CCD vs CMOS - potential

[sean]

The big deal is CMOS is much cheaper to produce and can easily integrate other smarts right on the imager. Plus CMOS uses much less power and a far lower voltage (and voltage is what indirectly attracts the dust), but the cost advantages of CMOS will make it a strong contender going foward.

CMOS is noisier, but this can be dealt with, as the D30 shows. I don't think it's clear that image quality is intrinsically different between ccd and cmos imagers; heavy processing of raw data is required to produce an image, no matter what sensor you use.

I don't know how patents will affect anyone but Canon using CMOS extensively though, at least in the short term.

-- http://www.seanansorge.com

 

[Berg Na]

From a cost, function integration, and power consumption standpoint, CMOS imagers clearly excel. For these reasons, they are the ideal choices for low cost imaging in PCs, PDAs, automobiles, and now even portable phones.

CCDs, however, still dominate the high end imaging markets primarily due to their superior performance. There's a very good article in SPIE's Optical Engineering magazine on this topic: http://oemagazine.com/fromTheMagazine/jan02/cmos.html

The big deal is CMOS is much cheaper to produce and can easily
integrate other smarts right on the imager. Plus CMOS uses much
less power and a far lower voltage (and voltage is what indirectly
attracts the dust), but the cost advantages of CMOS will make it a
strong contender going foward.

CMOS is noisier, but this can be dealt with, as the D30 shows. I
don't think it's clear that image quality is intrinsically
different between ccd and cmos imagers; heavy processing of raw
data is required to produce an image, no matter what sensor you use.

I don't know how patents will affect anyone but Canon using CMOS
extensively though, at least in the short term.

--
http://www.seanansorge.com

 

[Scott Larson]

Do all CCD's and camera sensors have microlenses to funnel light into the pixels? Are they a large expense compared to the rest of the sensor? Does anyone have a URL on how microlenses are made?

 

[Ron Parr]

Do all CCD's and camera sensors have microlenses to funnel light
into the pixels? Are they a large expense compared to the rest of
the sensor? Does anyone have a URL on how microlenses are made?

I don't know. Phil indicates that full-frame sensors don't have microlenses:

http://www.dpreview.com/learn/Glossary/Camera_System/Sensor_01.htm

Fuji indicates that their superCCD does have microlenses.

I've wondered about how this is physically realized too.

--Ron ParrFAQ: http://www.cs.duke.edu/~parr/photography/faq.htmlGallery: http://www.pbase.com/parr/

 

[Kelly Scheimberg]

Hello All,

It's a pleasure to meet the folks on this thread. I have been very impressed with the technical savvy of this group and would like to put my 2 cents in. I have been lurking for some time and have finally decided to sign-up.

Canon is not the only maker of high quality CMOS cameras, but as far as I know they are the only producer of an SLR CMOS camera. Take a look at the following site:

http://www.foveon.net/tech_f16.html

While CMOS may not replace CCDs in all applications, the potential is there to seriously challenge CCD technology in a number of markets.

Kelly

Valliesto Bailey wrote:
It maybe that the D30/D60 will be the only CMOS cameras.

SPecs from a lab test of an imager are fine, but we will only
really know if we get more real world samples.

--Kelly Scheimberg

 

[Chris Fritz]

I believe you are wrong. Standard CCD's do have gate control signals on top of the image area. I mistakenly stated that they were metal bus structures, but they are actually poly bus structures, but they are control lines. Sony CCD's are 4 phase devices and have to have 4 bus lines to each pixel + a couple additional for vertical transfer and exposure control!

The only CCD's that do not have busing ontop of the CCD is a backside illuminated device, where a CCD is fabricated in the usual method and then the silicon on the back of the device is "thinned". Then these devices are mounted in the package with the back side up.

Interline transfer devices have a metal layer to block light on every other pixel in the horizontal direction.

For a reference, you might read about astronomical backside illuminated cameras, or check out http://www.apogee-ccd.com for information.

Sorry for being so technical here.

Chris

Visible light absolutely cannot penetrate the metal layers (usually
aluminum) used for interconnections in ICs. In fact, the same metal
layers are used to block light from entering the charge storage
cells you mentioned.

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

 

[Berg Na]

I stated that there is very little metal busing in the core of a CCD, but I never implied that there are no electrical busing. Note that it makes a big difference whether the bus is designed with metal or polysilicon: Polysilicon gates can transmit light while metal lines are optically opaque. In a 4-phase CCD, each pixel is defined by 4 separate poly gates and 2 vertical channel stops. No additional gates are required for vertical charge transfer. The same gates that are used to collect charge during the integration period are used to transfer the charge during readout.

Backside illluminated CCDs are desirable for applications requiring high quantum efficiency (especially in the near UV) because the loss due to reflection and absorption in the polysilicon gates has been eliminated. However, they're a lot more expensive to fabricate. A more economical approach is chosen by Kodak which uses indium tin oxide (ITO) gates combined with microlenses to boost the QE of their CCDs. ITO gates are electrically conductive but are more 'transparent' than polysilicon.

Don't worry about getting too technical. You'd be surprised about how well informed some of the folks on this forum can be.

I believe you are wrong. Standard CCD's do have gate control
signals on top of the image area. I mistakenly stated that they
were metal bus structures, but they are actually poly bus
structures, but they are control lines. Sony CCD's are 4 phase
devices and have to have 4 bus lines to each pixel + a couple
additional for vertical transfer and exposure control!

The only CCD's that do not have busing ontop of the CCD is a
backside illuminated device, where a CCD is fabricated in the usual
method and then the silicon on the back of the device is "thinned".
Then these devices are mounted in the package with the back side up.

Interline transfer devices have a metal layer to block light on
every other pixel in the horizontal direction.

For a reference, you might read about astronomical backside
illuminated cameras, or check out http://www.apogee-ccd.com for
information.

Sorry for being so technical here.

Chris

 

[Christopher Fritz]

Most prosumer digital still cameras use interline transfer type of CCD's such as the new crop of 5M pixel cameras based on the Sony CCD sensor. This allows the camera to output video to the LCD, without the use of a mechanical shutter.

In this type of CCD, there are non-light-sensitive storage areas over about 1/2 of the image area. To improve sensitivity, this type of CCD has a microlens over this pixel to direct light from these storage areas to it's adjacent pixel.

In the Nikon D1x and Canon D30 (I don't know about the 1D), there are no such storage areas and microlenses are not required because the entire pixel is sensitive to light.

Microlenses are a very interesting technology. There is actually a glob of plastic like material implanted over each individual pixel during the CCD fabrication. Many of the recent advances in interline transfer CCD technology (other than resolution) has been better and more efficient microlens technology.

Chris

Do all CCD's and camera sensors have microlenses to funnel light
into the pixels? Are they a large expense compared to the rest of
the sensor? Does anyone have a URL on how microlenses are made?

I don't know. Phil indicates that full-frame sensors don't have
microlenses:

http://www.dpreview.com/learn/Glossary/Camera_System/Sensor_01.htm

Fuji indicates that their superCCD does have microlenses.

I've wondered about how this is physically realized too.

--
Ron Parr
FAQ: http://www.cs.duke.edu/~parr/photography/faq.html
Gallery: http://www.pbase.com/parr/

--Chris