Jitter methodology
I will try to present an rough idea on how a jitter measurement could be
made. I take the risk of repeating things that were said in last week's
meeting, or taking a step in a completely orthogonal direction to where the
discussions were going.
For the TX test, we could use something similar to what has been proposed in
the dispersion penalty test for 1550 nm
(www.ieee802.org/3/ae/public/nov00/ohlen_3_1100.pdf, p. 6,8,11). The TX is
tested with a golden RX where sinusoidal jitter can be added to the
recovered clock. Then the BER penalty with jitter is then measured.
For the 1550 nm case, TP3 would be the compliance point. The reason for this
is that in general any two 40 km G.652 single-mode fibers are much more
equal than any two transmitters. In other words, the amount of jitter that
the fiber will add is a strong function of transmitter (D.U.T.) properties
that are difficult to measure at TP2 and might not have a simple relation to
the amount of jitter added.
For the RX test a similar approach is taken. A stressed eye is still used to
create DCD, but in addition sinusoidal jitter is added to the stressed
signal. Here, the frequency of the sinusoidal jitter has to be higher than
the maximum corner frequency of the PLL used in the RX (D.U.T.). The
stressed sensitivity of the RX (D.U.T.) is then measured and compared to the
spec.
So, how would these measurements be tied together and fit into the jitter
budget?
In TX test, the amount of sinusoidal jitter injected in the golden receiver
corresponds to the margin that the non-golden PLL in a real device will
need, plus the jitter that the non-golden PLL in a real device could have.
In the RX test, the amount of jitter introduced by the stressed eye
generator and the sinusoidal jitter input corresponds to what the jitter
budget allows for the transmitter and the fiber, e.g. the maximum jitter
that could be seen at TP3.
I deliberately left out any numbers. Instead I am hoping to get some
comments on the methodology.
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