[hpsdr] 24 bit Sigma -Delta ADCs from AD

[Robert W McGwier]

Let us suppose we put a single tone in 1.25 MHz or 2.5 MHz if you are 
using a pair in quadrature.

You can get close to 100 dB SNR in that full bandwidth if we believe the 
specifications.

Now filter and downsample that to 2500 Hz (say) which contains the 
tone.   The noise  will be reduced by a factor of  1000 BY FILTERING THE 
NOISE OFF THAT IS OUT OF BAND  through a filtering and decimation 
process that saves ticks and gets rid of the useless junk. 

That factor of 1000 is a fairly large number of dB of theoretical 
processing gain and that translates directly to SNR.

All of these numbers are theoretical numbers, based on flat amplitude 
responses, etc.  but the prinicipal does hold in practice.

Bob
N4HY



Chuck Hutton wrote:
> ***** High Performance Software Defined Radio Discussion List *****
>
> The 7760 looked great (including the FIR) until I saw that the specs are not
> very much better than a 16 bit part when you push the sampling rate out of
> the bottom end. The 100 dB SINR at higher sampling rates is nice but I was
> hoping for a little better. Or maybe I'm being a little tough on the 7760 -
> I was hoping it would digitize the entire MW band.
>
> Chuck
>
> Date: Tue, 9 May 2006 11:42:08 -0400
> From: "Philip Covington" <p.covington at gmail.com>
> Subject: [hpsdr] 24 bit Sigma -Delta ADCs from AD
> To: "HPSDR List" <hpsdr at hpsdr.org>
> Message-ID:
> 	<32aa05ee0605090842h2d8a1a69j7d6e2b1986a46d32 at mail.gmail.com>
> Content-Type: text/plain; charset=ISO-8859-1; format=flowed
>
> Looks like some interesting chips to play with:
>
> <http://www.analog.com/en/prod/0%2C2877%2CAD7760%2C00.html>
>
> <http://www.analog.com/en/prod/0%2C2877%2CAD7762%2C00.html>
>
> <http://www.analog.com/en/prod/0%2C2877%2CAD7763%2C00.html>
>
> The user programmable FIR filter with bypass mode is interesting.
>
> 73 de Phil N8VB
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>   


-- 
Robert W. McGwier, Ph.D.
Center for Communications Research
805 Bunn Drive
Princeton, NJ 08540
(609)-924-4600
(sig required by employer)



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