Topband: Analog to Digital converter for 1.8MHz

[CHARLES HUTTON]

Right you are - neither the A/D's S/N nor the SFDR will tell you the actual 
dynamic range. The real number is - as you say - limited to 6 dB per bit 
given no other factors such as gain control in front of the A/D or other 
sources of non-linearity and noise.


Chuck



>From: Bill Tippett <btippett at alum.mit.edu>
>To: topband at contesting.com
>Subject: Topband: Analog to Digital converter for 1.8MHz
>Date: Fri, 02 Jul 2004 15:14:44 -0400
>
>Chuck wrote:
>
> >The 71.5 dB is actually S/N, not dynamic range. The Spurious Free Dynamic
>Range (SFDR) is listed in the spec sheet as 90 dB which is respectable if
>not top of the line.
>
>         I believe we're mixing apples and oranges.  12-bit ADC resolution 
>is
>1 part in 4096 (2^12).  This yields 20 log (1/4096) = 72.25 dB theoretical
>maximum dynamic range, without any non-linearities elsewhere and without
>any auto-ranging attenuators (Rhode & Schwarz technique).  A DSP cannot
>create any better dynamic range than the ADC feeding it.  Somewhere Icom
>touted their 24-bit DSP as having 144 dB dynamic range (...true in theory),
>but in fact both the Pro2 and 7800 both have close-spaced IMD dynamic range
>numbers in the 70's.  I recall someone at Ten-Tec saying the dynamic range
>of Orion's DSP (which also uses a 24-bit ADC) is in the order of 105 dB
>due to system non-linearities, etc, and yet Orion's close-spaced IMD
>measures in the mid-90's.
>
>         By the way, has anyone seen measurements of the IC-7800's claimed
>"110 dB dynamic range" published anywhere?  I have a feeling this is more
>marketing hype from Icom...never to be measured anywhere except in their
>advertising copywriter's office.  ;-)
>
>                                                 73,  Bill  W4ZV
>
>
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