[time-nuts] T.I. questions
Mike Monett
timenuts at binsamp.e4ward.com
Sun Feb 8 02:40:35 UTC 2015
>magnus at rubidium.dyndns.org said:
>> The typical noise generator chips uses a PRNG based on DFFs and XOR
>> gate(s). A typical weakness is that the chain of DFFs is to short, causing
>> a relatively high rate of cycling, which hearable as a beating. However, for
>> some uses, that is OK.
>The buzzword for the typical PRNG is LFSR - Linear Feedback Shift Register.
>Many years ago, Xilinx published a good app-note on this topic.
Several, in fact. I spent some time tracking them down. Here's the previous
list:
xapp210
xapp211
xapp217
xapp220
But I found one more - XAPP052. It has a feedback table from N=3 to 168.
The table is repeated in later app notes. Also, Xilinx has apparently lost
XAPP217. It no longer appears on their web site, but I found it. Here's the
updated list:
XAPP052 LFSR Generators N=3 to 168
http://www.xilinx.com/support/documentation/application_notes/xapp052.pdf
XAPP210 LFSR in Vertix Devices
http://www.xilinx.com/support/documentation/application_notes/xapp210.pdf
XAPP211 PDF PN Generators Using The SRL Macro
http://www.xilinx.com/support/documentation/application_notes/xapp211.pdf
XAPP217 Gold Code Generators
77-42925.pdf http://application-notes.digchip.com/077/77-42925.pdf
XAPP220 LFSRs As Functional Blocks in Wireless Applications
http://uglyduck.ath.cx/PDF/Xilinx/Spartan3/appnotes/xapp220.pdf
Mike Monett
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