Copyright © 2005 Emona Instruments Pty Ltd
D101rev 2.0  1
PRBS GENERATION
PRBS GENERATION
PRBS GENERATION
PREPARATION
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2
digital messages
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2
random binary sequences
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2
viewing
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3
applications
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4
bit clock acquisition
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4
EXPERIMENT
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4
the ‘snapshot’ display
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4
band limiting
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6
two generator alignment
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7
two sequence alignment
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9
the sliding window correlator
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9
the model
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10
TUTORIAL QUESTIONS
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11
APPENDIX
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12
PRBS generator  sequence length
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12
error counting utilities 
X

OR
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12
D101  2
Copyright © 2005 Emona Instruments Pty Ltd
PRBS GENERATION
PRBS GENERATION
PRBS GENERATION
ACHIEVEMENTS
:
introduction to the pseudo random binary sequence (PRBS)
generator;
time domain viewing:
snap shot and eye patterns;
two
generator synchronization and alignment with the ‘sliding window
correlator’
PREREQUISITES:
none
EXTRA MODULES:
a second SEQUENCE GENERATOR,
ERROR
COUNTING UTILITIES.
PREPARATI
PREPARATI
PREPARATION
ON
ON
digital messages
digital messages
In analog work the standard test message is the sine wave, followed by the two
tone signal
1
for more rigorous tests.
The property being optimized is generally
signaltonoise ratio (SNR).
Speech is interesting, but does not lend itself easily
to mathematical analysis, or measurement.
In digital work a binary sequence, with a known pattern of ‘1’ and ‘0’, is
common.
It is more common to measure bit error rates (BER) than SNR, and
this is simplified by the fact that known binary sequences are easy to generate
and reproduce.
A common sequence is the pseudo random binary sequence.
random binary sequences
random binary sequences
The output from a pseudo random binary sequence generator is a bit stream of
binary pulses;
ie., a sequence of 1`s (
HI
) or 0`s (
LO
), of a
known
and
reproducible
pattern.
The bit
rate
, or number of bits per second, is determined by the frequency of an
external
clock
, which is used to drive the generator.
For each clock period a
1
see the experiment entitled
Amplifier overload
in Volume A2.
PRBS generation
Copyright © 2005 Emona Instruments Pty Ltd
D101  3
single bit is emitted from the generator; either at the ‘1’ or ‘0’ level, and of a
width equal to the clock period.
For this reason the external clock is referred to
as a
bit clock
.
For a long sequence the 1`s and 0`s are distributed in a (pseudo) random manner.
The sequence pattern
repeats
after a defined number of clock periods.
In a
typical generator the
length
of the sequence may be set to 2
n
clock periods, where
n is an integer. In the TIMS SEQUENCE GENERATOR (which provides two,
independent sequences, X and Y) the value of n may be switched to one of three
values, namely 2, 5, or 11.
There are
two
switch positions for the case n = 5,
giving different patterns.
The
SYNCH
output provides a reference pulse generated
once per sequence repetition period.
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