[sdiy] PRN Noise Gennie Question

[Magnus Danielson]

From: Tim Ressel <madhun2001 at yahoo.com>
Subject: [sdiy] PRN Noise Gennie Question
Date: Mon, 28 Mar 2005 11:54:09 -0800 (PST)
Message-ID: <20050328195410.22409.qmail at web54607.mail.yahoo.com>

> Hey all,

Hi Tim!

> I was wondering about a few details when implimenting
> a digital PRN noise source:
> 
> First is sample rate, if that is the right term. At
> what rate do the new samples get generated? 

The technical term is rather chip-rate, which is the clock rate you use to
advance the flip-flops with.

> Second is the output. Do I just use 1 digital line and
> filter it, or should I make a little R2R ladder and
> use many lines?

You can go both ways, but you can use one output and lowpass filter that to get
a more multi-level output. You can also use weigthed resistors to acheive
something similar. The lowpass filter method is fairly simple thought.

Keep the lowpass filter cut-off beyond your expected highest frequency.
Keep the chip-rate some suitable multiple beyond your cut-off frequency, I'd
say 10-15 times at least.
Keep the sequence length long enought so that it is dense enought for your
lowest frequency and avoid beating.

Cheers,
Magnus