Agilent Technologies N4962A Podręcznik Użytkownika Pobierz pdf (Strona 51)

Operation

Serial BERT 12.5 Gb/s User Guide 51

4.5.4 Low BER Test

To verify that the error detector can correctly count a small number of errors,

use the PRBS error injection capability to insert a known number of errors into

the bit stream, as follows:

• Put the system in self test mode, described in Section 4.5.1.

• Press the Display > Scroll ↓ button and select ErAd OFF

• Press the Adjust > Config State + button and select ErAd 1E0

• Press the Receiver > On button and ensure the light is on

• Observe the Error ε light (should blink once per second)

• Press the Display > Scroll ↑ button and select Err (should show 1 per

second)

• Press the Display > Scroll ↓ button and select BER (should show

1E-10)

• Press the Display > Scroll ↓ button and select ε time (sec) (should be

increasing)

4.6 BER Detector Clock Phase Adjustment

The error detector clock phase can be electronically controlled to adjust the

detector sampling point; the periodic point at which the detector interprets the

incoming bit stream. Due to the unknown delay associated with cables and the

DUT in the data path, the incoming bit stream may not be sampled at the

optimal point.

The detector must be adjusted to find the optimal sampling point; an incorrect

sampling point will yield an artificially-high BER measurement, shown in Figure

14.

Figure 14. Sampling uncertainty due to clock phase misadjustment

IN, notIN

RX CKI

good

IN, notIN

RX CKI

uncertain

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Agilent Technologies N4962A Podręcznik Użytkownika Strona 51