Photosensitive coupling assembly

Integrated circuit

open 3 entries with the same name

synonym CCD (Charge coupled element) generally refers to the light-sensitive coupling module

This entry is made by Compilation and application of scientific encyclopedia entries of "Science Popularization China" to examine.

Photosensitive coupling module is also called charge coupled device (English: Charge-coupled Device ， abbreviation ： CCD ）, is a kind of Integrated circuit , there are many neatly arranged capacitance , can sense light and convert video into digital signal. Through the control of external circuit, each small capacitor can transfer its charge to its adjacent capacitor. CCD is widely used in digital photography, astronomy, especially in optical telemetry, optical and spectrum telescopes, and High-speed photography Technology such as Lucky imaging 。

Chinese name: Photosensitive coupling assembly
Foreign name: Charge-coupled Device

Discipline: Optical remote sensing
Abbreviations: CCD

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History

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CCD was established in 1969 by the United States Bell Laboratories Of Willard Boyle (Willard Sterling Boyle) and George Elwood Smith. At that time, Bell Laboratories was developing visual telephone and semiconductor Bubble memory. After combining these two new technologies, Boyle and Smith came up with a device named Charge "Bubble" Devices. The characteristic of this device is that it can be transmitted along the surface of a semiconductor charge , and tried to use it as a memory device. At that time register Input memory by "injecting" charge. But then I found that photoelectric effect It can generate electric charges on the surface of such components to form digital images.

In 1971, researchers at Bell Laboratories were able to capture video with simple linear equipment, and CCD was born. Several companies, including Fairchild Semiconductor Radio America and Texas Instruments 。 Among them, Fairchild Semiconductor took the lead in launching its products. In 1974, it published 500 unit linear devices and 100x100 pixel planar devices.

In January 2006, Boyle and Smith were awarded the Charles Stark Draper Medal by the Institute of Electrical and Electronic Engineers in recognition of their contributions to the development of CCD. In October 2009, they won Nobel Prize in Physics 。^[1]

principle

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In grid electrode (G), positive voltage will produce potential well (yellow), and collect the charge packet (electrons, blue) into it. Just apply positive voltages in the correct order to conduct the charge packet.

In a CCD used for photosensitivity, there is a photosensitive area (silicon epitaxial layer), and shift register Made sensing area (CCD in narrow sense).

The image is projected on a row of capacitors (photosensitive area) through the lens, causing each capacitor to accumulate a certain charge, and the amount of charge is proportional to the incident light intensity there. One dimensional capacitance array for line scanning camera can scan a single layer of capacitance each time; The two-dimensional capacitive array used for cameras and general cameras can scan images projected on the focal plane. Once the capacitor array is exposed, a control loop will enable each capacitor to transfer its own charge to the next adjacent capacitor (sensing area). The charge in the last capacitor in the array will be transferred to a Charge amplifier And is converted into voltage signal. By repeating this process, the control loop can convert the charge in the entire array into a series of voltage signals. stay digital circuit , these signals will be sampling Digital, usually stored; And in Analog circuit They will be processed into a continuous analog signal (for example, the output signal of the charge amplifier is transmitted to a low pass filter ）。^[2]

application

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CCD with lattice arrangement pixels is applied to digital camera 、 optics Scanner And movie camera The photosensitive component of. Its light efficiency can reach 70% (70% of the incident light can be captured), which is superior to the traditional film 2%, so CCD can quickly obtain astronomer Extensive adoption of.

Webcam using CCD（ camera lens ) fax machine Linear CCD used

Video via lens Imaging on capacitance After the array surface, according to the intensity of its brightness, charges of varying intensity are formed on each capacitor unit. The linear CCD used by the fax machine or scanner captures a thin strip of light and shadow at a time, while the flat CCD used by the digital camera or camera captures a whole video at a time, or intercepts a square area from it. Once the exposure action is completed, the control circuit will make the charge on the capacitor unit transfer to the next adjacent unit. When it reaches the last unit on the edge, the electrical signal will be transmitted to the amplifier and converted into potential. This continues until the entire video is converted into potential, sampled and digitized, and stored in memory. Stored videos can be sent to printer 、 storage device or monitor 。 At the same time, the frozen CCD was also widely used in astronomical photography and various night vision equipment in the early 1990s, and various large observatories have also continued to develop high image number CCD to take extremely high resolution photos of celestial bodies.

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 CCD match celestial bodies The running direction is consistent and the speed is synchronized to CCD guide star Not only can the telescope effectively correct the tracking error, but also can the telescope record a larger field of view than the original.

Most ordinary CCD can sense infrared Therefore, infrared video, night vision equipment, zero illuminance (or near zero illuminance) camera/camera, etc. are derived. Because objects at room temperature will have infrared Blackbody radiation In order to reduce infrared interference, the astronomical CCD is usually Liquid nitrogen Or semiconductor cooling. The sensitivity of CCD to infrared causes another effect. If various digital cameras or video recorders equipped with CCD are not equipped with infrared filters, it is easy to capture the infrared emitted by the remote controller. Lowering the temperature can reduce the dark current on the capacitor array, improve the CCD's sensitivity to low illumination, and even improve the sensitivity to ultraviolet and visible light (increase the signal-to-noise ratio).

temperature Noise 、 dark current (dark current) and cosmic radiation will affect the pixels on the CCD surface. Astronomers use the shutter opening and closing to expose the CCD multiple times, and take the average value to mitigate the interference effect. To remove background noise, first take the average value of the video signal when the shutter is closed, that is, "dark frame". Then open the shutter, get the video, subtract the value of the dark frame, and filter out the system noise (dark spots, bright spots, etc.) to get clearer details.

The cooling CCD camera used for astronomical photography must be fixed at the imaging position with a ring to prevent the impact of external light or vibration; At the same time, because most video platforms are inherently cumbersome and need to shoot videos of galaxies, nebulae and other dim objects, astronomers use the "automatic star guide" technology. Most automatic star guidance systems use additional CCD with different axes to monitor any video offset, however, some systems connect the main mirror to the CCD camera used for shooting. Add part of the starlight in the main mirror to another CCD guide star device in the camera with optical equipment, which can quickly detect the tiny error when tracking celestial bodies, and automatically adjust the drive motor To correct the error without additional guide star equipment.^[2]

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