CMOS vs CCD

[Nate Yolles]

Is there a difference between a CMOS chip and a CCD in digital SLRs? What are the benefits of each chip?

[Alvin Pingol]

Because the two technologies are substantially different, they each have their own set of benefits and drawbacks. There are many websites that outline both, with some obviously biased towards one technology over the other, but (IMO) there is not really a "superior" format - depending on the application, a CMOS censor may work significantly better than a comparable CCD, or vice-versa.

 

Kodak's CCD vs CMOS page

Dalsa's CCD vs. CMOS page

Axis Communication's CCD vs. CMOS page

[Rob Belics]

Just from a quick read it seems if you are interested in quality go with CCD. If you need small, go with CMOS.

 

Not that CMOS can't produce a quality output. As Alvin said, it depends on the conditions. But high end cameras would use a CCD.

[Nate Yolles]

Just from a quick read it seems if you are interested in quality go with CCD.

 

I haven't had a chance to read those links yet, but Nikon's 12.4mp D2X has a CMOS censor as does Canon's complete line of digital EOS including their 16.7mp 1Ds Mark II.

[Rob Belics]

CMOS can produce a quality image but, apparently, more expensively and with its inherent limitations. Is an equivalent CCD camera cheaper or larger? Or is it the same size but higher resolution?

 

There is only so much space available on any integrated circuit. Most of a CCD is dedicated to gathering light. More of a CMOS chip necessarily contains circuitry for converting and transferring pixel data.

 

What I think I would do is concentrate on the abilities of each as far as handling the light levels as stated in the articles, assuming equivalent resolution. I wouldn't care how difficult it is to manufacture or the cost and methods to make it. If two cameras cost the same then it makes no difference to me along those lines.

[Guest Daniel J. Ashley-Smith]

All I've heard is that CMOS give a much higher resolution.

[Phil Rhodes]

Hi,

 

> All I've heard is that CMOS give a much higher resolution.

 

Wrong. Resolution is more-or-less directly measurable by pixel count. An n-megapixel CMOS sensor has similar resolution to an n-megapixel CCD.

 

Phil

[Guest Daniel J. Ashley-Smith]

Hi,

 

> All I've heard is that CMOS give a much higher resolution.

 

Wrong. Resolution is more-or-less directly measurable by pixel count. An n-megapixel CMOS sensor has similar resolution to an n-megapixel CCD.

 

Phil

<{POST_SNAPBACK}>

No, I meant it in size ratio. Same sized sensor, but it holds more SPD's, or whatever CMOS has.

[John Sprung]

No, I meant it in size ratio. Same sized sensor, but it holds more SPD's, or whatever CMOS has.

<{POST_SNAPBACK}>

Again, no. Both are silicon chips, both are subject to the same minimum feature size, about 0.18 microns currently. If anything, CCD can give you more pixels per square millimeter, because it doesn't require any room for 3 to 5 transistors per pixel in the image area. In any case, you wouldn't want pixels down near the minimum feature size. You'd get no dynamic range because you don't have enough photons per pixel.

 

 

 

-- J.S.

[John Pytlak RIP]

The Kodak website also has quite a few technical papers:

 

http://www.kodak.com/global/en/digital/ccd...sArticles.jhtml

 

And a useful Digital Learning Center:

 

http://www.kodak.com/US/en/digital/dlc/index.jhtml

[John Sprung]

There is only so much space available on any integrated circuit.  Most of a CCD is dedicated to gathering light.  More of a CMOS chip necessarily contains circuitry for converting and transferring pixel data.

<{POST_SNAPBACK}>

There are quite a few fabs running 300mm wafers, and even some coming on line running 450mm wafers. So, chips bigger than a film frame are a real technical possibility. Yield being what it is, the economics of a chip for the Speed Graphic probably won't work out anytime soon, though. The ability to put lots of processing on the chip but outside the image area is a plus for CMOS. The minus is that CMOS needs 3 to 5 transistors per pixel right next to the pixel. That means you either live with some undersampling, or play with a microlens layer over the chip.

 

 

 

-- J.S.

[John Pytlak RIP]

Kodak has manufactured 16 megapixel CCD sensors on a chip about the size of a Hasselblad frame (120 size still film):

 

http://www.kodak.com/global/en/digital/ccd...F-16802CE.jhtml

 

And 14 megapixel CMOS sensors about the size of a 35mm VistaVision frame:

 

http://www.kodak.com/global/en/professiona...8.22.3.20&lc=en

 

And I can't talk about what's up on some of those satellite cameras the government bought. ;)

[Filip Plesha]

Both of these can create some good images, but the best quality

images made by a digital camera by today were made with Dalsa

and Kodak CCD's (if you count out scanning backs)

[Rob Belics]

There are quite a few fabs running 300mm wafers, and even some coming on line running 450mm wafers. So, chips bigger than a film frame are a real technical possibility.

I think you are saying this but just to make sure, even though a lab handles 300mm+ wafers does not mean they can create a single chip that big. Imperfections over such a large surface would make the yield so low that it would make each chip outrageously expensive or impossible.

 

When chips are made, they might be able to get a 20 microprocessors off one chip but out of that number maybe five are dead due to these imperfections.

 

At one time, "wafer scale integration" was floating around for using whole computer systems on one wafer but that never came about for the reasons above.

 

Now I'm saying all this having been out of the game for a number of years. ;)

[Landon D. Parks]

I dont know much about the technical differences, but I have always heard that CCD produce better overall image quality than CMOS.

 

Dont know for sure though.

[John Sprung]

I think you are saying this but just to make sure, even though a lab handles 300mm+ wafers does not mean they can create a single chip that big.  Imperfections over such a large surface would make the yield so low that it would make each chip outrageously expensive or impossible.

<{POST_SNAPBACK}>

Right. With big wafers, you can do a layout that puts chips in the VistaVision to Speed Graphic range on the disk without too much waste. But the yield problem would push the cost of 4"x5" chips so high that they'd only be a consideration for satellites or secret government projects.

 

 

 

-- J.S.