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  • CCD and CMOS main technology analysis


        CCD and CMOS are currently two imaging techniques, they are produced in the context of different manufacturing processes, current technology Introduction still each have merits. Choose CCD or CMOS IP camera should be in accordance with the applicable environmental requirements, the appropriate selection of CCD or CMOS technology, it will cause the image monitoring to achieve the desired effect. In addition, it can also be seen as a great potential for development of imaging techniques, COMS, than CCD has a strong advantage. The paper will mainly CCD and CMOS technology brief analysis, and make choices judgment.
        Traffic capture, HD IP video monitoring, applied to visual imaging technology, will be involved in the light-sensitive sensor - the CCD or CMOS imaging technology.
        Main technical characteristics of the CCD and CMOS
        For traffic capture and video surveillance, the front-end imaging the sensor CCD and CMOS more concerned about the technical characteristics of the following points.
        Electronic Shutter
        The electronic shutter is used to control the charge integration time of the chips from the beginning to the end. CCD chip is exposed to light, even if the charge transfer charge accumulation. Therefore, if the measured moving target, occurs often said Smear (smear) phenomenon. CCD is resolved with Interline Transfer (ILT) charge accumulation, each pixel is divided into the photosensitive area and the charge transfer region, the charge transfer region is not photosensitive, so that the first charge time transfer at the end of the exposure to the transfer zone, read out, so that the read-out procedure will be no charge integrator, does not produce the target movement caused Smear phenomenon. But obviously ILT way reduce the photosensitive area of ​​the pixel, and reduces the sensitivity. At this time, usually on the pixel to increase the micro-lens to collect more charge.
        CMOS chip charge are read out at each pixel does not exist the problem of the CCD chip, is the electronic shutter, Rolling shutter usually stars Rolling shutter and two Global shutter are 3T pixel structure, each time only The exposure control, i.e. the row of pixels for the next line after the line exposure exposure. Global shutter chip requires 5T structure, so that the start and end of the exposure of all pixels of the whole image. Five photodiode structure also reduces the photosensitive area, and this can also be to compensate by increasing the microlenses.
        Frame Rate
        Another important consideration is the frame rate. CCD sensor to capture and monitor the speed of the main subject to the charge read-out speed, clock and decided to read out the charge read out the pace, the higher the resolution, the slower the rate of the CCD chip read out. In fact, the upper limit of the read clock depending on the bandwidth of the optical - electrical conversion of read-out amplifier, a higher read-out rate required to have a wider bandwidth; but on the other hand, the larger the bandwidth will bring more noise , while the read-out of the high-speed high bandwidth amplifier power will increase. Therefore, the CCD sensor, high speed is a balance between the pixel resolution, noise, power consumption. The multi-channels can be provided to some extent solve the problem of the read-out speed, the image is divided into a plurality of regions, respectively, with the read-out amplifier is read out, and then flattening. Since the multi-channel circuit so that the camera larger, higher power consumption, it is not suitable for all applications.
        For the CMOS chip to a single pixel unit of the charge converted to voltage, the sense amplifier is no longer required to improve the speed to support a higher frame rate. CMOS chips easier to get a higher frame rate. At the same time, with the CCD, CMOS obtained image data can be cleared without the need to be read out. This solves the problems of the region of interest imaging, machine vision systems only image simply read out part of the image information. When only the region of interest readout applications CMOS chip can support without increasing pixel frequency based on the higher frame rate.
        Low-light Operation
        When twilight imaging, CCD and CMOS sensor technology is different, in the dim light conditions, the sense amplifier is very important, CCD readout unified amplifier, consistency is better than CMOS. Twilight conditions means that the magnitude of the signal and noise, close to the impact of noise on image quality will be great. Each CMOS the photosensitive pixel on the read-out amplifiers are low bandwidth amplifier than the high bandwidth of the amplifier noise in the CCD sensor with smaller, therefore, can obtain better signal-to-noise ratio by increasing the signal gain. Usually CCD fill factor than the CMOS must be high, the number of the charge collected under the same conditions will be more. CCD can be doubled by the charge technology, before reading out, through a multi-stage charge multiplication, each increase in the gain of the small amplitude, to obtain a higher signal-to-noise ratio. Furthermore, the pixel combination function (Binning) can also improve the sensitivity of the CCD, the N pixel Binning may enhance the SNR N times. CMOS can also similar binning often sampled superimposed on the adjacent pixel voltage signal, since the sampling will also introduce a certain amount of random noise, therefore, CMOS N pixel Binning the resulting signal-to-noise ratio enhancement can only reach times. Non-the visible imaging Other Wavelenghs.
        CCD and CMOS sensor is outside the visible spectral imaging are very different, such as an infrared (IR) light incident on the sensor chip will be played deeper than visible, so in order to fully collect these charges will need to silicon substrate is made thicker. CCD chip will be easier in the process. For CMOS process also some problems. Photosensitive silicon substrate is made thicker, the means want the other photodiode done the same thick, it will affect the performance of these control gates, amplifiers, and other devices. For ultraviolet (UV), unable to ultraviolet light through the the most IC electrode layer, or is a circuit motor layer does not respond. This leads to the front-illuminated, UV-induced response will be very weak, to solve the problems of this effect, you can remove the basal layer, back-illuminated the way. CCD sensor thinning technology has been very mature, and the thinning of CMOS technology has also made a big breakthrough.
        CCD or CMOS? Choice
        From the different impact of CCD and CMOS sensor electronic shutter, frame rate, low light level imaging and non-visible imaging technology, it is not difficult to see, to select CCD or CMOS sensor depends on the specific application. CCD technology advantage is very obvious; need to shimmer or non-visible light imaging applications need high frame rate and low-power applications, or the need for some of the region of interest imaging applications, CMOS is the better choice; if the The electronic shutter special needs, these two technologies have their advantages and disadvantages. For traffic capture, the sensor must be Global shutter, so as to avoid deformation of the license plate; same time, if the requirements are relatively high on the night effect, it is best to choose the high sensitivity of the sensor (CCD or high-end CMOS chip); In order to avoid produce smear block the license plate, should be selected CMOS, to effectively compensate for this defect; For video surveillance, real-time image and fluency is more important, so the frame rate advantage of CMOS is the best choice.
        For traffic capture and HD video surveillance, manufacturers introduced the overall solution of the major types of mature technologies integrated into high-end CMOS sensor.
        CMOS stamina to thrive
        CCD and CMOS main difference is the different photosensitive element and a different structure of the readout circuit a result of the manufacturing process. CCD sensor unit photoelectric conversion, to charge storage and to the charge transfer order of output, the process requires a dedicated process to achieve. CMOS Image Sensor unit for photodiode can be achieved in a generic CMOS integrated circuit process technology, in addition to the image processing circuit can also be integrated to achieve higher levels of integration and lower power consumption.
        Appear earlier due to CCD technology is relatively mature, accounted for most of the high-end market. Early CMOS and CCD, merely the power and cost advantages, as CMOS technology continues to progress, performance has continued to increase, and CCD technology to enhance space is limited, progress is slow.
        Apexis network camera products using CMOS technology, Apexis megapixel IP camera recommended:

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