Advanced Imaging


Advanced Imaging Magazine

Updated: January 12th, 2011 10:01 AM CDT

Component Integration: CCD vs. CMOS

CCD has been around longer, but CMOS is closing the gap
image of a star
© NASA, ESA and Keith Noll Space Telescope Science Institute.
This image of a star, similar to our sun, 3,600 light years way ending its life was taken by Feb. 6, 2007, by the Wide Field and Planetary Camera 2 (WFPC2) on the Hubble telescope. It is actually a composite of many separate exposures made by the CCD instrument.
CMOS sensor
© Sarnoff Corp.
There are fundamental differences in architecture and operations between this CMOS sensor and a CCD sensor.

By Barry Hochfelder

And with all the differences between the two technologies, there is a common thread.

"In CMOS, for every pixel there are three MOSFETs (metal-oxide semiconductor field-effect transistors). That's a lot when you have one million pixels, so you share mosfets among four pixels. To do that you have to transfer the charge. You rely on charged coupling, which is CCD, to get a smaller transfer charge to the common nodes to share MOSFETs. CMOS needs CCD. It relies on it. Voltage to CMOS is a lot lower than CCD. It's the same process; you just tweak it differently to make it work.

"CMOS is well-fitted for the future in terms of high-speed applications."

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