Tag: Digital Camera CMOS
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Another soul CMOS sensor for digital cameras
With the release of Canon's professional-grade digital camera model EOS D30 in 2005, attention to CMOS image sensors has skyrocketed. This is because CMOS image sensors used to have the disadvantages of low signal-to-noise ratio and low resolution. Professionals have always believed that it cannot compete with CCD technology. So when Canon introduced the EOS D30 digital camera with CMOS as the photosensitive element, many people in the industry were shocked. It is incredible to use this cheap material to make the photosensitive element. It is considered that the quality of CMOS imaging cannot meet the professional requirements with high requirements. Need. So is the photosensitive element made with CMOS really worthy of the image quality? Let us first understand what CMOS is!
Technical articles
CMOS is a complementary metal oxide semiconductor. It plays an absolutely important role in the semiconductor technology of microprocessors, flash memories and application specific integrated circuits (ASICs). Both CMOS and CCD are semiconductors that can be used to sense light changes. CMOS is mainly made up of semiconductors made of "silicon" and "germanium". Basic functions are realized by negatively charged and positively charged transistors on CMOS. The current generated by these two complementary effects can be recorded and interpreted by the processing chip into an image.
The main advantage of CMOS for CCD is that it is very power efficient. Unlike CCDs made up of diodes, CMOS circuits have almost no static power consumption, and only consume power when the circuit is turned on. This makes the power consumption of CMOS only about 1/3 of that of ordinary CCD, which helps to improve the bad impression that digital cameras are "electric tigers".
The main problem with CMOS is that when dealing with fast-changing images, the current changes too often and overheats. The problem of dark current suppression is not great, and if it is not well suppressed, it is very prone to noise.
In addition, CMOS and CCD image data scanning methods are very different. For example, if the resolution is 3 million pixels, the CCD sensor can continuously scan 3 million charges. The method of scanning is very simple, as if the bucket was passed from one person to another until the last person put all the water together. Therefore, the scan can only amplify the signal after scanning the last data. Each pixel of a CMOS sensor has an amplifier that converts the charge into an electrical signal, so the CMOS sensor can amplify the signal on a per pixel basis. This method saves any inefficient transfer operations, so fast data scans can be performed with a small amount of energy consumption, while noise is reduced. This is Canon's full charge transfer technology in pixels (Figure 2).
Application
1, professional digital camera
At present, there are only a few products that use CMOS as an image sensor on a professional-grade digital single-lens reflex body, such as the Canon EOS D30, as shown in Figure 3.
We know that CMOS has been used in the metering focus system on Canon EOS series AF cameras. Canon has strong technical strength and rich experience in this area. It has become easier today to manufacture larger CMOS sensor chips at a lower cost, and CMOS can integrate image processing circuits on the chip. The D30 has a dedicated loop to control dark current. The noise reduction system works automatically when exposed for more than 1 second, which can greatly reduce noise generation. We looked at a lot of photos taken by the Canon EOS D30 and found that CMOS imaging is no worse than traditional CCDs.
As a result, we seem to have seen that CMOS will have an important place in the future development of digital cameras, and more and more professional digital cameras will consider CMOS sensors.
2, ordinary digital camera
In addition to the Canon EOS D30, CMOS sensors are basically used in ordinary civilian digital cameras. For example, Kodak's MC3 (see Figure 4) uses a CMOS sensor with a maximum resolution of 640. ×480 pixels; at the same time it can also be used as a webcam; moreover, it can be used as an MP3 player; its capacity medium is CF card, which allows users to change different capacities according to different needs. The CF card; and it provides a USB interface to connect with the computer, greatly improving the connection speed; the most important thing is that it is not only versatile, but also very close to the average home user. So we have reason to believe that the number of home digital cameras using CMOS sensors will gradually increase, making it possible for digital cameras to enter the home faster.
3, the camera
CMOS is also suitable for camera products that are not very strict in image quality. The advantage is that the manufacturing cost is lower than that of CCD, the power consumption is much lower, and the speed is faster. This is also the reason why many products using the USB interface on the market do not require an external power supply and are inexpensive. Although there is a big difference in technology, the performance difference between CCD and CMOS is not very large, but the CMOS camera has higher requirements on the light source, and most digital cameras use CCD sensors. Technically, CMOS can't achieve the same high resolution as CCD, but for 640×480 resolution cameras, CMOS is enough.
Outlook
CMOS, a low-energy, relatively easy-to-manufacture sensor, can make further efforts in terms of image sharpness and dynamic range. It is believed that CMOS is another development direction for future digital cameras. It is reported that the sales of CMOS exceeded 1 billion US dollars for the first time in 1999, and will increase by 75% every year by 2004.
In addition, CMOS sensors have increased the dynamic range of the message. Perhaps in the near future, image sensors used on most mid-range and low-end cameras will all be converted from CCD to CMOS. Most LSI manufacturers that develop CMOS image sensors in Japan believe that the market for CMOS image sensors will expand dramatically, but at least for now, in the actual use of equipment, the era of CCD image sensors and CMOS image sensors will continue.
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