Re: Basic info needed regarding filters (FIR)

John Larkin wrote:
On Thu, 22 Nov 2007 05:20:12 -0800 (PST), "faizankhan666@xxxxxxxxx"
<faizankhan666@xxxxxxxxx> wrote:

I am very new with the subject of Digital logic design and Our teacher
has given us a project of "Implementation of FIR filters" .We have to
use Verilog also.
I just know the clk,reset,set,flip flops designs....

I just want to know what filter is used for and also
Please tell me What do we mean by 4 tap filters.
What does FIR do?

Google "fir filter."

Quickie starter dose:

A signal, like a sound, can be expressed as a series of samples, each
an n-bit integer. CD music is stored this way.

A filter changes the math. A lowpass filter reduces high frequencies,
cuts the treble. If you have a stream of samples coming in, you can
store the last N of them in a list and process the list to do all
sorts of filtering.

A Finite Impulse Response (FIR) filter takes the list of recent
samples, multiplies each one by some individual factor, and sums them
to make the output.

"Finite" because if you kick it with an impulse (one lone non-zero sample in a long string of zero samples) the output only lasts for a finite period of time.

Contrast this to the Infinite Impulse Response (IIR) filter which has feedback, and whose response to an impulse is, theoretically at least, infinitely long.

Filter_output =

(Latest sample * Factor1) +
(1st oldest sample * Factor2) +
(2st oldest sample * Factor3) +

etc, as far as you want to go.

One simple lowpass filter is a boxcar integrator, where all the
factors are 1. The output is just the sum (or average, if you prefer)
of the last N samples.

OK, google+wikipedia will get you the gory details. Good luck.

Coffee's ready.

John



--

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

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" gives you just what it says.
See details at http://www.wescottdesign.com/actfes/actfes.html
.

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