Teledyne-lecroy QPHY-ENET Manuel d'utilisateur télécharger pdf (Page 57)

QPHY-ENET Software Option

QPHY-ENET Operator’s Manual Rev G

1000Base-T Master Jitter - Mode 2 without TX_TCLK

Clause 40.6.1.2.5 of IEEE 802.3-2005 says to measure the jitter between the TX_TCLK and the data at the MDI

(Medium Dependent Interface) that is Jtxout - apply a 5 kHz high-pass filter to the TX_TCLK jitter, measure the

peak-to-peak remaining jitter, and add Jtxout, the result must be less than 0.3 ns. Also, the result of measuring

the peak-to-peak jitter on the TX_TCLK relative to an un-jittered reference must be less than 1.4 ns.

We can assume the Jtxout is small. So, it proposes the following measurements when TX_TCLK is unavailable:

the unfiltered peak-to-peak jitter at the MDI and the peak-to-peak remaining jitter when the unfiltered jitter is

filtered by a 5 kHz high-pass filter.

Since unfiltered jitter measured at the MDI is the sum of TX_TCLK jitter, plus Jtxout, if the result is less than

1.4 ns peak-to-peak then we can be sure that the TX_TCLK jitter is also less than 1.4 ns – in this case we can say

that this measurement “passes.” Keep in mind, this test is more difficult to pass than the test of unfiltered jitter on

TX_TCLK test specified in IEEE 802.3-2005 because the signal on the MDI includes Jtxout. It is not possible to

say with certainty that the DUT should fail this test if the result is more than 1.4ns because it is not possible to

know how much of the measured jitter was Jtxout.

Appendix 40.B-1 (Page 43 of the Gigabit Ethernet Consortium, Clause 40, PMA Version 2,.4:16, June 2006) also

measures the signal at the MDI to approximate the filtered jitter on the TX_TCLK test because the signal on the

MDI is the only signal available.

In the filtered master jitter test in IEEE 802.3-2005 Jtxout is not filtered. The peak-to-peak value of Jtxout

(remember, that is the jitter between TX_TCLK and the signal at the MDI) is added to the filtered TX_TCLK jitter.

In this test, the signal on the MDI (with the TX_TCLK jitter plus Jtxout) is high-pass filtered. Therefore, this test is

easier to pass than the test in 802.3 (because Jtxout is filtered). So, if a device produces a value greater than

0.3 ns, we can say with certainty that it has failed the filtered TX_TCLK test. However, it is not possible to say with

certainty that a DUT passed this test if the filtered jitter at the MDI is less than 0.3 ns. This (like 802.3) is also

because it is not possible to know how much of the measured jitter was due to Jtxout.

So, the larger the contribution from Jtxout, the more this test underestimates the filtered jitter test result, since the

standard test would add the peak-to-peak unfiltered Jtxout to the filtered TX_TCLK peak-to-peak jitter. Appendix

40.B-1 summarizes this in the following

Table 8

Parameter Conformance Limit Result < Limit Result > Limit

Unfiltered TM2 jitter

1.4 ns PASS Inconclusive

Filtered TM2 jitter

0.3 ns Inconclusive FAIL

Table 8. Jitter Test Mode Limits

Perform the test by doing the following:

1. Make the DUT generate the Test Mode 2 signal.

2. Connect the MDI of the DUT to J64 of the TF-ENET text fixture.

3. Connect oscilloscope channel 2 and channel 3 as described in

Table 9. Jumper configuration for each

pair measurements

(as follows) to test a given pair (A, B, C, D). See

Figure 45

for an example

connection diagram.

4. On the oscilloscope menu, select Analysis Ethernet tests. Set up the test and press the Set Up and

Start Test button. Both filtered and unfiltered measurements are made on the same data.

1 2 ... 52 53 54 55 56 57 58 59 60 61 62 ... 77 78

Commentaires sur ces manuels

Pas de commentaire

Teledyne-lecroy QPHY-ENET Manuel d'utilisateur Page 57

Commentaires sur ces manuels

Produits connexes et manuels pour Logiciel Teledyne-lecroy QPHY-ENET