Specifications
B-3
Appendix B
Pattern Generation
clock-to-data alignment. To select a new eye edge threshold press the
hardkey then select and enter a new eye edge threshold using the
numeric keypad.
NOTE On RAM based (USER) patterns the error detector may gain sync at a
point in the pattern where the criteria for synchronization (set by the
Sync Threshold) is met; but is not the correct point where the internally
generated reference pattern and the data input pattern match. When the
error detector gains sync incorrectly errors occur and clock-to-data
alignment may fail. If this occurs reset the eye edge threshold to a
lower value and recheck the error rate and clock-to-data alignment.
NOTE For most RAM based patterns synchronization should occur in less
than 3 seconds. However synchronization times are dependent on
pattern length, pattern content and clock frequency and will increase as
pattern length increases or clock frequency decreases. For very long
patterns (for example 8 Mb/s) times could be of a minute or more.
Pattern Generation
Introduction
• Patterns in the Agilent 71612 pattern generator or error detector are generated either
from hardware registers or from patterns stored in random access memory (RAM).
• PRBS patterns 2
7
-1, 2
10
-1, 2
15
-1, 2
23
-1, 2
31
-1 are generated from hardware registers.
Patterns are generated 32-wide and so a trigger output is produced once for every 32
repetitions of the serial pattern.
• All other patterns are generated from RAM.
The RAM in the instrument is 256 bits wide, this controls how patterns are stored and in
turn how some features work.
Within the instrument, patterns are replicated in RAM until they fit an exact multiple of
256 bits. Patterns which are already a multiple of 256 bits need no replication, other
patterns are replicated as many as 256 times. For example, all odd-length patterns are
replicated 256 times. The replication controls the way a number of instrument features
operate.
•Triggerrate
• Pattern granularity
• Bit and block BER measurement sampling rate
sync & audio
EYE EDG THRSHLD