Agilent Technologies N4962A Uživatelská příručka stáhnout pdf (Strana 8)

BER Tester with Agilent N4982A Clock Recovery Unit

The N4962A serial BERT 12.5 Gb/s can also be used with a broadband clock

recovery unit, like the low-cost Agilent N4982A clock recovery unit. This

“AnyRate” CRU will recover a clock from a PRBS bit stream from 622 Mb/s to

13.5 Gb/s—perfect for use with the wide operating range of the Agilent BERT.

By recovering the clock from the DUT output, the BERT can accommodate

tests where polarization mode dispersion (or other physical effects) can

change the period of the data. This is illustrated in Figure 9.

N4982A CRU

LF TrigO

HF TrigO

JitterI

EXT CKI

TX CKO

~IN

~OUT

OUT

Splitter

Out

DUT with PMD

RX CKI

RX CKO

TX CKI

N4962A serial BERT

12.5 Gb/s

CLK output

~CLK output

Data input

E/O

O/E

Figure 9. Block diagram – BER measurement with Agilent clock recovery unit

A passive power splitter is required to duplicate the output signal of the DUT to

feed the BERT and CRU input. If the output from the DUT is severely degraded

or very low in amplitude, a buffer or retiming stage may be required to boost the

amplitude to meet the sensitivity of the BERT and CRU.

If the DUT has a differential output, one side should be delivered to the BERT

IN, and the other side should be connected to the CRU input. This will eliminate

the power splitter from the block diagram, and will allow operation at lower DUT

output levels. This is shown in Figure 10.

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Agilent Technologies N4962A Uživatelská příručka Strana 8