CCD (The Charged Coupled Device) is the most commonly used light-sensitive device, and is widely used in scanners, digital cameras, digital video cameras, etc. The CCD device collects charge through the photovoltaic effect, and the charge of each row of pixels is sent to the analog shift registers on the analog signal at any time. The charge of each row of pixels is sent as a clock signal to an analog shift register and then serially converted to a voltage. Most of the silicon area is used for light collection, and the more light collected the more charge released. In design, CCD devices are expected to have extremely high signal-to-noise ratios, light sensitivity, and good dynamic range. To achieve this, specialized processors, high voltages, multiple power supplies and biases, and tight alignment of pixel points are required to form high-resolution arrays.The complexity of the CCD production process, low yields, and low yields result in high costs, making CCD devices very expensive.
CMOS (Complementary Metal Oxide Semiconductor, i.e., Complementary Metal Oxide Semiconductor) devices are a mass-produced integrated circuits with high yield, low price, etc. Relative to CCDs, CMOS device technology has a number of distinctive features:
1, integration degree High
CMOS devices can be almost all the camera required to capture all the functions integrated into a chip, because the CMOS device imaging component size is smaller, there can be more places to place the circuit, it can even be integrated into the analog-to-digital converter control chip, the image data does not have to be sent in the labyrinthine circuits, so greatly improve the capture speed. And CMOS devices are more power-saving, its power consumption is only equivalent to 1/8 of the CCD.
2, there is a good price
CMOS device structure is simple, thus high yield, low manufacturing cost. This CMOS device price than CCD has an advantage. Currently only Sony, Fuji and other five large companies can produce CCD. However, for CMOS devices, any company with 0.35 micron technology can be produced, the competition will bring down the price. Currently 300,000-pixel CMOS sensors have dropped to about $20, cheaper than CCDs, and in the megapixel market, prices will soon come down.
3, the relative shortcomings
Relative to the CCD device, CMOS devices also have its shortcomings, the sensitivity to light is not good, the signal-to-noise ratio is also very low, which leads to its image quality is difficult to compete with the CCD. However, new CMOS devices continue to push the envelope. High dynamic range CMOS devices have emerged, a technology that eliminates the need for shutter, aperture, automatic gain control, and gamma correction, and others that put an ADC on each pixel to reduce noise. Active Pixel Sensor (APS) technology improves signal-to-noise ratio and image efficiency, and approaches the image quality of a CCD. Of course, CMOS devices cannot currently compete with CCDs in high-end digital cameras. But in the consumer digital camera market, CMOS devices have begun to mature and will become the dominant technology in the low-end digital camera market in the coming years.
CCD technology: ensuring outstanding images
CCD (Charge Coupled Device) - a charge-coupled device - was invented in 1969 by Bell Labs in the United States. And PMT (Photo Multiplier Tube) - Optical Multiplier Tube, they are very successful electronic image sensor, also known as optical sensor. CCD and PMT is now widely used in many scientific products, such as fax machines, scanners, astronomical telescopes and so on. CCDs are more commonly used in digital cameras, camcorders and other miniaturized products. Traditional CCD works like a copier, the use of high-brightness light source, the manuscript in turn through the reflector, projector mirror and beam splitter, reflected in the CCD element.CCD structure can be compared to an image of a huge rotating lamp, the lamp side by side with many windows, in accordance with a certain order, to measure a certain period of time from each window into the light. Early CCDs were basically interlaced, so the image accuracy was not high. Nowadays, the scanning is generally progressive, which ensures a high resolution. the CCD is only the size of a coin, but it is very durable.
The sensors using CCD technology are generally divided into two categories, namely, general-purpose CCD sensors and special CCD sensors.
Silicon wafers and specialized large-size CCD sensor components General-purpose CCD sensors, in terms of CCD cameras have been developed. Initially CCD camera operating voltage, there are +24V, +22V, +12V and +5V and so on. With the rapid development of computer and network technology, in order to match with the PC camera and network graphics transmission, is now generally divided into +12V and +5V two kinds of operating voltage, of which the universal operating voltage is +12V. In order to reduce the cost of CCD cameras, and to improve the quality of the CCD camera many manufacturers are now committed to miniaturization and digitization of the CCD camera. Multi-layer board multi-chip integrated modular manufacturing technology to achieve the miniaturization of CCD cameras. DSP digital processing alternative to the realization of the analog system, but also the digital CCD camera has become a reality. At the same time CCD camera products are becoming increasingly diversified, such as home video recorder, TV and telephone, scanner, PDA, digital single-lens reflex camera (DSC) and so on are gradually known to the people. The main products of special type CCD sensors are electronic bombardment CCD and EBCD.
CCD application: to ensure stable performance
Along with the widespread popularity of computers, PC cameras, as the image input system of computers, are also speeding into the various families. And with the help of the Internet, synchronized communication of video and audio can also be achieved.
The rapid development of scanner technology, so that the performance of the scanner is increasingly optimized, but the price is getting lower and lower, so that the scanner really into the common people's homes. More and more users in the purchase of computers, the scanner as a standard configuration. The widespread use of scanners has increased the speed of inputting all kinds of information and charts, and the **** enjoyment of information has also been realized through the Internet.
Digital SLR cameras, as a new product developed in recent years, are a new type of image capture device. Digital cameras use CCD photosensitive devices instead of film sensitive imaging, the principle is the photoelectric effect of CCD components. In digital cameras, when the light transmitted to the CCD through the lens, the CCD will be converted to electronic signals, and then by the A/D converter into digital signals, transmitted to the DSP, and finally stored in the recording media. This, the CCD plays a very important role. the CCD is the core component of the digital camera, but also one of the most expensive components, because the cost of the CCD determines the price of the digital camera. The number of CCD elements in the photosensitive device determines the key performance of the digital camera - the resolution. There are many technical differences between different brands of digital cameras, such as Sony, Fuji and Olympus all have different performance.
High-definition digital cameras constantly require more and smaller pixel dots on the CCD. In light of this, Sony has developed 1/2-inch optical system interlaced CCDs to achieve the industry's highest level of performance. At the same time, users are demanding higher resolution, sensitivity (ISO), and signal-to-noise ratio from CCDs. It is in this environment, Fujifilm launched its own research and development of new CCD - "super" CCD.
From the invention of the CCD in the 1970s to the present day, with the development of technology, the CCD has been interlaced from the initial, low resolution, image precision is not very high, the development of progressive scanning, with a resolution of 1,200 dpi, and even up to 3,000 dpi. Moreover, the color reproduction is getting richer and richer, and the image accuracy is improving. Application of CCD technology related products are also developing rapidly. Now, most of the image products are using CCD technology, which also reflects its side in the increasingly perfect and mature.
New development of CCD technology - Super CCD technology
In principle, the higher the CCD accuracy, the higher the shooting accuracy. At the same time, it is also the core criterion for classifying digital cameras. The traditional CCD technology uses rectangular photosensitive devices arranged in a horizontal and vertical rule, in order to maintain a certain sensitivity and signal-to-noise ratio under the premise that if you want to improve the resolution can only increase the area of the CCD, which will result in a sharp rise in the manufacturing cost of digital cameras. So Fuji began to work on the CCD technology.
Fuji's engineers discovered that in our eyes, light passes through the cornea and lens to form an image on the retina, and the image is converted into a neural signal that is transmitted to the brain via the optic nerve. When the brain recognizes this information, we call it vision. The optical system of a digital camera is very similar to the structure of the human eye, the role of the lens is like the eyeball, the CCD is like the retina, and the LSI signal processor plays the role of the brain. Inspired by this, researchers have repeatedly studied the spatial resolution characteristics of the retina of the human eye, and ultimately produced a super CCD technology. Let's take a look at the features of Super CCD technology.
Improved sensitivity, signal-to-noise ratio, and dynamic range Each pixel in a conventional CCD consists of a photodiode, a control signal path, and a charge transfer path. Because the photodiode is rectangular, it is limited in size. While manufacturers have continued to add pixels to improve image quality while reducing pixel and photodiode area, inefficiencies in light absorption have become another obstacle to improving sensitivity, signal-to-noise ratio and dynamic range. Each photodiode is rectangular, while the microlens on top of it is circular - the -- the different shapes inevitably reduce light-absorption efficiency.
The super CCD uses a better solution: its pixels are all aligned at a 45° angle to form a honeycomb shape. The control signal path is eliminated, leaving more room for the photodiode. The photodiode is octagonal, very close to the circular shape of a microlens, and therefore absorbs light more efficiently. The Super CCD minimizes the space that does not contribute to image recording, the light gathering efficiency is greatly improved, the sensitivity and signal-to-noise ratio are increased, and the dynamic range is expanded.
Horizontal and Vertical Resolution Improved Comprehensive studies of human vision have shown that the spatial frequency power of image information is clustered on both the horizontal and vertical axes, with the lowest power on the 45° diagonal, an effect caused by gravity as well as other factors. This has a clear relationship to the final result of the image sensor - on the horizontal and vertical axes is the key to improved resolution, while the loss of high-frequency characteristics on the diagonal has almost no effect on image quality.
This is the idea behind the design of the super CCD - to arrange pixels that are at a 45° angle in a honeycomb format. In addition to the increased packing density, the horizontal and vertical resolution is also increased, so it better matches the characteristics of human vision. Another important factor is the availability of an LSI signal processor developed specifically for the honeycomb structure. The Super CCD and the new signal processor work together to increase the effective resolution by 60% from the previous level. This means that a super CCD with only 1.9 megapixels can perform as well as a regular CCD with 3 megapixels.
Horizontal Jump ReadoutWhile jumping pixels can significantly degrade video image quality, conventional CCDs must also use jump readout at the video output because vertical line readout is so slow. Moreover, traditional CCDs have only two colors in the pixels in the horizontal direction, and must read out two lines of data to form color. Super CCDs contain three RGB colors in each row of pixels, and in addition to vertical jump readout at 1/2 or other ratios, they can also perform horizontal 1/3 jump readout, allowing for high-quality 30 fps video output.
Simple electronic shutter In conventional CCDs, three layers of polymer coating are required to separate each pixel unit in order to prevent charge confusion between neighboring pixels, and this complex structure can be difficult to manufacture. Therefore, a mechanical shutter is usually used instead of a separating structure to read out the pixel's data in two passes. The Super CCD, however, has a much wider charge channel and is capable of transmitting data at high speeds, so the data for all pixels can be read out at once, with a simple electronic shutter. It has the potential to perform fast and precise continuous shooting.
We can prove the development of super CCD technology in digital imaging technology through the following data listed below: resolution, working with the new LSI signal processor, the effective resolution of the super CCD is 60% higher than that of an ordinary CCD; sensitivity, signal-to-noise ratio, dynamic range, the increased photodiode and higher efficiency of the light absorption properties of these indicators in the 3 megapixel When the increase of 130%, and the highlights of the level more rich; color reproduction, due to increased signal-to-noise ratio, and has a specially designed for the honeycomb structure of the LSI signal processor, color reproduction capacity increased by 50%.
Super CCD to the development and popularization of digital impact has brought new challenges and opportunities. The first to promote this technology, Fuji is sparing no effort to apply the super CCD technology on the latest products. At present, Fuji has launched the second generation of super CCD sensor, in the latest launch of FinePix 6800 zoom on the application of this chip. It has a 3.3 megapixel sensor and can get image files of up to 2832 x 2128 pixels.The FP6800 has a Super EBC aspherical lens with 3x optical zoom. It has both camera and video recording capabilities, capturing up to 160 seconds of AVI video footage, and can also be used as a digital recorder to record up to 60 minutes of audio.
CCD technology: facing many challenges
With the continuous improvement of CCD technology, a super CCD technology has been proposed in recent years. The key difference between super CCD technology and ordinary CCD technology is that ordinary CCD technology uses ordinary rectangular photodiodes, while super CCD technology uses octagonal photodiodes, and the use of pixels of 45 ° cellular arrangement. The octagonal photodiode has a more efficient absorption of light because it is closer to a microtransparent circle. The increased size of the photodiode and the improved efficiency of light absorption have resulted in a dramatic increase in the sensitivity of the CCD, so Super CCD technology has an advantage over ordinary CCD technology.
PMT (Photo Multiplier Tube) - The Photo Multiplier Tube was the first electronic sensor to appear. It has multiple electrodes built in to convert incoming light into a powerful electronic signal.PMT is often used in scanners for the publishing industry and analyzers for other industries.
CMOS technology began to be used in electronic sensors and digital cameras after 1998. The first generation of CMOS is relatively simple in principle and low in quality. in May 2000, Omnivision launched its latest CMOS chip. A new generation of CMOS chip sensitivity, signal-to-noise ratio, dynamic range and other key performance indicators, than the first generation of chips have significantly improved. CMOS is inexpensive, simple peripheral circuitry, so many industry insiders speculate that CMOS to replace the CCD of the era is not far away.
CIS contact image sensor is another photoelectric conversion device. It uses light-emitting diodes as a light source and light-sensitive components, direct contact in the surface of the manuscript to read image data.CIS structure is simple, usually only used in scanners.
PMT, CCD, CMOS, CIS is currently the most popular electronic photoreceptors. As the other three technologies become more sophisticated, CCD will be more challenged in the field of image imaging.