Filter
Top Products
BERT Primer
GB1400 User Manual B-5
PRBS Generation Circuits - A few sample diagrams
PRBS generators are named after the number of combinations they generate; thus
the 2
8
-1 PRBS is generated from 255 unique 8-bit combinations, each producing
one bit in the output stream. The all-zero state is excluded (accounting for the -1),
because it would generate itself and no other combination. Additionally, the
occasional 1 is required to keep a line alive, so an all-zero pattern beyond a
specific bit length should never occur in real traffic. Sample PRBS generators
are shown below:
D Q1 D Q2 D Q3
CLK
Output
XOR
Figure B-1. Three-stage PRBS generator (2
3
-1 PRBS)
Note: Make sure shift registers are not initialized to logical 0’s - this is an
illegal state.
D
Q3
D
Q4
CLK
output
D
Q2
D
Q1
XOR
A B
C
D
Figure B-2. Four-stage PRBS generator (2
4
-1 PRBS)