At present, in the field of machine vision, the most common three kinds of Sony CCD chips respectively are: ICX267A *, and ICX285A*, ICX274A *. Pixels of three kinds of chips of are different, so the corresponding resolutions are different. But there is no article on which compares and analyses these chips in-depth. Recently we technicians took some time to look through at these three Sensor manuals, including monochrome and color, looked up some documents and materials, had some discussion with colleagues, simply compared the three chips, and wrote this document below.
Due to the limited knowledge, limited time, so the scope and depth of comparative analysis is very limited, thus it is also hard to avoid some errors or omissions, we hope that readers put forward some amendments, and supplements to this article based on their own knowledge.
First:The main differences
1. Different Resolution
This difference is the most distinctive and obvious difference among the three chips. The maximum resolution of 267 chips and 285 chips are 1392 x 1040 pixels, total pixels are 1.4MP, the resolution of 274 chips is 1628 x 1236, total 2 MP.
The higher resolution, the more sharpness of the image. But the image quality is determined by comprehensive factors, in addition to the resolution, dynamic range will affect the sensitivity of CCD image quality.
2. Different Pixel Size
Pixel size of 285 chips is 6.45 * 6.45 um, pixel size of 267 and 274 chips size are smaller, for 267 chips it is 4.65*4.65 um, and for 274 chips, it is 4.40 * 4.40 um.
A Photosensitive MOS of CCD chip is like a barrel which can be used to store electric charge, the limit of charge that the bucket can hold shows the dynamic range of CCD, namely exposure latitude. The size of CCD pixels directly determines the size of the MOS. The greater the volume of MOS structure is, its ability to accommodate the charge is stronger, the dynamic range of CCD is wider, the exposure latitude is also higher and the CCD can sense more subtle changes in light, the natural color and distinct image level of image is more abounded. Conversely, the smaller the volume of a MOS is, its ability to store electric charge will drop, exposure latitude is reduced, and it is easy to see exposure charge phenomenon such as overflow, causing the image level not enough rich, prone to hot pixels. So, under the condition of the same resolution, the greater the pixel size of CCD, the higher signal to noise ratio of the image , the greater the details , and the better the general image quality .
3. Different saturation voltage Vsat
This parameter directly reflects the dynamic range of the Sensor chip, it is mainly determined by the size of pixel, As the manual data reads, for three kinds of chips, the difference of the minimum saturation voltage value is very big: 285 chip has the highest saturation voltage, it is 850 mv, 267 and 274 chips has the same saturation voltage, they are about 400 mv . It is obvious that the dynamic range of 285 chips is the largest and it can play a bigger role in the environment of large difference of area luminance.
4. Different Sensitivity
We Can see in the manual, take G channel as an example, in the case of same 1/30 seconds integral period, Sg typical values of the CCD chip are: 285 is the highest and it is 1240 mv, 420 mv for 274 , 400 mv for 267 . As you can see, 285 chip has the highest sensitivity, and minimum required illumination, and is most suitable for low illumination environment.
5. Different size of target surface
Photosensitive area of 285 chips is 2/3 inch, photosensitive area of 274 is 1/1.8 inch, and photosensitive area of 267 chips is 1/2 inch.
As we have analyzed that the size of photosensitive unit affects the performance of the CCD in the section of photosensitive area , simply put, the size, number of photosensitive unit, and photosensitive area, the three variable are mutually restricted, any two factors can determine a third one. Under the condition of the same size of CCD, when the volume of a MOS increases, its ability to hold a charge grows, the dynamic range of CCD will be wider, namely the exposure latitude is higher, of course, this will lead to the relatively reduction of CCD pixels .Conversely, the volume of a MOS is reduced while the CCD pixels relatively increased, the ability to store electrical charge is down, the ability to capture details is also down. So, sometimes, if we improve the resolution of CCD while have not changed the size of the CCD, the sharpness of the output image is raised, but signal-to-noise ratio drops, detail losses increase, the overall image quality declines.
6.The difference characteristic of spectral responds
285 chips for wavelength optical response is better,700nm wavelength of the spectral response is still larger 80%,but the blue is worse,"blue" pixel maximum peak of spectral response is not up to 75%.
7.The difference of packaging
285 is ceramic package ,267and 274 are plastic package.
Firstly ,the temperature and frequency of the ceramic are better than plastic ,but the costs are higher.Military Aerospace and the past industrial are used ceramic .The costs of plastic is lower , but the temperature and frequency are worse.
Second ,285 chip have holds for positioning on the packaging which make it easy for user to precise positioning and high resolution imaging or measurement .The precise position is so low ,267 and 274 are need welded tube to keep it fixed .
The cost of package as a proportion part of the total chip cost .When you are analyzing from the aspects of package,the cost of 285 is higher than the 267 and 274 .
8.The dark of 285 is biggest and it is 10mv ,the 267and 274 are 8mv .
This parameter is closely related to the size of the pixel .The bigger pixel size,the greater thermal and their biggest dark signal.
Different output mode .
The output mode of every CCD chip can be divided according to the transmission process which vertical register to register transfer level and the difference select of line number and method .
The 285 only have two output modes , they are :Progressive scan mode and high frame rate output mode .
The 267 have 3 output modes ,they are : Progressive scan mode,high frame rate output mode,and Superposition of pixels high frame rate output mode .
Second: Other differences
1.285and 267chip have the characteristics of Low Smear were mentioned in the manual, 274chip manual has not mentioned that . So it can be speculate the smear phenomenon of 274 will be more more serious than other two. But it just a speculate , there are no Validated.
2.The difference number of dummy , it depend on the chip structure and manufacturing process,but have no influence on performance .
3.Because of difference time of drive ,each chip have its own drive time which in the manual are detailed ,please attached the manual of CCD chip when you designing.
