In this case your attempting to average out the LSB. Note that this is only
an advantage as the noise is nominaly equivalent to the LSB. While on this
matter we must also consider the noise source. In an ADC the noise generated
is ((1/root 12) * the LSB) (Noise typically has peeks 6 to 8 times the
average!) so this is the base noise floor of the ADC (General term). From
this we can see if the noise on the signal is greater than or less than
(Remember that noise is adative not subtractive)
Back to the original LSB stuff.
What we are attempting to do is to find the LSB value. Note that the ADC
qunatizes the sample so that it is to the next lowest LSB value. Thus if tou
are .1LSB lower then the result will be 0.1LSB less, however normal rounding
would consider this as 1LSB more!



Dennis




> -----Original Message-----
> From: James Newton [SMTP:jamesnewton@PICLIST.COM]
> Sent: Thursday, 4 May 2000 2:34
> To:   PICLIST@MITVMA.MIT.EDU
> Subject:      Re: [OT] [EE] 24-bit A/D. Are We in the Twilite Zone Here?
>
> I don't understand "duplicate numbers slide off the top of one another".
>
> I also can't see how this jittering could have any positive effect. I
> could
> understand shifting it one bit left and then average with previous
> readings... The random extra bit makes the reading #.5 rather than #.0. Is
> that what we are talking about?
>
> ---
> James Newton (PICList Admin #3)
> mailto:jamesnewton@piclist.com 1-619-652-0593
> PIC/PICList FAQ: http://www.piclist.com or .org
>
> -----Original Message-----
> From: pic microcontroller discussion list
> [mailto:PICLIST@MITVMA.MIT.EDU]On Behalf Of Alice Campbell
> Sent: Wednesday, May 03, 2000 01:08
> To: PICLIST@MITVMA.MIT.EDU
> Subject: Re: [OT] [EE] 24-bit A/D. Are We in the Twilite Zone Here?
>
>
> Dan:
> Think of it as the opposite of averaging data. to average,
> shift right and get twice the number of samples.  To jitter,
> shift left one space and add 1 bit randomly + or - to each
> one.  Suddenly duplicate numbers slide off the top of one
> another.  Particularly useful for plotting data or making
> sounds,the blurry data is actually more usable than the
> original.
>
> alice
>
>
> > At 03:24 AM 4/29/00 -0700,  Tom Handley wrote:
> > ........
> > >PSBS: I had more to say on the LTC2400 and Dennis' comments about
> > >`Think before you comment' and "Bit Jittering" which I assume meant
> > >"Dithering" which I don't think is practical at the sub uV level but
> > >I've been busy and I'll try to follow up...
> > >
> >
> > Tom,
> >
> > I've been itching to hear your comments on signal "jittering/dithering".
> >
> > Andy Kunz mentioned in passing that he uses this technique, but did
> > not elaborate on how it was done or what kind of improvement he saw.
> >
> > best regards,
> > - Dan Michaels
> > ==============