Maximum useable oversampling rate10x analog signal bandwidth?

Analog Devices comments on their web site that for oversampling to work
the sample rate cannot be over 10 times the analog signal bandwidth. So
this defines the upper bounds on how much you can reduce the noise
floor of an analog signal. So I am thinking what magical about 10x, but
I suppose they are implying that if you had a 100hz bandwidth limited
signal and oversampled it 1024 times at 1Ghz rate all the samples would
be the same value anyway since if the signal is truly bandlimited at
100Hz it couldn't change quick enough to be different between samples.
So whats the question? Well I guess I actually answered it as I am
writing this post, funny how writing the question down does that!

Thinking about it some more I suppose oversampling rates greater then
10x the signal bandwidth could help to reduce internal a/d noise, clock
noise, switching power supply noise and any other high frequency noise
that sneaks in after the external analog filter or though an external
a/d voltage reference.

steve wrote:
> Analog Devices comments on their web site that for oversampling to work
> the sample rate cannot be over 10 times the analog signal bandwidth. So
> this defines the upper bounds on how much you can reduce the noise
> floor of an analog signal. So I am thinking what magical about 10x, but
> I suppose they are implying that if you had a 100hz bandwidth limited
> signal and oversampled it 1024 times at 1Ghz rate all the samples would
> be the same value anyway since if the signal is truly bandlimited at
> 100Hz it couldn't change quick enough to be different between samples.
> So whats the question? Well I guess I actually answered it as I am
> writing this post, funny how writing the question down does that!
> 
> Thinking about it some more I suppose oversampling rates greater then
> 10x the signal bandwidth could help to reduce internal a/d noise, clock
> noise, switching power supply noise and any other high frequency noise
> that sneaks in after the external analog filter or though an external
> a/d voltage reference.

If they really said that more than 10x won't work, then your explanation
doesn't either, but I doubt that they say it. If they say that more than
10x is pointless, I guess that's true. The signal is contaminated by any
noise produced by the sampling chain within the signal's band. and any
outside the band can be filtered out regardless of the sample rate. I
don't really understand your question either.

Jerry
-- 
Engineering is the art of making what you want from things you can get.
�����������������������������������������������������������������������

"steve" <bungalow_steve@yahoo.com> wrote in message
news:1106449193.210985.208270@z14g2000cwz.googlegroups.com...
> Analog Devices comments on their web site that for
oversampling to work
> the sample rate cannot be over 10 times the analog signal
bandwidth. So
> this defines the upper bounds on how much you can reduce
the noise
> floor of an analog signal. So I am thinking what magical
about 10x, but
> I suppose they are implying that if you had a 100hz
bandwidth limited
> signal and oversampled it 1024 times at 1Ghz rate all the
samples would
> be the same value anyway since if the signal is truly
bandlimited at
> 100Hz it couldn't change quick enough to be different
between samples.
> So whats the question? Well I guess I actually answered it
as I am
> writing this post, funny how writing the question down
does that!
>
> Thinking about it some more I suppose oversampling rates
greater then
> 10x the signal bandwidth could help to reduce internal a/d
noise, clock
> noise, switching power supply noise and any other high
frequency noise
> that sneaks in after the external analog filter or though
an external
> a/d voltage reference.
>

Once upon a time, I designed a controller to sample at 1200
Hz. even though it was for a system whose natural time
constants were measured in tens of seconds.  The reason was
that I could easily apply a post sampling digital filter
that would reduce 60 Hz and 120 Hz noise picked up from the
environment to levels that were below the quantization
level.  Also, it was a lot easier to implement an
anti-aliasing analog filter for 600 Hz than it would have
been to implement one for 1 Hz.

Jerry Avins wrote:
> steve wrote:
> > Analog Devices comments on their web site that for oversampling to
work
> > the sample rate cannot be over 10 times the analog signal
bandwidth. So
> > this defines the upper bounds on how much you can reduce the noise
> > floor of an analog signal. So I am thinking what magical about 10x,
but
> > I suppose they are implying that if you had a 100hz bandwidth
limited
> > signal and oversampled it 1024 times at 1Ghz rate all the samples
would
> > be the same value anyway since if the signal is truly bandlimited
at
> > 100Hz it couldn't change quick enough to be different between
samples.
> > So whats the question? Well I guess I actually answered it as I am
> > writing this post, funny how writing the question down does that!
> >
> > Thinking about it some more I suppose oversampling rates greater
then
> > 10x the signal bandwidth could help to reduce internal a/d noise,
clock
> > noise, switching power supply noise and any other high frequency
noise
> > that sneaks in after the external analog filter or though an
external
> > a/d voltage reference.
>
> If they really said that more than 10x won't work, then your
explanation
> doesn't either, but I doubt that they say it. If they say that more
than
> 10x is pointless, I guess that's true. The signal is contaminated by
any
> noise produced by the sampling chain within the signal's band. and
any
> outside the band can be filtered out regardless of the sample rate. I
> don't really understand your question either.
>
> Jerry
> --
> Engineering is the art of making what you want from things you can
get.
>
=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=
=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=
=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF
Analog Devices quote from web site
"For oversampling to work, samples need to be taken at a rate no faster
than 10 times the analog bandwidth"

John E. Hadstate wrote:
> "steve" <bungalow_steve@yahoo.com> wrote in message
> news:1106449193.210985.208270@z14g2000cwz.googlegroups.com...
> > Analog Devices comments on their web site that for
> oversampling to work
> > the sample rate cannot be over 10 times the analog signal
> bandwidth. So
> > this defines the upper bounds on how much you can reduce
> the noise
> > floor of an analog signal. So I am thinking what magical
> about 10x, but
> > I suppose they are implying that if you had a 100hz
> bandwidth limited
> > signal and oversampled it 1024 times at 1Ghz rate all the
> samples would
> > be the same value anyway since if the signal is truly
> bandlimited at
> > 100Hz it couldn't change quick enough to be different
> between samples.
> > So whats the question? Well I guess I actually answered it
> as I am
> > writing this post, funny how writing the question down
> does that!
> >
> > Thinking about it some more I suppose oversampling rates
> greater then
> > 10x the signal bandwidth could help to reduce internal a/d
> noise, clock
> > noise, switching power supply noise and any other high
> frequency noise
> > that sneaks in after the external analog filter or though
> an external
> > a/d voltage reference.
> >
>
> Once upon a time, I designed a controller to sample at 1200
> Hz. even though it was for a system whose natural time
> constants were measured in tens of seconds.  The reason was
> that I could easily apply a post sampling digital filter
> that would reduce 60 Hz and 120 Hz noise picked up from the
> environment to levels that were below the quantization
> level.  Also, it was a lot easier to implement an
> anti-aliasing analog filter for 600 Hz than it would have
> been to implement one for 1 Hz.

Yes, very good reasons for oversampling greater then 10x signal BW,
that 1Hz filter would of been huge, thanks for the info.

steve wrote:

  ...

> Analog Devices quote from web site
> "For oversampling to work, samples need to be taken at a rate no faster
> than 10 times the analog bandwidth"

Could you say where that is on the website? The context is crucial.
However high the oversampling ratio, the original signal can be
reconstructed. What does "working" consist of?

Jerry

P.S. I garbled part of my previous message. It should have been (in
part) "The signal is contaminated by any noise produced by the sampling
chain within the signal's band, and any noise outside the band can be
filtered out regardless of the sample rate."
-- 
Engineering is the art of making what you want from things you can get.
�����������������������������������������������������������������������

John E. Hadstate wrote:
> "steve" <bungalow_steve@yahoo.com> wrote in message
> news:1106449193.210985.208270@z14g2000cwz.googlegroups.com...
> > Analog Devices comments on their web site that for
> oversampling to work
> > the sample rate cannot be over 10 times the analog signal
> bandwidth. So
> > this defines the upper bounds on how much you can reduce
> the noise
> > floor of an analog signal. So I am thinking what magical
> about 10x, but
> > I suppose they are implying that if you had a 100hz
> bandwidth limited
> > signal and oversampled it 1024 times at 1Ghz rate all the
> samples would
> > be the same value anyway since if the signal is truly
> bandlimited at
> > 100Hz it couldn't change quick enough to be different
> between samples.
> > So whats the question? Well I guess I actually answered it
> as I am
> > writing this post, funny how writing the question down
> does that!
> >
> > Thinking about it some more I suppose oversampling rates
> greater then
> > 10x the signal bandwidth could help to reduce internal a/d
> noise, clock
> > noise, switching power supply noise and any other high
> frequency noise
> > that sneaks in after the external analog filter or though
> an external
> > a/d voltage reference.
> >
>
> Once upon a time, I designed a controller to sample at 1200
> Hz. even though it was for a system whose natural time
> constants were measured in tens of seconds.  The reason was
> that I could easily apply a post sampling digital filter
> that would reduce 60 Hz and 120 Hz noise picked up from the
> environment to levels that were below the quantization
> level.  Also, it was a lot easier to implement an
> anti-aliasing analog filter for 600 Hz than it would have
> been to implement one for 1 Hz.

Yes, very good reasons for oversampling greater then 10x signal BW,
that 1Hz filter would be huge, thanks for the info.

"Jerry Avins" <jya@ieee.org> wrote in message
news:35gokqF4lh664U1@individual.net...
> steve wrote:
>
>   ...
>
> > Analog Devices quote from web site
> > "For oversampling to work, samples need to be taken at a
rate no faster
> > than 10 times the analog bandwidth"
>
> Could you say where that is on the website? The context is
crucial.
> However high the oversampling ratio, the original signal
can be
> reconstructed. What does "working" consist of?
>

I think the quote from the website is clear (and correct) if
you read it while patting your head and rubbing your tummy
;-)  In other words, you don't have to sample faster than
about 10 times the analog bandwidth for oversampling to be
used effectively.  It does not say that you can't sample
faster; it just says you don't have to sample faster.

Besides being confusingly worded, it's a simplistic
statement.  There may be very good reasons for oversampling
faster than 10x the highest analog frequency.  Consider, for
example, issues involving propagation delays and latencies.

Jerry Avins wrote:
> steve wrote:
>
>   ...
>
> > Analog Devices quote from web site
> > "For oversampling to work, samples need to be taken at a rate no
faster
> > than 10 times the analog bandwidth"
>
> Could you say where that is on the website? The context is crucial.
> However high the oversampling ratio, the original signal can be
> reconstructed. What does "working" consist of?
>
> Jerry
>
> P.S. I garbled part of my previous message. It should have been (in
> part) "The signal is contaminated by any noise produced by the
sampling
> chain within the signal's band, and any noise outside the band can be
> filtered out regardless of the sample rate."
> --
> Engineering is the art of making what you want from things you can
get.
>
=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=
=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=
=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF

see part 8 of

http://www.analog.com/Analog_Root/static/techSupport/designTools/interactiv=
eTools/accelerometer/adxl202.html

Another thing I didn't understand was why the bandwidth is reduced by
oversampling, I thought the whole purpose of oversampling was to
maintained the signal bandwidth at reduced noise at the expense of
faster a/d conversions. I certainly can see if you oversampled but kept
the sampling rate constant you would reduce the bandwidth, but I
wouldn't call that oversampling (and from the online calculator, the
sample rate does increase with increase samples, yet the bandwidth
still drops).

"John E. Hadstate" <jh113355@hotmail.com> wrote in message 
news:V8OId.6180$Gj.1929@bignews3.bellsouth.net...
>
> "Jerry Avins" <jya@ieee.org> wrote in message
> news:35gokqF4lh664U1@individual.net...
>> steve wrote:
>>
>>   ...
>>
>> > Analog Devices quote from web site
>> > "For oversampling to work, samples need to be taken at a
> rate no faster
>> > than 10 times the analog bandwidth"
>>
>> Could you say where that is on the website? The context is
> crucial.
>> However high the oversampling ratio, the original signal
> can be
>> reconstructed. What does "working" consist of?
>>
>
> I think the quote from the website is clear (and correct) if
> you read it while patting your head and rubbing your tummy
> ;-)  In other words, you don't have to sample faster than
> about 10 times the analog bandwidth for oversampling to be
> used effectively.  It does not say that you can't sample
> faster; it just says you don't have to sample faster.
>
> Besides being confusingly worded, it's a simplistic
> statement.  There may be very good reasons for oversampling
> faster than 10x the highest analog frequency.  Consider, for
> example, issues involving propagation delays and latencies.

If you parse the sentence, it seems to say:

fs<=10*B

which is probably not at all what anyone would agree with because values of 
fs like fs=B would be allowed.

or, if you focus on the word "need" then:

min[fs]=10*B

and, the phrase
"need to be taken at a rate no faster than"
is a very awkward way to say:
"you don't need to sample at a rate higher than"
rather than
"you need to sample at a rate not higher than"

It looks like a marketing edit with a misplaced negative...

Fred