CCD structure includes photodiode, parallel signal register, parallel signal register, signal amplifier, digital-to-analog converter and other items, which will be introduced separately below. 1 .photodiode 2. Shift register: used to temporarily store the charge generated after exposure. 3. Transfer register: used to temporarily store the analog signal of the parallel accumulator and transfer and amplify the charge. 4. Signal amplifier: used to amplify weak electrical signals. 5. Digital-to-analog converter: converts the amplified electrical signal into a digital signal. The working principle of CCD consists of three layers: microlens, dichroic filter and photosensitive layer, which will be introduced separately below. 1. microlens microlens is the first layer of CCD. We know that the key of digital camera imaging lies in its photosensitive layer. In order to expand the lighting rate of CCD, it is necessary to expand the light receiving area of a single pixel. However, the method of improving the lighting rate is also easy to reduce the image quality. This layer of "microlens" 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 microlens. 2. The dichroic filter is the second layer of CCD. At present, there are two color separation methods, one is RGB primary color separation method, the other is CMYK complementary color separation method. These two methods have their own advantages and disadvantages. First of all, let's understand the concepts of two color separation methods. RGB is a method for separating three primary colors. Almost all the colors that human glasses can recognize can be composed of red, green and blue. The three letters of RGB are red, green and blue respectively, which shows that RGB color separation is formed by adjusting the colors of these three channels. Let's talk about CMYK, which is composed of four channels of colors, namely 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 primary color CCD is sharp image quality and true color, but the disadvantage is noise. Therefore, we can notice that the ISO sensitivity of digital cameras that generally use primary color CCD will not exceed 400. In contrast, complementary color CCD has a Y-yellow color filter, which pays more attention to color resolution, but sacrifices the resolution of some images. On the ISO value, complementary color CCD can tolerate higher sensitivity, which can generally be set above 800. 3. The photosensitive layer is the third layer of CCD, which is mainly responsible for converting the light source passing through the color filter into an electrical signal and transmitting the signal to the image processing chip to restore the image. CCD chip, like human retina, is the core of the camera. At present, China has no manufacturing capacity. Most cameras on the market use chips produced by Japanese companies such as Sony, Sharp, Panasonic and Fuji. Now South Korea's Samsung has the ability to produce, but the quality will be slightly inferior. Due to the different grades produced in chip production and the different ways obtained by various manufacturers, the acquisition effect of CCD is also very different. When buying, you can take the following methods to detect: turn on the power supply, connect the video cable to the display, close the lens aperture, and see if there are bright spots when the image is completely black, and whether the snow on the screen is big or not. These are the simplest and most direct methods to detect CCD chips, and no other special instruments are needed. Then you can open the aperture and look at the still life. If it's a color camera, you'd better take a brightly colored object to see if the image on the display is color cast, distorted, smooth or gray. Good CCD can restore the color of the scene well and make the object look clear and natural; However, the image of defective products will have a color cast, and even if it faces a blank sheet of paper, the image will display blue or red. Due to the dust in the production workshop, there will be impurities on the target surface of individual CCD. In general, impurities will not affect the image, but in low light or micrography, fine dust will also cause adverse consequences. If it is used in this kind of work, it must be carefully selected.