D1-01_PRBS generation.pdf - PRBS GENERATION PREPARATION.2 digital messages.2 random binary sequences.2 viewing 3 applications.4 bit clock acquisition 4

D1-01_PRBS generation.pdf - PRBS GENERATION PREPARATION.2...

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Copyright © 2005 Emona Instruments Pty Ltd D1-01-rev 2.0 - 1 PRBS GENERATION PRBS GENERATION PRBS GENERATION PREPARATION ................................................................................ 2 digital messages ......................................................................... 2 random binary sequences ........................................................... 2 viewing .................................................................................................. 3 applications ............................................................................... 4 bit clock acquisition ............................................................................... 4 EXPERIMENT .................................................................................. 4 the ‘snapshot’ display ................................................................ 4 band limiting .............................................................................. 6 two generator alignment ............................................................ 7 two sequence alignment ............................................................. 9 the sliding window correlator ................................................................. 9 the model ............................................................................................. 10 TUTORIAL QUESTIONS ............................................................... 11 APPENDIX ...................................................................................... 12 PRBS generator - sequence length ........................................... 12 error counting utilities - X - OR .................................................. 12
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D1-01 - 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 signal-to-noise 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.
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PRBS generation Copyright © 2005 Emona Instruments Pty Ltd D1-01 - 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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