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Re: Read this; digital versus analog sensor??

 
 
TheRealSteve
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      02-26-2012

On Sun, 26 Feb 2012 12:28:14 +0100, Mxsmanic <(E-Mail Removed)>
wrote:

>There is no such thing as a digital sensor. All sensors are analog electronic
>devices. More generally, any device that interfaces with the physical world
>will always be an analog device.


Photosensors count the electric charge created by photons incident on
a surface. The energy of a photon is a quantum amount dependent on the
wavelength, which for visible light is the color. Look up Planck's
constant.

Sensitive photosensors can count discrete, non-continuous photon
interactions. There's no "in between" one photon and two photons.
Therefore I wouldn't consider them analog sensors in the strictest
sense of the definition of analog, i.e., continuous.

Steve
 
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TheRealSteve
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      02-27-2012

On Sun, 26 Feb 2012 12:57:52 -0900, http://www.velocityreviews.com/forums/(E-Mail Removed) (Floyd L.
Davidson) wrote:

>TheRealSteve <(E-Mail Removed)> wrote:
>>Sensitive photosensors can count discrete, non-continuous photon
>>interactions. There's no "in between" one photon and two photons.

>
>Maybe such sensors exist, but they are *not* currently being used
>in typical digital cameras such as we discuss in this forum.


Thank you for agreeing that such sensors exist. The point I was
responding to was Msxmanic's assertion:
"There is no such thing as a digital sensor. All sensors are analog
electronic devices. More generally, any device that interfaces with
the physical world will always be an analog device."

That assertion is false.

>>Therefore I wouldn't consider them analog sensors in the strictest
>>sense of the definition of analog, i.e., continuous.

>
>They are though, by definition. 1) They don't count discrete photons.
>2) They output a signal that is clearly analog (continuous) in nature.
>and 3) the signal is *necessarily* digitized by an ADC.


All the ADC is doing is taking an already quantized signal (the
"analog" input signal which really is a quantized output of the
photosensor) and greatly (many orders of magnitude) reducing the
resolution of the steps to something we can conceptually understand
and our computers can make use of.

Steve
 
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TheRealSteve
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      02-27-2012

On Mon, 27 Feb 2012 05:26:10 +0100, Mxsmanic <(E-Mail Removed)>
wrote:

>TheRealSteve writes:
>
>> Photosensors count the electric charge created by photons incident on
>> a surface. The energy of a photon is a quantum amount dependent on the
>> wavelength, which for visible light is the color. Look up Planck's
>> constant.

>
>Yes, but that doesn't make it digital. Digital involves symbols that represent
>information. There is no notion of symbols or information in the physical
>world.


No wonder you're confused. Your definition of "digital" is not
opposite of your definition of "analog" so there's no way you can have
one vs. the other. If analog means continuous then digital means
discrete, or something that can be counted with no in-between steps.
It doesn't necessarily have to mean symbols that represent
information.

According to your definition, if we humans make up symbols that
represent information of an analog nature then the real world cannot
be analog either because the real world doesn't have symbols that
represent information. For instance, if used a picture of a protractor
to represent angles and the pictured protractor could take on any
continuous measured angle value, then the real world cannot be analog.
Doesn't make sense.

>> Sensitive photosensors can count discrete, non-continuous photon
>> interactions. There's no "in between" one photon and two photons.
>> Therefore I wouldn't consider them analog sensors in the strictest
>> sense of the definition of analog, i.e., continuous.

>
>Once these quantums states interact, they blend into something that can no
>longer be recognized as discrete states. Although that doesn't matter, because
>the discrete states of quantum mechanics don't make reality digital, they just
>make it ... discrete.


Wonderful, so you agree the real world is discrete. Sensors that sense
the discrete real world must also exist in the real world, so they are
also discrete. We create discrete sensors can and do output a count of
these discrete real world phenomonon. Sensors that count discrete
things in the real world are digital sensors. So digital sensors can
and do exist.

Steve
 
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Martin Brown
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      02-27-2012
On 27/02/2012 16:17, Floyd L. Davidson wrote:
> TheRealSteve<(E-Mail Removed)> wrote:
>> On Sun, 26 Feb 2012 12:57:52 -0900, (E-Mail Removed) (Floyd L.
>> Davidson) wrote:
>>
>>> TheRealSteve<(E-Mail Removed)> wrote:
>>>> Sensitive photosensors can count discrete, non-continuous photon
>>>> interactions. There's no "in between" one photon and two photons.
>>>
>>> Maybe such sensors exist, but they are *not* currently being used
>>> in typical digital cameras such as we discuss in this forum.

>>
>> Thank you for agreeing that such sensors exist. The point I was
>> responding to was Msxmanic's assertion:
>> "There is no such thing as a digital sensor. All sensors are analog
>> electronic devices. More generally, any device that interfaces with
>> the physical world will always be an analog device."
>>
>> That assertion is false.

>
> Was he talking about camera sensors? I'm not going to go back and
> look it up, as your point is silly on its face.


Not at all. The earliest ultra-sensitive astronomical digital cameras
used a configuration to count and determine the centroid of the flash
caused by individual photons as they hit a channel multiplier plate.

Boksenberg of Imperial College London pioneered the electronics and the
Image Photon Counting technique which was widely used on major
observatory instruments until the thinned CCD technology came along in
the late 1980's. It still has a niche position for some work.

One still seems to be in operation on the ING group of scopes
http://www.ing.iac.es/Astronomy/obse...e/node220.html

--
Regards,
Martin Brown
 
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TheRealSteve
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      02-28-2012

On Mon, 27 Feb 2012 07:17:52 -0900, (E-Mail Removed) (Floyd L.
Davidson) wrote:

>TheRealSteve <(E-Mail Removed)> wrote:
>>On Sun, 26 Feb 2012 12:57:52 -0900, (E-Mail Removed) (Floyd L.
>>Davidson) wrote:
>>
>>>TheRealSteve <(E-Mail Removed)> wrote:
>>>>Sensitive photosensors can count discrete, non-continuous photon
>>>>interactions. There's no "in between" one photon and two photons.
>>>
>>>Maybe such sensors exist, but they are *not* currently being used
>>>in typical digital cameras such as we discuss in this forum.

>>
>>Thank you for agreeing that such sensors exist. The point I was
>>responding to was Msxmanic's assertion:
>>"There is no such thing as a digital sensor. All sensors are analog
>>electronic devices. More generally, any device that interfaces with
>>the physical world will always be an analog device."
>>
>>That assertion is false.

>
>Was he talking about camera sensors? I'm not going to go back and
>look it up, as your point is silly on its face.


Here's what he wrote that started the whole silly discussion:

"There is no such thing as a digital sensor. All sensors are analog
electronic devices. More generally, any device that interfaces with
the physical world will always be an analog device."

But then he went on to say how analog is also a concept and not a
physical reality so there are no analog sensors either. He's fairly
confused.

>>>>Therefore I wouldn't consider them analog sensors in the strictest
>>>>sense of the definition of analog, i.e., continuous.
>>>
>>>They are though, by definition. 1) They don't count discrete photons.
>>>2) They output a signal that is clearly analog (continuous) in nature.
>>>and 3) the signal is *necessarily* digitized by an ADC.

>>
>>All the ADC is doing is taking an already quantized signal (the

>
>The signal has not been quantized prior to the ADC.


The signal is quantized prior to the ADC. It's just that the
quantization steps are approximately 1.602e-19 volts, a very tiny
amount that's so small we can't really comprehend what it means so we
think of it as being continuous. The ADC requantizes that quantized
signal into steps that are, say around 1.5e-5 volts for a linear 16
bit ADC, 1vpp signal. The 14 orders of magnitude greater quantization
steps make it much easier to not only comprehend the fact that the
signal is qauntized but also make it much easier to perform
calculations on.

>>"analog" input signal which really is a quantized output of the
>>photosensor) and greatly (many orders of magnitude) reducing the
>>resolution of the steps to something we can conceptually understand
>>and our computers can make use of.

>
>It is being quantized, to make it digital instead of analog.


The signal prior to ADC is only analog (continuous) in your mind.
Physically, it's quantized (non-analog) as it can only take on a
finite set of values within a given range. The ADC is requantizing the
signal so it can only take on a vastly smaller number of values within
the given range.

Steve
 
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