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--KarlThank you both for your links and ans. It does clear things up for
me. I think it will be interesting to see how both CCD and CMOS
plays out.
ws
--
ws
--wsWhile I don't have a detaile knowledge of the low level technical
advantages of CMOS versus CCD, my guess is that it is only a matter
of time before CMOS drives CCD out of the market. The D30 at the
very least shows that CMOS is within striking distance. I have
watch CMOS for the last 20 years put other technologies into the
obsolete catagory within 5 years of its getting close in terms of
capability.
Karl
--Thank you both for your links and ans. It does clear things up for
me. I think it will be interesting to see how both CCD and CMOS
plays out.
ws
--
ws
Karl
CCD's have photo elements that cover the whole surface of the
element wheras CMOS chips require other electronic to be present on
every single cell for reading and handling of the cells which means
that every cell is actually only covered by about 70% photo element
and the rest is electronic.
CMOS are more noisy than CCD's by design and require noise
reduction circuits.
With all this Canon did an amazing job in producing a CMOS camera
that produces a very good quality image but as you can see with the
1D the obstacles sometimes cant be overcome.
I am quite sure that if canon had used a CCD in the D30 they would
have come up with an equal quality camera as well.
I cant see CMOS as being the leading chip in PRO cameras. Generally
CMOS is used in the really cheap ones such as web cams as they are
much cheaper to produce due to the use of existing hardware that
can also be used to produce other CMOS chips and in these products
noise and in general image quality isnt much of a concern. Also for
lesser quality still cameras of course.
IMHO we will find that neither CCD nor CMOS will be the winner but
something new that will be cooked up as we have this discussion.
--
Michael Salzlechner
StarZen Digital Imaging
http://www.starzen.com/imaging
E-10 / D30 Photo Albums
http://albums.photopoint.com/j/AlbumList?u=1605723
--ValliestoI keep reading from all the D30's fans about CMOS being superior. I
have been a CCD person, with both the 1D and D1x. I am just curious
what are the technical advantages of CMOS over CCD? and do you guys
see CMOS as the LEADING sensor for DSLR in the future?
Thanks
--
ws
I keep reading from all the D30's fans about CMOS being superior. I
have been a CCD person, with both the 1D and D1x. I am just curious
what are the technical advantages of CMOS over CCD? and do you guys
see CMOS as the LEADING sensor for DSLR in the future?
Thanks
--
ws
Hey, something I actually know about. I'm an electronics engineer
by the way.
CCD charge coupled device- this is not an optical sensor but a
method of reading out stored charges from semiconductor charge
wells which can be built as part of a semi-conductor photodetector.
The charges stored by the photedetectors are then read out in rows
in an analog fashion. They can then be used in analog recording
systems or converted to digital with A/D converters. This technique
can be built into the same processes used to produce high quality
photo-dectors. The materials are completely different from that
used on silicon computer chips. Typically a Gallium-Arsenide (GaAs)
substrate with Gallium-Indium-Phosphide (GaInP) detectors, or the
like. GaInP and their relatives are incompatible with Silicon
without using some type of buffer material to mate the two together.
In summary: Advanteges of CCD is it's ability to be built on the
same process as high quality photedectors.
Disadvantages: high power consumption, needs external A/D, can't
integrate electronics easily, expensive due to fancy processing and
low volume fabrication.
CMOS is again not a photosensor of any kind but a way of building
logic gates out of complementary silicon transistors. CMOS logic is
built on silicon substrates and is used to make 99.9% of all
computer chips today and as such has great advantages in terms of
volume production and ubiquity. Integrating photodetectors into a
CMOS chip opens up a world of possibilities for on-chip processing
and integration. Because silicon generally can't be used for high
quality photodetectors other types of materials must be integrated.
I'm not sure whether the D30 has some new type of silicon
photodetector or some means of making traditional photodectors
compatible with the CMOS process. My guess is it has some type of
silicon-germanium photodector with on-chip noise reduction.
In summary: Advantages of CMOS is high-volume low cost production,
low power consumption, and ability to integrate electronics with
the sensor package.
Disadvantages: Incompatibility with traditional materials used to
make high-quality photodetectors.
I think your real question should be the potential of Silicon
heterostructure photodectors vs. Gallium heterostructure
photodetectors. The short answer to this is Galium is much better
and more flexible but there is a massive push to make Silicon
feasible. Silicon will probably win out in the long run. Where
there is a will and lots of money there is a way.
Matt Peterson
Hmmm... My understanding is that traditional CCDs don't cover the whole surface of the chip with sensors. There's a lot of wiring, etc. on the surface. One of the arguments that Fuji uses for the superCCD is that they increase the relatively small surface coverage over traditional CCDs.CCD's have photo elements that cover the whole surface of the
element wheras CMOS chips require other electronic to be present on
every single cell for reading and handling of the cells which means
that every cell is actually only covered by about 70% photo element
and the rest is electronic.
So, you're saying that Fuji's claims and all of those diagrams of CCD layout showing distinct areas for photoreceptors and other wiring/features are wrong?Ron
A CCD doesnt require any additional electronics on every cell
therfor the whole cell can be effectively used as a light receptor
So, you're saying that Fuji's claims and all of those diagrams ofRon
A CCD doesnt require any additional electronics on every cell
therfor the whole cell can be effectively used as a light receptor
CCD layout showing distinct areas for photoreceptors and other
wiring/features are wrong?
Or are you saying that CMOS requires additional logic while CCDs
just require a lot of space for wiring?
--
Ron Parr
FAQ: http://www.cs.duke.edu/~parr/photography/faq.html
Gallery: http://www.pbase.com/parr/
CCD's do have a lot of wiring on top of the chip, but most light
passes through these metal layers. Only the UV light will not pass
through these layers.
Most CCD's, such as the consumer 5m pixel CCD's, have covered
"storage" areas next to each pixel (or at least every 4th pixel or
so) in order to give a real time video output. These covered
"storage" areas act as an electronic shutter.
The D30 on the other hand is a full frame device, as well as the
Nikon D1 cameras, and do not have a "storage" area. This is the
reason they do not have a LCD video preview mode. They require a
real mechanical shutter to take a photo.
Perhaps what Fuji is doing is minimizing their required storage
area with their honeycomb structure which gives them a better
optical fill factor.
Chris
CCDs make excellent detectors because they possess high quantum
efficiency, better than CMOS because the fill factor is much
higher. In a CCD, the whole pixel can collect light as opposed to a
CMOS sensor where a minimum of 3 transistors are present at each
pixel and occupy much of the real estate. CCDs are also very low
noise devices compared to CMOS readout as a result of the kTC reset
noise generated each time the sense node is reset. The reset noise
in a CCD can be completely eliminated by correlated double sampling
circuits.
CMOS imagers used in digital cameras are also monolithic devices
fabricated entirely on silicon. The photodetectors are simple p-n
junction diodes. The hybrid devices you referred to are only
necessary for specialized (scientific or military) applications.
Note that in terms of material quality, silicon is vastly superior
to GaAs. Silicon wafers as large as 12" (300 mm) in diameter are
routinely used in production as opposed to compound semiconductors
like GaAs where only 4" wafers are available. I don't know how much
experience you have with GaAs device processing but it is a
nightmare. High temperature processes easily degrade the material
and ruin the devices.
Hey, something I actually know about. I'm an electronics engineer
by the way.
CCD charge coupled device- this is not an optical sensor but a
method of reading out stored charges from semiconductor charge
wells which can be built as part of a semi-conductor photodetector.
The charges stored by the photedetectors are then read out in rows
in an analog fashion. They can then be used in analog recording
systems or converted to digital with A/D converters. This technique
can be built into the same processes used to produce high quality
photo-dectors. The materials are completely different from that
used on silicon computer chips. Typically a Gallium-Arsenide (GaAs)
substrate with Gallium-Indium-Phosphide (GaInP) detectors, or the
like. GaInP and their relatives are incompatible with Silicon
without using some type of buffer material to mate the two together.
In summary: Advanteges of CCD is it's ability to be built on the
same process as high quality photedectors.
Disadvantages: high power consumption, needs external A/D, can't
integrate electronics easily, expensive due to fancy processing and
low volume fabrication.
CMOS is again not a photosensor of any kind but a way of building
logic gates out of complementary silicon transistors. CMOS logic is
built on silicon substrates and is used to make 99.9% of all
computer chips today and as such has great advantages in terms of
volume production and ubiquity. Integrating photodetectors into a
CMOS chip opens up a world of possibilities for on-chip processing
and integration. Because silicon generally can't be used for high
quality photodetectors other types of materials must be integrated.
I'm not sure whether the D30 has some new type of silicon
photodetector or some means of making traditional photodectors
compatible with the CMOS process. My guess is it has some type of
silicon-germanium photodector with on-chip noise reduction.
In summary: Advantages of CMOS is high-volume low cost production,
low power consumption, and ability to integrate electronics with
the sensor package.
Disadvantages: Incompatibility with traditional materials used to
make high-quality photodetectors.
I think your real question should be the potential of Silicon
heterostructure photodectors vs. Gallium heterostructure
photodetectors. The short answer to this is Galium is much better
and more flexible but there is a massive push to make Silicon
feasible. Silicon will probably win out in the long run. Where
there is a will and lots of money there is a way.
Matt Peterson
I don't think they collect light that passes through any of the layers.CCD's do have a lot of wiring on top of the chip, but most light
passes through these metal layers. Only the UV light will not pass
through these layers.
The other reason is that it's an SLR. The CCD isn't receiving much or any light when the mirror is flipped the other way.The D30 on the other hand is a full frame device, as well as the
Nikon D1 cameras, and do not have a "storage" area. This is the
reason they do not have a LCD video preview mode. They require a
real mechanical shutter to take a photo.
If you're claiming that the shift registers take space on the surface of the CCD, then the honeycomb structure won't help - they'd need to make a separate advance in reducing the size of the shift registers.Perhaps what Fuji is doing is minimizing their required storage
area with their honeycomb structure which gives them a better
optical fill factor.
The difference in dust performance has nothing to do with the CMOS or CCD sensors themseves. It is the issue of sensor housing. CMOS is a well developed technology and the housing problem has long been solved. The same thing is not true for CCD.Some say dust is less on CMOS compared to CCD. With
only one CMOS based camera out - I think that comparison is unjust.
And the more one looks, I read that dust is really there on the
CMOS just as a CCD - just that it is blended into the pic quite
well that you don't notice it unless you look for it. Hence
leading to the fact that CCD will offer more detail.
I find aspects of this story somewhat incredible. Do you have a reference?Toshiba did a study of CMOS image sensors several years ago. They
took a CMOS sensor design and fabricated it on a standard CMOS line
and then took the same pixel design with slight modifications and
fabricated it on a CCD line.
It turned out that the CMOS image sensor fabed on the CCD line was
of excelent quality similar to CCD's while the CMOS line had all of
the typical noise problems. CMOS imagers typically get a bad rap
because they are usually designed for low cost and not performance.
