Tektronix 071-0590-00 user manual Prbs Generation Circuits a few sample diagrams, Doutput

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PRBS Generation Circuits - A few sample diagrams

PRBS generators are named after the number of combinations they generate; thus the 28-1 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:

XOR

D Q1 D Q2 D Q3

CLK

Output

Figure B-1. Three-stage PRBS generator (23-1 PRBS)

Note: Make sure shift registers are not initialized to logical 0’s - this is an illegal state.

XOR

A B

D Q1 D Q2 D Q3 D Q4

C

CLK

Doutput

Figure B-2. Four-stage PRBS generator (24-1 PRBS)

GB1400 User Manual B-5