Hello,

           I am using Linear feedback shift register(LFSR) to test Digital
filter(DF) because LFSR generate white noise and has a flat like spectrum.
Can anynody suggest when I pass white noise in DF, on what citeria should I
judge the filter (Device Under Test) is pass or fail ?? my filter is 3rd
order polyphase comb decimation filter with decimation factor of 256.

                   I will appreciate if somebody pass hints or forword
suggestions.

Thanks in advance.

Abdul

Abdul wrote:
> Hello,
> 
>            I am using Linear feedback shift register(LFSR) to test Digital
> filter(DF) because LFSR generate white noise and has a flat like spectrum.
> Can anynody suggest when I pass white noise in DF, on what citeria should I
> judge the filter (Device Under Test) is pass or fail ?? my filter is 3rd
> order polyphase comb decimation filter with decimation factor of 256.
> 
>                    I will appreciate if somebody pass hints or forword
> suggestions.
> 
That depends entirely on what your filter is supposed to do.  Generally 
when you design something you start by clarifying what it is you want, 
then you go from there to a design, then you check that you design meets 
prediction by testing.

So predict what your desired filter's output would be when using input 
from the LFSR, and check to see if your actual filter matches.

-- 

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

"Abdul" <abdul_araheem@yahoo.com> wrote in message
news:cucnlu$ha4$1@rzsun03.rrz.uni-hamburg.de...
> Hello,
>
>            I am using Linear feedback shift register(LFSR) to test Digital
> filter(DF) because LFSR generate white noise and has a flat like spectrum.
> Can anynody suggest when I pass white noise in DF, on what citeria should
I
> judge the filter (Device Under Test) is pass or fail ?? my filter is 3rd
> order polyphase comb decimation filter with decimation factor of 256.

If you designed the filter (using certain specs I'm sure) then you should
know exactly what to test for (hint - the specs).
The pass/fail criteria should really come from the designer of the filter -
there isn't a universal rule. So for example, you might be looking for 3dB
BW, stop band attenuation, transition BW, passband ripple etc. It's likely
that you don't care about some of these params and that's ok - but it's for
you to decide/know.

Cheers
Bhaskar

>
>                    I will appreciate if somebody pass hints or forword
> suggestions.
>
> Thanks in advance.
>
> Abdul
>
>