User guide

7
BER Tester with Jitter Injection for Stressed Eye Testing
The N4962A serial BERT 12.5 Gb/s also has the capability to inject jitter
onto the output PRBS datastream; an important component of IEEE-specified
stressed eye tests. This is accomplished by applying an external signal to the
JitterI input port as illustrated in Figure 8.
Oscilloscope
LF TrigO
HF TrigO
JitterI
EXT CKI
TX CKO
IN
~IN
~OUT
OUT
DUT
Function
generator
RX CKI
RX CKO
TX CKI
N4962A serial BERT
12.5 Gb/s
Precision
trigger
input
Data
input
Figure 8. Block diagram – BER measurement with jitter injection for stressed eye testing
The function generator generates the signal that the BERT FM modulates onto
the full-rate clock. This is typically a sinusoid, but the JitterI input could be
a square wave, a Gaussian noise source, and even an uncorrelated PRBS bit
stream.
The JitterI input bandwidth is DC to 100 MHz; the N4962A serial BERT
12.5 Gb/s User Guide spells out the amount of UI that can be injected in
Section 2.2. The UI injection vector is also supplied, relating the input voltage
to UI of jitter injected.
The jitter is applied to the TX CKO and HF TrigO outputs. The RX CKO and LF
TrigO outputs are not jittered. The JitterI input requirements range from 0 to 2 V.
Consult the BERT User Guide for detailed procedures regarding the use of the
jitter injection feature: change the jitter option to 1.