anritsu PPG gets
"noisy" (that the best I can describe it; see the pictures in the
attached slides).

This never happened, over a 5-year period, until we recently upgraded
our Anritsu PPG's to a new model.  (MUT181020A)

I suspect something with the output driver of the new Anritsu PPG.
Perhaps when we switch the RF switches, there is a momentary impedance
discontinuity, and thus a reflection back to the PPG, which puts its
output into a "bad" state. 

The only way to recover the PPG so it generates a clean output again is
to power cycle it.

Has anyone seen anything like this before?  Any suggestions on how to
solve it would be greatly appreciated.

- hwg


      


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