CMOS vrs CCD

I am looking for a webcam to do video conferencing. Which would be a
better choice CMOS or CCD. There seems to be very little difference in
price.

Thanks
Charlie

 

Neither is categorically superior to the other, although vendors selling
only one technology often claim otherwise. The choice depends far more on
the application...and the vendor.
Both types of imagers convert light into electric charge and process it into
electronic signals. In a CCD sensor, every pixel's charge is transferred
through a very limited number (often one) of output nodes to be converted to
voltage, buffered, and sent off-chip as an analog signal. All of the pixel
can be devoted to light capture, and the output's uniformity (a key factor
in image quality) is high. In a CMOS sensor, each pixel has its own
charge-to-voltage conversion, and the sensor often also includes
digitization circuits, so that the chip outputs digital bits. These other
functions reduce the area available for light capture, and with each pixel
doing its own conversion, uniformity is lower. But the chip requires less
off-chip circuitry for basic operation. (For more details on device
architecture and operation, see "CCD vs. CMOS: Facts and Fiction" (385k
PDF).)

CCDs have been the dominant solid-state imagers since the 1970s, primarily
because CCDs gave far superior images with the fabrication technology
available. CMOS image sensors required more uniformity and smaller features
than silicon wafer foundries could deliver at the time. DALSA founder and
CEO Dr. Savvas Chamberlain was a pioneer in developing both technologies in
the 1960s, and his leadership helped bring CCD technology forward. Only
recently has semiconductor fabrication advanced to the point that CMOS image
sensors can be useful and cost-effective in some mid-performance imaging
applications.

CCDs offer superior image performance (as measured in quantum efficiency and
noise), and flexibility at the expense of system size. They continue to rule
in the applications that demand the highest image quality, such as most
industrial, scientific, and medical applications.

CMOS imagers offer more integration (more functions on the chip), lower
power dissipation (at the chip level), and smaller system size at the
expense of image quality and flexibility. They are well-suited to
high-volume, space-constrained applications where image quality is not
paramount, such as security cameras, PC peripherals, toys, fax machines, and
some automotive applications.

Costs are similar at the chip level. Early CMOS proponents claimed CMOS
imagers would be much cheaper because they could be produced on the same
high-volume wafer processing lines as mainstream logic or memory chips. This
has not been the case. The accommodations required for good imaging
perfomance have limited CMOS imagers to specialized, lower-volume
mixed-signal fabrication processes. CMOS imagers also require more silicon
per pixel. CMOS cameras may require fewer components and less power, but
they may also require post-processing circuits to compensate for the lower
image quality.

The larger issue around pricing is sustainability. Since many CMOS start-ups
pursue high-volume, commodity applications from a small base of business,
they must price below costs to win business. For some, the risk will pay off
and their volumes will provide enough margin for viability. But others will
have to raise their prices, while still others will go out of business
entirely. High-risk startups can be interesting to venture capitalists, but
imager customers require long-term stability and support.

The money and attention concentrated on CMOS imagers means that their
performance will continue to improve, eventually blurring the line between
CCD and CMOS image quality. But for the forseeable future, CCDs and CMOS
will remain complementary. Each can provide benefits that the other cannot.
DALSA's approach is "technology-neutral": we are one of the few vendors able
to offer real solutions with both CCDs and CMOS.

More info here http://www.dalsa.com/markets/ccd_vs_cmos.asp


--


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Charlie wrote with a thumbnail dipped in tar:

CMOS based cameras should be cheaper to manufacture due to economies of
scale. Every MB has a CMOS chip, remember.

 

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