Are there any new cameras that use CCD sensors?

Started Aug 29, 2010 | Discussions thread
Joseph S Wisniewski
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In reply to Spotpuff, Aug 30, 2010

Spotpuff wrote:

It seems like other than the S90, S95, and G11 there are no more cameras coming out with CCDs instead of CMOS.

Other than rolling shutter, I'm not sure of the drawbacks of CMOS. Articles focus on higher noise for CMOS and higher power consumption for CCD, but supposedly tech advancements have helped both technologies on their respective weaknesses.

Nope. CCD still draws 2-3 times as much power as CMOS. But what the articles never, ever got right, even going back a decade or two, is that even the most power hungry CCD sensors only account for 1/20 the power used by the camera.
Power is only an issue if you're trying to sell a lay audience on CMOS.

And advancements in CMOS did cause it to take the low noise crown from CCD. But that's mostly because the greater industry interest in CMOS cut CCD development budgets.

So what's up with CMOS? Is it just a cost-driven exercise since CMOS chips are cheaper to manufacture (but supposedly more expensive to design)?

Nope, that's another urban myth. CMOS memory and processors are cheaper to produce than CCD or CMOS image sensors, because the CMOS memory and processors are done with shallow processes: their transistors are only a fraction of a micron deep, while the photodiodes needed for an image sensor are typically some 5 microns deep.

There was a company, Fill Fatory, who tried to make a true low-cost "memory and processor" tech CMOS sensor. They're long gone.

And the "rolling shutter" isn't a CMOS characteristic, either. Either CMOS or CCD can be built with your choice of a "rolling" or "snap" shutter.

  • Snap shutters take chip space away from photodiodes, so they have poorer high ISO performance. They also have poorer blooming performance.

  • Rolling shutters give you tearing or the so-called "Jell-O effect" in video shooting.

CCD sensors were the original choice of videocamera makers, because those were done so long ago that the work to make lower noise CMOS hadn't been done yet. Because videocamera makers prefer snap shutters, small videocameras CCDs became associated with snap shutters. When the first pioneering digital still cameras were made from videocamera sensors, they "inherited" snap shutters and CCDs.

CCD sensors were also the original choice of DSLR makers like Kodak, Fuji, and AGFA (remember their DSLRs? Few do) because, again, the low light CMOS work simply hadn't been done. But they favored sensors without the snap shutter circuitry. SLRs had good shutters, already, so why not use them, eliminate the snap shutter in the sensor, and get better high ISO and less blooming? Nikon bucked this trend when they chose a snap-shutter sensor for D1.

No one here knows exactly why Canon chose to put money into making low noise CMOS. Perhaps they anticipated the need for "random access", which made things like CD-AF easier. Perhaps upper management heard the urban legend about CMOS being cheaper, and told their engineers to make it work. In either case, Canon went CMOS, and did it without a snap shutter, for the same reasons Kodak, Fuji, and AGFA did.

Anyway, to recap, there's no significant difference between CMOS and CCD in:

  • Power. ALthough there is some difference, it doesn't matter in the actual design of a camera. The sensor only uses a few percent of the total power budget.

  • Snap shutter vs. rolling shutter. Those are not CMOS or CCD characteristics.

  • Cost. Any deep process image sensor, whether CMOS or CCD, costs about the same, when built in similar quantities.

  • Performace. Given equal design resources, the two technologies perform similarly.

So, what's different?

  • Random access. You can read any part of a CMOS sensor any time you want, without having to read any other part of the sensor. read the whole thing, 10 times a second, rolling shutter style. Read 1/3 the pixels, 30 times a second for a movie mode, no problem. Read a 100 pixel square 10,000 times a second for an AF sensor? It's all good. CCDs basically are read in sequence. If you want to read part of the sensor, you have to resort to "cheats" like "dumping" unneeded lines, which can't get you part of a line, and dumps excess charge back into the chip, where it causes bleed and blooming.

  • Integrated circuitry. It's easier to add things like buffer amplifiers or A/D converters to a CMOS chip. The opto-electronic stuff is already running at the right voltage swing.

So, why are P&S cameras suddenly doing away with snap shutters? It's not a CMOS issue, it's a performance issue. Processors are getting faster. If you can barely read at the frame-rate, the "tearing" can literally be all the way across the image on a really fast pan. If you can read at twice the frame rate, you get half the tearing. By the time you hit 4 times the frame rate, most people can't tell the difference between a rolling shutter and snap shutter shot. At that point, it makes sense to drop snap shutters and gain the extra high ISO, dynamic range, and freedom from blooming of a rolling shutter sensor.

Like may technology developments, they're pushing things a little. Another year for processors to get faster, and the snap shutter will be pretty much gone.

wizfaq CMOS

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Rahon Klavanian 1912-2008.

Armenian genocide survivor, amazing cook, scrabble master, and loving grandmother. You will be missed.

Ciao! Joseph

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