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    site:edaboard.com prbs pattern

    what is the use of PRBS patterns?

    anyone can explain to me what is prbs pattern? why is it used in testing a transmitters functionality?

    anyone got any notes regarding this?

    •   Alt3rd April 2007, 01:46

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    Re: why do we use PRBS pattern?

    well from your previous posts, you mentioned you were testing an optical transmitter (tx).

    PRBS pattern is a sequence of random bits of 1 and 0.
    It is used as test pattern because it can be used as a worst case test pattern. Using sequential bit 1 and 0 will not be a worst case test pattern.

    It is always better to test a tx with the worst signal to check if we can retrieve the worst signal at the receiver(rx). A tx that can transfer a noisy signal accurately to the rx definately can transfer a good signal without any problem.

    therefore, we use PRBS as the test pattern.

    To test your optical tx, you need to input a PRBS (ex: PRBS 2^23-1 at 1.25Gbps optical signal maybe at wavelength 850nm) to your evaluation board. The PRBS is generated by a Pulse Pattern Generator. You need to connect your PPG to a VCSEL source and adjust the extinction ratio and average optical power to the desired value. The light source will be connected to the bare die(via evaluation board) through a TOSA or laser diode. You can observe the eye diagram of the optical signal transmitter in a Sampling Osciloscope. Then you can valdiate the tx design whether the eye follows simulation using Cadence Spectre or other tools.



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    Re: why do we use PRBS pattern?

    u have bombarded me with a lot of info. thanks.

    but seriously i dont understand half of wat you are trying to say. can you pass me an example of a test plan for an optical transmitter?



    •   Alt3rd April 2007, 06:27

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    Re: why do we use PRBS pattern?

    well.. i have given to you in the previous post on stuff to read about. it takes time to learn. be patient n consistent.

    i cant pass you any evaluation plan cause its against the company's regulations.
    try taking a look at maxim's website, agilents website and textronic website. u might get some info there



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    why do we use PRBS pattern?

    PRBS -Pseudorandom bit sequence is just a "highly random" sequence with completely no correlation with adjacent bits... It may be considered equivalent to "noise" since the autocorrelation is a Kronecker delta function...

    If i have an n-bit LFSR, with an initial state being one out of 2^n - 1 states except "all zero sate", i can maximally generate a PRBS by modifying the taps of the LFSR... The PRBS sequence repeats after all states have completed, hence it is "pseudo-random"... This is the fundamental behind the generation of CA codes or gold codes, use din CDMA and GPS systems...


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    why do we use PRBS pattern?

    How do you check that the PRBS data was received correctly? i.e. what is the algorithm used for the signature analyzer?



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    Re: why do we use PRBS pattern?

    Quote Originally Posted by sparso
    How do you check that the PRBS data was received correctly? i.e. what is the algorithm used for the signature analyzer?
    I think when we test an E1 by PRBS, we need a loopback device to forward signal back. After comparing, we can estimate the error bit.



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