CCD refers to a charge-coupled device. It is a detection element that expresses the size of a signal with the amount of charge and transmits the signal in a coupled manner. It has self-scanning, wide spectrum range, small distortion, small size, light weight, low system noise, and power consumption. It has a series of advantages such as small size, long life and high reliability, and can be made into a highly integrated assembly. Charge-coupled device (CCD) is a new type of semiconductor device developed in the early 1970s.
CCD is widely used in digital photography, astronomy, especially optical telemetry technology, optical and spectrum telescopes and high-speed photography technology, such as Lucky imaging. CCD is widely used in cameras, digital cameras and scanners, but the dot matrix CCD is used in the camera, which includes x and y directions for capturing planar images, and the scanner uses a linear CCD, which only has The x-direction and y-direction scanning are completed by the scanner's mechanical device.
History of CCD
CCD was invented by Will Lab S. Boyle and George E. Smith of Bell Labs in 1969. Bell Labs was developing video phones and semiconductor bubble memory. After combining these two new technologies, Boyle and Smith came up with a device that they named "Charge "Bubble" Devices". The characteristic of this device is that it can transfer charge along the surface of a piece of semiconductor, and it was tried to be used as a memory device. At that time, it was only possible to input memory by means of "injecting" charge from the temporary memory. But then it was found that the photoelectric effect can cause charges on the surface of such devices to form digital images. By the 1970s, researchers at Bell Labs were able to capture images with a simple linear device, and CCD was born. Several companies continued this invention and proceeded with further research, including Fairchild Semiconductor, RCA, and Texas Instruments. Among them, the products of Fast Semiconductor are leading in the market. In 1974, a 500-unit linear device and a 100x100 pixel flat device were released.
1. HAD sensor
HAD (HOLE-ACCUMULATION DIODE) sensor is on the surface of N-type substrate, P-type, N+2 polar body, plus positive hole accumulation layer, which is SONY's unique structure. Due to the design of this positive hole accumulation layer, the dark current problem often found on the sensor surface can be solved. In addition, designing a vertical tunnel through which electrons can pass on the N-type substrate increases the aperture ratio, in other words, also improves the sensitivity. In the early 1980s, Sony used its lead in variable-speed electronic shutter products to obtain clear images when shooting fast-moving objects.
2. ON-CHIP MICRO LENS
In the late 1980s, as each pixel in the CCD shrank, the light-receiving area was reduced, and the sensitivity became lower. In order to improve this problem, Sony installs tiny lenses in front of each photodiode. After using tiny lenses, the photosensitive area is no longer determined by the opening area of the sensor, but by the surface area of the tiny lenses. Therefore, the aperture ratio is improved in the specifications, and the brightness is greatly improved.
3. SUPER HAD CCD
Since the late 1990s, the unit area of the CCD has become smaller and smaller. The tiny lens technology developed in 1989 can no longer increase the brightness. If the magnification of the internal amplifier of the CCD component is increased, the noise will also be improved. , The picture quality will be significantly affected. Sony has gone a step further in the research and development of CCD technology. It has improved the technology that used tiny lenses to improve light utilization, and developed a technology that optimizes the shape of the lens, that is, Sony Superhad CCD technology. Basically, it is a design that improves the light utilization efficiency to enhance the sense of brightness, which also laid the foundation for the recent basic CCD technology.
4. NEW STRUCTURE CCD
With the continuous increase of the aperture F value of the camera's optical lens, more and more oblique light enters the camera, so that the light incident on the CCD component cannot be 100% focused on the sensor, and the CCD sensor's The sensitivity will decrease. In 1998, Sony improved the problem by adding a layer of internal lenses between the color filter and the shading film. Adding this layer of lens can improve the internal optical path, so that oblique light can also be focused on the photoreceptor. At the same time, the insulating layer between the silicon substrate and the electrode is thinned, so that signals that cause noise in the vertical CCD screen will not enter, and the SMEAR characteristics are improved.
5. EXVIEW HAD CCD
Infrared light with a longer wavelength than visible light can also be photoelectrically converted in a semiconductor silicon chip. However, until now, the CCD cannot collect these photoelectrically converted charges into the sensor in an effective way. To this end, Sony's newly developed "EXVIEW HAD CCD" technology in 1998 can effectively convert the near-infrared light that has not been effectively used into image data. The visible light range is expanded to infrared rays, so that the sense of brightness can be greatly improved. When using the "EXVIEWHAD CCD" component, high-brightness photos can be obtained even in a dark environment. Moreover, when the photoelectric conversion was done in the deep layer of the silicon wafer, the SMEAR component leaked into the vertical CCD part can also be collected into the sensor, so the noise affecting the image quality will be greatly reduced.
In January 2006, Boyle and Smith were awarded the Charles Stark Draper Medal by the Institute of Electrical and Electronics Engineers (IEEE) in recognition of their contribution to the development of CCD.
On October 6, 2009 Beijing time, the 2009 Nobel Prize in Physics was announced. The Nobel Prize Committee of the Royal Swedish Academy of Sciences announced the award of the award to a Hong Kong Chinese scientist Charles K. Kao and two scientists Vera. Boyle (Willard S. Boyle) and George Smith (George E. Smith). Scientist Charles K. Kao won the award for "a pioneering achievement in the transmission of light in the field of optical communications", and scientists Boyle and George-E-Smith "invented the imaging semiconductor circuit-charge coupled device image sensor CCD" Won this award.
The CCD image sensor can directly convert the optical signal into an analog current signal. The current signal undergoes amplification and analog-to-digital conversion to achieve image acquisition, storage, transmission, processing, and reproduction. Its salient features are:
1. Small size and light weight;
2. Low power consumption, low working voltage, anti-shock and vibration, stable performance and long life;
3. High sensitivity, low noise and large dynamic range;
4. Fast response speed, self-scanning function, small image distortion, no afterimage;
5. It is produced by ultra-large scale integrated circuit technology, with high pixel integration, accurate size, and low commercial production cost. Therefore, many instruments that use optical methods to measure the outer diameter use CCD devices as photoelectric receivers.
Working principle of CCD
CCD can be divided into two categories: linear array CCD and area array CCD. Linear CCD usually divides the internal electrodes of the CCD into arrays, each group is called a phase, and the same clock pulse is applied. The required number of phases is determined by the internal structure of the CCD chip. CCDs with different structures can meet the requirements of different occasions. The linear array CCD is divided into a single channel and a double channel, and its photosensitive area is a MOS capacitor or photosensitive diode structure, and the production process is relatively simple. It consists of a photosensitive area array and a shift register scanning circuit. It is characterized by fast information processing, simple peripheral circuits, and easy real-time control, but it has a small amount of information obtained and cannot process complex images (linear array CCD is shown on the right) . The structure of the area array CCD is much more complicated. It consists of many photosensitive areas arranged in a square array and connected into a device in a certain form. It has a large amount of information and can process complex images.
1. Spectral sensitivity
The spectral sensitivity of the CCD depends on parameters such as quantum efficiency, wavelength, and integration time. Quantum efficiency characterizes the photoelectric conversion ability of CCD chips to optical signals of different wavelengths. CCD chips made by different processes have different quantum efficiencies. Sensitivity is also related to the illumination mode. The back-illuminated CCD has high quantum efficiency, and the spectral response curve has no fluctuations. There are several peaks and valleys on the spectral response curve of the front-illuminated CCD due to reflection and absorption losses.
2. Dark current and noise of CCD
The CCD dark current is caused by internally excited carriers. When the CCD is operating at a low frame rate, a low-brightness image can be collected with an accumulation (exposure) time of several seconds or thousands of seconds. If the exposure time is long, dark current will fill the potential well with hot electrons before the photoelectrons are formed. Due to the defects of the lattice lattice, the dark current of different pixels may vary greatly. On images with long exposure time, a star-shaped fixed noise pattern will be generated. This effect is because a few pixels have abnormally large dark current, which can generally be subtracted from the image after recording, unless the dark current has saturated the electrons in the potential well.
The defects of the lattice lattice produce dead pixels that cannot collect photoelectrons. Since the charge passes through the pixels on the way out of the chip, a dead pixel will cause all or part of the pixels in a row to be invalid; transient exposure will cause excess photoelectrons to spread to adjacent pixels, resulting in blurred image diffusivity.
3. Transfer efficiency and transfer loss rate
When a charge packet is transferred from one potential well to another, a process is required. The charge in the pixel must move thousands of times or more between the potential wells before leaving the chip, which requires extremely high charge transfer efficiency, otherwise the effective number of photoelectrons will be seriously lost during the readout process.
The main reason for the incomplete charge transfer is the capture of electrons by the surface state, and the transfer loss causes signal degradation. Using "fat zero" technology can reduce this loss.
4. Upper and lower limits of clock frequency
The lower limit depends on the average lifetime of non-equilibrium carriers, and the upper limit depends on the loss rate of charge packet transfer, that is, there must be sufficient time for charge packet transfer.
5. Dynamic range
Characterizes the ratio of the strongest but unsaturated points to the weakest point in the same image. Digital images are generally represented by DN.
Characterize the inconsistency of the response of all pixels of the CCD chip to the same wavelength and the same intensity signal
Characterize the inconsistency of the output signal strength of the CCD chip with the input signal of the same wavelength.
8. Time constant
Characterize the response speed of the detector, and also indicate the modulated radiation capability of the detector response. The time constant is related to the life of free carriers in light guides and photovoltaic detectors.
9. CCD chip pixel defects
a. Pixel defect: For illumination in the linear range of 50%, if the pixel response deviates from its neighboring pixels by more than 30%, it is a pixel defect.
b. Cluster defects: within the range of 3*3 pixels, the number of defects exceeds 5 pixels.
c. Column defects: In the range of 1*12, the column defects exceed 8 pixels.
d. Line defects: Within a group of horizontal pixels, line defects exceed 8 pixels.
There are two ways to transfer photocharges: CCD surface channel (SCCD) and bulk channel (BCCD, also known as buried channel CCD). The charge transfer path of the surface channel CCD is closer to the semiconductor-insulator interface. The process is simple and the dynamic range is large. However, the transfer of signal charge is affected by the surface state. The transfer speed and transfer efficiency are low. The operating frequency is generally below 10MHz. In order to eliminate this phenomenon, in order to improve the working speed of the CCD, the structure of the channel is transferred by the ion implantation method, so that the minimum value of potential energy leaves the interface and enters the interior of the substrate, forming a transfer channel in the body, avoiding the influence of the surface state This is the body channel CCD. The transfer efficiency of the body channel CCD is greatly improved, the operating frequency can be as high as 100MHz, and can be made into a large-scale device.
The research on CCD devices and their application technologies has made amazing progress, especially in the fields of image sensing and non-contact measurement. With the continuous development of CCD technology and theory, the breadth and depth of the application of CCD technology will be greater and greater. CCD is integrated with a high-sensitivity semiconductor material, which can generate the corresponding charge signal according to the light irradiated on its surface, which is converted into a "0" or "1" digital signal by an analog-to-digital converter chip. After the digital signal is compressed and arranged by the program, it can be converted into an electronic image signal that can be recognized by the computer by the flash memory or the hard disk card, and the received light signal can be accurately measured and analyzed.
CCDs with grid-shaped pixels are used in the photosensitive elements of digital cameras, optical scanners and cameras. Its light efficiency can reach 70% (it can capture 70% of incident light), which is better than 2% of traditional film (negative film), so CCD is quickly adopted by astronomers.
After the linear CCD image used by the facsimile machine is imaged on the surface of the capacitor array through the lens, depending on the intensity of its brightness, a charge of varying strength is formed on each capacitor unit. A linear CCD for a fax machine or a scanner captures a long strip of light and shadow at a time, while a flat CCD for a digital camera or a camera captures an entire image at a time, or extracts a square area from it. Once the exposure is completed, the control circuit will transfer the charge on the capacitor unit to the next next unit. When the last unit at the edge is reached, the charge signal will be transferred to the amplifier and transformed into a potential. This is repeated until the entire image is converted to potential, sampled and digitized, and stored in memory. The stored images can be transferred to a printer, storage device or display.
Ultra-high-resolution CCD chips are still quite expensive. Static cameras equipped with 3CCDs often exceed the budget of many professional photographers. Therefore, some high-end cameras use rotating color filters.
The frozen CCD was also widely used in astrophotography and various night vision devices in the early 1990s, and large observatories have also continuously developed high-pixel CCDs to take extremely high-resolution celestial photos.
CCD has a wonderful application in astronomy, which can make fixed telescopes function like tracking telescopes. The method is to make the direction of charge reading and movement on the CCD consistent with the direction of the celestial body movement, and the speed is also synchronized. The CCD guide star can not only enable the telescope to effectively correct tracking errors, but also enable the telescope to record a larger field of view than the original.
Most CCDs can sense infrared light, so infrared images, night vision devices, and cameras (cameras) with zero illumination (or approaching zero illumination) are derived. In order to reduce infrared interference, astronomical CCDs are often cooled with liquid nitrogen or semiconductors, because objects at room temperature will have infrared blackbody radiation effects. The sensitivity of CCD to infrared rays causes another effect. If a digital camera or video recorder equipped with CCD is not equipped with an infrared filter, it is easy to capture the infrared rays emitted by the remote control. Reducing the temperature can reduce the dark current on the capacitor array, improve the sensitivity of the CCD in low illumination, and even increase the sensitivity to ultraviolet and visible light (increased signal-to-noise ratio).
Temperature noise, dark current and cosmic radiation all affect the pixels on the surface of the CCD. Astronomers use the opening and closing of the shutter to expose the CCD multiple times and take the average value to mitigate the interference effect. In order to remove background noise, the average value of the image signal when the shutter is closed is the "dark frame". Then open the shutter, subtract the value of the dark frame after obtaining the image, and then filter out the system noise (dark spots and bright spots, etc.) to get clearer details.
The cooled CCD camera used in astrophotography must be fixed at the imaging position with a ring to prevent the influence of external light or vibration; at the same time, because most imaging platforms are born cumbersome, to shoot images of faint celestial bodies such as galaxies and nebulae, astronomers use "automatic guidance" Star" technology. Most automatic guide star systems use additional CCDs with different axes to monitor any image shifts. However, some systems connect the main mirror to the CCD camera used for shooting. Using an optical device to add the star light inside the main mirror to another CCD star guide device in the camera, it can quickly detect small errors in tracking celestial bodies, and automatically adjust the drive motor to correct the error without the need to install another star guide.
In fact, in the CCD, it is sensitive to infrared light and can see infrared light, for example: using a black and white camera, with the bright electric light turned off, turn on the infrared light, you can immediately see the image. This is because black and white cameras are inherently colorless, but most color CCDs used in reality do not see infrared light. In fact, the color CCD can also recognize and sense infrared rays, but it will interfere with the operation of the DSP (image processing main chip) to cause "color cast". Therefore, in order to make it not "color cast" in the color CCD, the color CCD The filter sticking on top prevents it from receiving infrared rays.
The transmittance from 380nm-645nm is about 93%, which is just the range of visible light (purple-indigo-blue-green-yellow-orange-red), which is the color of the rainbow. More than 600nm is red light, and when it goes to the right, it is called "infrared". It is "light other than red". It is not red light, because the eye can no longer see it. Come again, what our eyes see around 380nm It is purple, and it is called "ultraviolet" when it is "outside" at 380nm.
In general color digital cameras, a Bayer filter is added to the CCD. Every four pixels form a unit, one is responsible for filtering red, one filtering blue, and two filtering green (because human eyes are more sensitive to green). As a result, each pixel receives the photosensitive signal, but the color resolution is not as good as the photosensitive resolution.
A 3CCD system composed of three CCDs and a beam splitter prism can separate colors better. The beam splitter prism can analyze incident light into three colored lights of red, blue, and green, and each of the three CCDs is responsible for imaging one of the colored lights. All professional digital cameras and some semi-professional digital cameras use 3CCD technology.
As of 2005, ultra-high resolution CCD chips are still quite expensive. Static cameras equipped with 3CCDs often cost more than the budget of many professional photographers. Therefore, some high-end cameras use rotating color filters. This type of multiple imaging camera can only be used to shoot static objects.
The CCD is made of a high-sensitivity semiconductor material, which can convert light into electric charge, and convert it into digital signals through an analog-to-digital converter chip. The digital signals are compressed and stored by the camera's internal flash memory or built-in hard disk card. Therefore, the data can be easily transmitted to the computer, and the image can be modified according to the needs and imagination with the help of the processing means of the computer. CCD is composed of many photosensitive units, usually in units of megapixels. When the surface of the CCD is exposed to light, each photosensitive unit reflects the charge on the component, and the signals generated by all the photosensitive units are added together to form a complete picture.
CCD is an extremely important component in the camera. It plays the role of converting light into electrical signals, similar to human eyes, so its performance will directly affect the performance of the camera.
There are many indicators to measure the quality of the CCD, including the number of pixels, CCD size, sensitivity, signal-to-noise ratio, etc. Among them, the number of pixels and CCD size are important indicators. The number of pixels refers to the number of photosensitive elements on the CCD. The picture taken by the camera can be understood as composed of many small dots, each dot is a pixel. Obviously, the more pixels, the clearer the picture. If the CCD does not have enough pixels, the sharpness of the picture will be greatly affected. Therefore, in theory, the more pixels the CCD should be, the better. However, the increase in the number of CCD pixels will reduce the manufacturing cost and yield, and under the current TV standards, after the number of pixels increases to a certain number, then the effect of increasing the clarity of the shooting picture becomes less obvious. A pixel count of around one million is sufficient for general use.
Single CCD camera means that there is only one CCD in the camera and use it to perform photoelectric conversion of the luminance signal and the color signal. The chrominance signal is completed by some specific color mask devices on the CCD in combination with the following circuit. Since a CCD completes the conversion of the luminance signal and the chrominance signal at the same time, it is inevitable that the two will complete, so that the captured image will not meet the professional level requirements in color reproduction. In order to solve this problem, 3CCD cameras appeared. 3CCD, as the name suggests, is that a camera uses 3 CCDs. We know that after passing through a special prism, light will be divided into three colors: red, green, and blue. These three colors are the three primary colors used by our TV. Through these three primary colors, the brightness signal can be generated. All TV signals included. If you use a CCD to receive each color and convert it into an electrical signal, and then process the circuit to generate an image signal, this constitutes a 3CCD system.
Compared with a single CCD, 3CCD uses three CCDs to convert red, green, and blue signals, respectively. The captured image is more natural in color reproduction than a single CCD, and its brightness and resolution are also better than a single CCD. However, due to the use of three CCDs, the price of a 3CCD camera is much more expensive than a single CCD.
The four-color CCD is a new CCD technology introduced by Sony in 2003. The four colors are red, green, blue, and magenta (RGBE). Compared with the traditional three colors (red, green, and blue), the color reproduction error rate of the four-color CCD is further reduced. Therefore, the color reproduction is more realistic. The first digital camera with four-color CCD is SONY DSC—F828
An area array CCD
The column of CCD in the specification table of digital cameras often reads "1/2.7 inch CCD" and so on. The "1/2.7" here is the size of the CCD, which is actually the length of the diagonal of the CCD.
Existing digital cameras generally use CCDs of 1/2.7 inch, 1/2.5 inch and 1/1.8 inch. The CCD is a collection of light-receiving elements (pixels), which receives light transmitted through the lens and converts it into electrical signals. In the case of the same number of pixels, the larger the CCD size, the larger the unit pixel. In this way, the unit pixel can collect more light, so in theory, it can be said to help improve the image quality.
However, the quality of digital cameras is not only determined by the CCD. The performance of the lens and the circuit that forms an image through the electrical signals output by the CCD can also affect the image quality of the camera. The so-called "large size CCD = high image quality" is incorrect. For example, although 1/2.7 inches are smaller than 1/1.8 inches, digital cameras equipped with 1/2.7 inches CCDs have not been criticized for poor image quality.
Today, compact digital cameras are becoming more compact and lighter. For design considerations, most of them use small CCDs of 1/2.7 inches.
By the way, the "type" of 1/2.7 inches is sometimes also written as "inch", but here is not the ordinary "1 inch = 25.4mm". Due to the combination of the camera tube and display method used on the camera before the CCD was unveiled, it is customary to use a special size. 1/2.7 inch is 6.6mm, 1/1.8 inch is about 9mm.
Data of CCD structure and working principle (from Chinese instrument supermarket):
The CCD structure includes items such as photodiode, shift signal register, parallel signal register, signal amplifier, analog-to-digital converter, etc., which will be described as follows;
2. Shift signal register (Shift Register): used to temporarily store the charge generated after the photosensitive.
3. Parallel signal register (Transfer Register): used to temporarily store the analog signal of the parallel accumulator and amplify the charge transfer.
4. Signal amplifier: used to amplify weak electrical signals.
5. Analog-to-digital converter: converts amplified electrical signals into digital signals.
The working principle of CCD consists of three layers, such as micro lens, color separation filter, and photosensitive layer, which will be described as follows;
The micro lens is the first layer of the CCD. We know that the key to digital camera imaging lies in its photosensitive layer. In order to expand the CCD's lighting rate, the light receiving area of a single pixel must be expanded. However, the way to improve the lighting rate is also easy to reduce the image quality. This layer of "miniature lens" is equivalent to adding a pair of glasses in front of the photosensitive layer. Therefore, the photosensitive area is no longer determined by the opening area of the sensor, but by the surface area of the micro lens.
2. Separation filter
The color separation filter is the second layer of the CCD. There are two color separation methods, one is the RGB primary color separation method, and the other is the CMYK complementary color separation method. These two methods have their own advantages and disadvantages. First, let’s first understand the concept of two color separation methods. RGB is the three primary color separation method. Almost all colors that can be recognized by the human eye can be composed of red, green and blue, and the three letters of RGB are Red, Green and Blue, which shows that RGB color separation method is adjusted by the color of these three channels. Let's talk about CMYK, which is made up of the colors of the four channels. They are cyan (C), magenta (M), yellow (Y), and black (K). In the printing industry, CMYK is more suitable, but its adjusted color is not as much as RGB.
The advantage of the primary color CCD is the sharp image quality and true color, but the disadvantage is the noise problem. Therefore, you can note that most digital cameras using primary color CCDs will probably not exceed 400 in ISO sensitivity. In contrast, the complementary color CCD has an additional Y-yellow color filter, which is more careful in color resolution, but sacrifices the resolution of some images. On the ISO value, the complementary color CCD can tolerate higher sensitivity, generally all Can be set above 800
3. Photosensitive layer
The photosensitive layer is the third layer of the CCD. This layer is mainly responsible for converting the light source passing through the color filter layer into an electronic signal and transmitting the signal to the image processing chip to restore the image.
The CCD chip is like the human retina, which is the core of the camera. At present, China has no ability to manufacture. Most of the cameras on the market use chips made by companies such as Japanese SONY, SHARP, Panasonic, and Fuji. They are also capable of production for South Korea’s Samsung, but the quality is slightly inferior. Because the chips are produced in different grades and the manufacturers have different ways to obtain them, the CCD acquisition effect is also very different. At the time of purchase, you can take the following methods to detect: turn on the power, connect the video cable to the monitor, close the lens aperture, see if there are bright spots when the image is completely dark, the snowflakes on the screen are not big, these are the most simple and direct detection of the CCD chip Method, and no other special instruments are needed. Then you can open the iris and see a still life. If it is a color camera, it is best to take a brightly colored object to see if the image on the monitor is distorted, distorted, and whether the color or grayscale is smooth. A good CCD can restore the color of the scene very well, so that the object looks clear and natural; and the image of the defective product will have a color cast phenomenon, even if it is faced with a white paper, the image will show blue or red. Some CCDs will have impurities on the CCD target surface due to the dust in the production workshop. In general, the impurities will not affect the image, but in low light or microscopic photography, fine dust can also cause undesirable consequences. Such work must be carefully selected.
1. By imaging color
Color camera: It is suitable for distinguishing details of sceneries, such as distinguishing the color of clothing or sceneries.
Black and white camera: suitable for areas with insufficient light and areas where lighting equipment cannot be installed at night. When only monitoring the position or movement of the scene, a black and white camera can be used. For scientific research with high imaging requirements, black and white cameras are also generally chosen, because many cameras take pictures that are closer to real objects than color photos (because color pictures are pictures processed by filter light, and black and white photos are Photos formed by unprocessed light)
2. Divided by resolution sensitivity
Those with image pixels of less than 380,000 are of the general type, among which the products with 250,000 pixels (512*492) and resolution of 400 lines are the most common.
High-resolution type with more than 380,000 image pixels.
3. According to the size of CCD target surface
CCD chips have been developed in various sizes:
Most of the chips used recently are 1/3" and 1/4". When purchasing a camera, especially when there are strict requirements on the camera angle, the size of the CCD target surface, the cooperation between the CCD and the lens will directly affect the size of the field of view angle and the clarity of the image.
1 inch-the size of the target surface is 12.7mm wide * 9.6mm high, and the diagonal is 16mm.
2/3 inches-the target size is 8.8mm wide * 6.6mm high, and the diagonal is 11mm.
1/2 inch-the target size is 6.4mm wide * 4.8mm high, and the diagonal is 8mm.
1/3 inch-the target size is 4.8mm wide * 3.6mm high, and the diagonal is 6mm.
1/4 inch-the target size is 3.2mm wide * 2.4mm high, and the diagonal is 4mm.
4. According to the scanning system
PAL system, NTSC system. China uses the interlaced scanning (PAL) system (black and white is CCIR), the standard is 625 lines, 50 fields, and only some non-standard systems are used in medical or other professional fields. In addition, Japan is NTSC, 525 lines, 60 fields (black and white is EIA).
5. By power supply
110VAC (mostly NTSC standard)
9VDC (mostly miniature cameras belong to this category).
6. Divided by synchronization
Internal synchronization: Use the synchronization signal generated by the synchronization signal generation circuit in the camera to complete the operation.
External synchronization: An external synchronization signal generator is used to send the synchronization signal to the external synchronization input of the camera.
Power synchronization (linear lock, line lock): Use the camera AC power to complete the vertical push synchronization.
External VD synchronization: Input the VD synchronization pulse on the camera signal cable to complete the external VD synchronization.
Multi-camera external synchronization: fixed external synchronization to multiple cameras, so that each camera can work under the same conditions, because each camera is synchronized, so even if one of the cameras is converted to other scenes, the synchronized camera's picture will not distortion.
7. According to degree, CCD is divided into
Normal type Illumination required for normal work 1~3LUX
Moonlight type Illumination required for normal work is about 0.1LUX
Starlight type Illumination required for normal operation is less than 0.01LUX
Infrared type: Illuminated by infrared lamp, it can image even when there is no light
CCD size, which is the target surface of the camera. It was originally 1/2 inch, 1/3 inch has been popularized, and 1/4 inch and 1/5 inch have also been commercialized.
CCD pixel is the main performance index of CCD. It determines the clarity of the displayed image. The higher the resolution, the better the performance of the image details. CCD is composed of area array photosensitive elements. Each element is called a pixel. The more pixels, the clearer the image. A few days ago, most of the market demarcated 250,000 and 380,000 pixels, and those with more than 380,000 pixels were high-definition cameras.
Horizontal resolution. The typical resolution of a color camera is between 320 and 500 TV lines, mainly with 330 lines, 380 lines, 420 lines, 460 lines, 500 lines and other different grades. The resolution is expressed by TV lines (referred to as TV LINES), and the resolution of the color camera is between 330 and 500 lines. The resolution is related to the CCD and the lens, and is also directly related to the bandwidth of the camera circuit channel. The general rule is that the bandwidth of 1MHz is equivalent to a resolution of 80 lines. The wider the frequency band, the clearer the image, and the larger the line value.
Minimum illumination, also called sensitivity. It is the sensitivity of the CCD to ambient light, or the darkest light required for normal CCD imaging. The unit of illuminance is LUX. The smaller the value, the less light is required and the more sensitive the camera. Moonlight-level and starlight-level high-sensitivity cameras can work in very dark conditions. 2 to 3 lux is general illumination. A few days ago, ordinary cameras with less than 1 lux came out.
Scanning system. There are PAL system and NTSC system.
Camera power supply. The AC has 220V, 110V, 24V, and the DC is 12V or 9V.
Signal to noise ratio. The typical value is 46db, if it is 50db, the image has a little noise, but the image quality is good; if it is 60db, the image quality is excellent, and no noise appears.
Video output. Mostly 1Vp-p, 75Ω, all using BNC connectors.
Lens installation method. There are C and CS methods, the difference between the two is that the photosensitive distance is different.
Choice of synchronization method
A. For a single camera, the main synchronization methods are as follows:
Internal synchronization-use the crystal oscillation circuit inside the camera to generate a synchronization signal to complete the operation.
External synchronization-use the synchronization signal generated by an external synchronization signal generator to send to the external synchronization input terminal of the camera to achieve synchronization.
Power supply synchronization-also known as linear lock or line lock, is to use the AC power of the camera to complete the vertical push synchronization, that is, the camera and the power supply zero line synchronization.
B. For a multi-camera system, it is expected that all video input signals are vertically synchronized, so that when the camera output is converted, the picture distortion will not be caused, but the power supply of each camera in the multi-camera system may be taken from the three-phase power supply. Different phases, even the entire system is not synchronized with the AC power supply, the measures that can be taken at this time are:
The synchronization signal generated by the same external synchronization signal generator is sent to the external synchronization input of each camera to adjust the synchronization.
Adjust the "phase adjustment" potentiometer of each camera, because the vertical synchronization of the camera is in phase with the positive zero crossing of the rising edge of the AC power when it is shipped from the factory, so the use of a phase delay circuit can make each camera have a different phase shift, thus To obtain proper vertical synchronization, the phase adjustment range is 0~360 degrees.
Automatic gain control
All cameras have a video amplifier that amplifies the signal from the CCD to a level that can be used. The amount of amplification is the gain, which is equivalent to having higher sensitivity, which can make it sensitive in low light, but in a bright light environment The amplifier will overload and distort the video signal. To this end, the camera's automatic gain control (AGC) circuit needs to be used to detect the level of the video signal, and the AGC can be switched on and off in a timely manner, so that the camera can work in a larger illumination range, which is the dynamic range, that is, when the illumination is low Automatically increase the sensitivity of the camera, thereby increasing the strength of the image signal to obtain a clear image.
Generally, the AGC working point of the camera is determined by averaging the contents of the entire field of view, but if the field of view contains a very bright background area and a very dark foreground target, the AGC working point determined at this time has It may not be suitable for the foreground target, and background light compensation may improve the display status of the foreground target.
When the background light compensation is on, the camera only averages a sub-region of the entire field of view to determine its AGC operating point. If the foreground target is located in this sub-region, the visibility of the foreground target is expected to improve.
In the CCD camera, the shutter is controlled by the time of charge accumulation on the surface of the optical electronic control image. The electronic shutter controls the accumulation time of the CCD of the camera. When the electronic shutter is closed, the accumulation time of the CCD for the NTSC camera is 1/60 seconds; for the PAL camera, it is 1/50 seconds. When the electronic shutter of the camera is opened, for the NTSC camera, the electronic shutter covers the range from 1/60 second to 1/10000 second in 261 steps; for the PAL type camera, the electronic shutter covers the 1/50 second in 311 steps. To the 1/10000 second range. When the electronic shutter speed increases, the light focused on the CCD decreases within the time allowed for each video field, which will reduce the sensitivity of the camera. However, a higher shutter speed will produce a "pause" for observing moving images. Effect, which will greatly increase the dynamic resolution of the camera.
White balance is only used for color cameras. Its purpose is to realize that the camera image can accurately reflect the scene. There are two methods: manual white balance and automatic white balance.
A, automatic white balance
Continuous mode-At this time, the white balance setting will be continuously adjusted as the color temperature of the scene changes, and the range is 2800~6000K. This method is most suitable for the scene where the color temperature of the scene changes continuously during the shooting, so that the color expression is natural, but for the scene with little or no white, continuous white balance can not produce the best color effect.
Button mode-first point the camera at a white target such as a white wall, white paper, etc., and then manually switch the automatic mode switch to the set position, keep it in this position for a few seconds or until the image appears white, the white balance is executed After that, turn the automatic mode switch back to the manual position to lock the white balance setting. At this time, the white balance setting will be kept in the camera's memory until it is changed again. Its range is 2300~10000K. During this period, even This setting will not be lost when the camera is powered off. It is the most accurate and reliable to set the white balance with the button, which is suitable for most applications.
B. Manual white balance
Turning on manual white balance will turn off automatic white balance. At this time, there are up to 107 levels for adjusting the red or blue status of the image, such as increasing or decreasing the red level and increasing or decreasing the blue level. In addition to times, some cameras also have commands to fix white balance at 3200K (incandescent lamp level) and 5500K (daylight level).
For most applications, there is no need to adjust the color of the camera. If you need to adjust it, you need to carefully adjust it to avoid affecting other colors. The adjustable color methods are:
Red-yellow color increases, at this time move red to magenta one step.
Red-yellow color decreases, at this time move red to yellow one step.
Blue-yellow color increases, at this time move blue to cyan blue one step.
Blue-yellow color is reduced, at this time move blue to magenta one step.
● Pixel: This is a common parameter. In the case that the chip is determined, the higher the pixel, the lower the sensitivity, and the relationship between the two is inversely proportional.
●Dynamic range: Actually this parameter depends on 2 other parameters. Dynamic range = 20Xlog10 (full well electrons/total noise) The higher the parameter, the higher the sensitivity of the CCD.
●Full-well electrons: From the calculation of the dynamic range, the larger the number of full-well electrons, the better.
●Noise: Simple understanding is noisy signal. There are read noise and dark noise. The extra noise when the readout noise camera electronic components process the image is related to the electronic efficiency.
●Cooling: When the CCD is working, the temperature will rise, which will produce noise, especially for long exposures (if fluorescent shooting and other situations require longer exposure time), if the temperature is lowered, this type of noise can be reduced, so everyone sees There is a cold CCD. There are many cooling methods, such as installing fans, semiconductor cooling, water cycle cooling, and liquid nitrogen cooling. The lower the cooling, the better the noise reduction, but the higher the cost.
●Gray scale: generally how many bits are written, this value is better, so that it will be helpful in the shooting of pictures with many levels or indistinguishable, the common is blood smear shooting in the hospital hematology department: red blood cells are very It's thin and many. When you look under the mirror, you often find that there is a lot of overlap. The human eye is better to distinguish the overlapping parts. However, if you change to the CCD, it basically needs more than 12bit, preferably 14bit. For gray scale analysis or fluorescence quantitative analysis, the gray scale is still high.
● Chip size: Because of the inverse relationship between pixels and sensitivity, the chip size is naturally larger.
●Speed: This is naturally the faster the better, but pay attention to the distinction: the speed is divided into readout speed, preview speed, and collection speed; high readout speed is not necessarily preview, collection is fast, because it is also affected by the back interface, computer, etc. The impact of the preview speed is affected by the resolution, and the acquisition speed is relatively better, because his changes are basically only affected by the configuration of the computer.
●Interface: The most commonly used is the USB interface, followed by 1394, and the serial port.
●binning: This is a common method to improve CCD preview and acquisition. The higher the binning supported, the faster the speed can be increased, but the resolution will be sacrificed-in fact, it is to calculate a few pixels as a pixel, such as 2X2 is to treat 4 pixels as one pixel;
●Exposure time: the longer the support time, the better it will be when shooting low light; as for the minimum exposure time, in principle, it can reflect the sensitivity of the CCD sideways, but there are many conditions that need to be referenced.
● GAIN: A signal amplification parameter. The larger the GAIN, the shorter the exposure time required, but the corresponding noise will also increase.
1. What is a CCD camera?
CCD is the abbreviation of Charge Coupled Device, it is a semiconductor imaging device, so it has the advantages of high sensitivity, anti-glare, small distortion, small size, long life, anti-vibration and so on.
2. How the CCD camera works
The image of the subject is focused on the CCD chip through the lens. The CCD accumulates a corresponding proportion of charge according to the intensity of the light. The charge accumulated in each pixel moves outward point by point under the control of the video timing, and is formed after filtering and amplification processing. Video signal output. Connect the video signal to the video input terminal of the monitor or TV to see the same video image as the original image.
3. Choice of resolution
The index for evaluating the resolution of the camera is the horizontal resolution, whose unit is line pairs, that is, the number of black and white line pairs that can be resolved after imaging. The resolution of commonly used black and white cameras is generally 380-600, and the color is 380-480. The larger the value, the clearer the imaging. For general surveillance occasions, a black-and-white camera with about 400 lines can meet the requirements. For special occasions such as medical treatment and image processing, a 600-line camera can get clearer images.
4. Imaging sensitivity
Usually the minimum environmental illumination requirement is used to indicate the camera sensitivity. The sensitivity of the black and white camera is about 0.02-0.5 Lux (lux), and the color camera is mostly above 1 Lux. The 0.1Lux camera is used for ordinary surveillance occasions; at night or when the ambient light is weak, it is recommended to use a 0.02Lux camera. When used with a near-infrared light, a low-illumination camera must also be used. In addition, the sensitivity of the camera is also related to the lens, 0.97Lux/F0.75 is equivalent to 2.5Lux/F1.2 is equivalent to 3.4Lux/F1. Reference ambient illumination: 100000Lux under the summer sun and cloudy outdoor 10000Lux TV studio 1000Lux from 60W table lamp 60cm Desktop 300Lux Indoor Fluorescent Lamp 100Lux Dusk Indoor 10Lux 20cm Candlelight 10-15Lux Night Street Lamp 0.1Lux
5. Electronic shutter
The electronic shutter time is between 1/50-1/100000 seconds. The electronic shutter of the camera is generally set to the automatic electronic shutter mode, which can automatically adjust the shutter time according to the brightness of the environment to obtain a clear image. Some cameras allow users to manually adjust the shutter time to suit certain special applications.
6. External synchronization and external trigger
External synchronization refers to the use of the same synchronization signal between different video devices to ensure the synchronization of the video signal. It can ensure that the video signals output by different devices have the same frame and line start and end time. In order to achieve external synchronization, a composite sync signal (C-sync) or composite video signal needs to be input to the camera. External synchronization does not guarantee that users get a complete continuous frame of images from a specified time. To achieve this function, you must use some special cameras with external trigger functions.
7. Spectral response characteristics
The CCD device is made of silicon material, which is more sensitive to near infrared, and the spectral response can be extended to about 1.0um. The peak of its response is green light (550nm), and the distribution curve is shown on the right. In the case of covert surveillance at night, you can use near-infrared lights to illuminate the environment. The human eye cannot see the environment clearly, but it can clearly image on the monitor. Because the CCD sensor has a layer of transparent electrodes that absorb ultraviolet light, the CCD is not sensitive to ultraviolet light. The imaging unit of the color camera has red, green and blue filter bars, so the color camera is not sensitive to infrared and ultraviolet.
8. CCD chip size
The imaging size of the CCD is usually 1/2", 1/3", etc., the smaller the imaging size, the smaller the size of the camera. Under the same optical lens, the larger the imaging size, the larger the angle of view. Chip specifications Image size (width X height) diagonal 1/2 6.4x4.8mm 8mm 1/3 4.8x3.6mm 6mm
9. Pixel: This is a common parameter. In the case where the chip is determined, the higher the pixel, the lower the sensitivity, and the relationship between the two is inversely proportional, so the higher the pixel, the better. If the pixel is enough, you should give priority to ensuring the sensitivity.
The details were not clearly written. First of all, the handling of light is not clearly written, including what kind of lens is a micro lens (convex lens?), and the light converges to pixels? Secondly, the description of color separation filters is more obscure. If it is RGB, are there three color filters or one color filter to control the color of time to handle the brightness of different colors? If it is three color filters, it will definitely be divided into three layers, each layer must be added with a pixel, this scheme can basically be rejected. Therefore, it should be time-sharing to control the color filter. Such a consequence is that the processing speed is much slower than that of 3CC (because the color filter is controlled). Another difference is to consider the color filter effect by controlling the color filter. Whether there is a static color filter (temporarily called a lens filter, which cannot be controlled by dynamic color filtering), the color filter effect is good, this may be the difference in imaging of the 3CCD single CCD. Finally, there is no explanation on how to compare the pixel calculation of the 3CCD with the single CCD. The principle of 3CCD is to split the light through a triangular prism (RGB), and then project on different CCDs (personally think that the CCD used by 3CCD and single CCD should not be the same, 3CCD may use no color filter, of course, you can also use and single CCD There is also a color filter, so the cost may increase), such a consequence is that a CCD pixel determines the pixels of the entire shooting screen, rather than a single CCD×3. In this way, Panasonic's 3CCD actually sacrifices picture pixels in exchange for color reproduction. The pixels can of course be supplemented by mathematical interpolation, so the picture pixels seen from the outside are the same as other single CCD picture pixels. If you zoom in, the 3CCD picture may be more blurred than the single CCD (same pixel) , I don't know if anyone has tested it yet.
About CCD format: CCD file is the text generated by CloneCD, which records the attributes of CD/DVD disc image. The CCD file is only a description file of the CD image file, so it must be used in conjunction with the CD image, such as IMG+CCD+SUB.
It can be opened using WinMount.
FPGA Virtex-5 FXT Family 65nm Technology 1V 1738-Pin FCBGA
CPLD CoolRunner -II Family 12K Gates 512 Macro Cells 128MHz 0.18um Technology 1.8V 208-Pin PQFP
CPLD CoolRunner -II Family 12K Gates 512 Macro Cells 179MHz 0.18um Technology 1.8V 324-Pin FBGA
FPGA Spartan-XL Family 20K Gates 950 Cells 217MHz 3.3V 208-Pin HSPQFP EP
FPGA Spartan-3A DSP Family 3.4M Gates 53712 Cells 667MHz 90nm Technology 1.2V 676-Pin FBGA