Hi guys, It is a known fact that LFSR generate flat spectrum, I choosed LFSR to test my 3rd order polyphase comb decimation filter with decimation factor of 256. I am wondering what would be the lenght of LFSR ? it should be 4 bit or 8 bit or 10 bit ?? All generate flat spectrum. What characteristics help me in choosing the lenght of LFSR ??. I have read few technical papers, In which LFSR is being used in Build In Self Test(BIST) to test Sigma delta modulator and no where specified the lenght of LFSR. I have one idea to select lenght. 1) Its depends on the how many pattern we would like to generate for example 8 bit LFSR gives 2^8 -1 and 10 bit generate 2^10-1. More pattern would give us better results. 2) The sequence should be longer than the delay response of filter. I am wondering whether this two points would justify in choosing the lenght of LFSR. if I can reduce lengh of LFSR by a factor of one would help in reducing the area and power on ASIC chip. It would be nice if you guys forward some hints or ideas to choose the lenght of LFSR. warm regards, Abdul
Digital Filter testing with LFSR
Started by ●January 26, 2005
Reply by ●January 26, 20052005-01-26
"Abdul" <abdul_araheem@yahoo.com> wrote in message news:ct85c8$454$1@rzsun03.rrz.uni-hamburg.de...> Hi guys, > > It is a known fact that LFSR generateflat spectrum, I> choosed LFSR to test my 3rd order polyphase combdecimation filter with> decimation factor of 256. I am wondering what would be thelenght of LFSR ?> it should be 4 bit or 8 bit or 10 bit ?? All generate flatspectrum. What> characteristics help me in choosing the lenght of LFSR ??. > > I have read few technical papers, In which LFSR is beingused in Build In> Self Test(BIST) to test Sigma delta modulator and no wherespecified the> lenght of LFSR.First of all, you probably want at least 31 bits unless you really don't care about the periodicity introduced by the LFSR. Configurations with taps at (31,3,0), (31,6,0), and (31,13,0) will produce maximal periods. Second, the output of a simple LFSR is highly predictable using the Massey Berlekamp algorithm. If you must to use an LFSR, I suggest you use a configuration like the Bilateral Stop-and-Go generator, or something similar.> > I have one idea to select lenght. > > 1) Its depends on the how many pattern we would like togenerate for> example 8 bit LFSR gives 2^8 -1 and 10 bit generate2^10-1. More pattern> would give us better results. > > 2) The sequence should be longer than the delay responseof filter.> > I am wondering whether this two points would justify inchoosing the lenght> of LFSR. if I can reduce lengh of LFSR by a factor of onewould help in> reducing the area and power on ASIC chip. > > It would be nice if you guys forward some hints or ideasto choose the> lenght of LFSR. > > warm regards, > > Abdul > >