# PN sequence for ADC & DDC ?

I am working with the AD6636 (DDC) and AD9251 (ADC) , both of which have a PN sequence generator, usually used for BIST purposes.

I am interested in vaildating my raw data streams from these devices when they are outputting the PN streams,

Can anyone tell me

1. the algorithm that generates these data... are they LFSR based?

2. Any post-PN generation data changes that might be occuring**

.. such that I can recreate the raw device output?

For AD9251 option, there are 2 possible generators: PN9 & PN23.

**For PN9, I notice ALL 14 bits seem to be changing, which means there is not a direct relationship between the PN generator state and the output.

Also, PN9 seqeunce period seems to be significantly less than the expected 511 samples.

Thanks for any replies.

David.

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