Lens sensor

When it comes to digital cameras, I have to say that it is the heart of a digital camera - a sensor. Compared with traditional cameras, traditional cameras use "film" as a carrier for recording information, and the "film" of a digital camera is its imaging sensor, which is integrated with the camera and is the heart of the digital camera. Photoreceptors are the core and the most critical technology of digital cameras. The development path of digital cameras can be said to be the development path of photoreceptors. At present, there are two kinds of core imaging components of digital cameras: one is a widely used CCD (charge coupled) element; the other is a CMOS (complementary metal oxide conductor) device.

Photosensitive element working principle Charge couple device Image sensor CCD (Charge Coupled Device), which is made of a high-sensitivity semiconductor material, can convert light into charge, through the analog to digital converter chip into a digital signal, digital signal After being compressed, it is saved by the camera's internal flash memory or built-in hard disk card, so data can be easily transferred to the computer and the image can be modified as needed and imagined by means of computer processing. CCDs consist of many photosensitive units, usually in megapixel units. When the CCD surface is exposed to light, each photosensitive unit will reflect the charge on the component, and the signals generated by all the photosensitive units are added together to form a complete picture.

Compared with conventional negatives, CCDs are closer to the way the human eye works on vision. However, the retina of the human eye is composed of rod cells responsible for light intensity sensing and color-inducing cone cells, which cooperate to form visual induction. After 35 years of development, the CCD has been shaped and its general shape and mode of operation have been finalized. The composition of the CCD is mainly composed of a mosaic-like grid, condenser lenses, and a matrix of electronic circuits padding at the bottom. The companies that currently have the ability to produce CCDs are: SONY, Philps, Kodak, Matsushita, Fuji, and Sharp. Most of them are Japanese manufacturers.

Complementary metal-oxide-semiconductor (CMOS) complementary semiconductors (CMOS), like CCDs, are semiconductors that record light changes in digital cameras. The manufacturing technology of CMOS is no different from general computer chips. It is mainly made of semiconductors made of silicon and germanium, which make it possible to coexist on the CMOS with N (band-electricity) and P (band + electricity) grades. In semiconductors, the current generated by these two complementary effects can be recorded and interpreted by the processing chip as an image. However, the disadvantage of CMOS is that it is prone to noise. This is mainly due to the fact that early designs made CMOS overheated due to current changes when dealing with rapidly changing images.


The difference between the two types of photosensitive elements can be seen from the working principle of the two types of photosensitive elements. The advantage of the CCD is that the image quality is good, but due to the complexity of the manufacturing process, only a few manufacturers can grasp, so the manufacturing cost is high, especially Is a large CCD, the price is very high. At the same time, in the past few years, the CCD has started from 300,000 pixels and has been developed to the current 6 million. The improvement of pixels has reached a limit.

At the same resolution, CMOS is cheaper than CCDs, but CMOS devices produce lower image quality than CCDs. So far, the vast majority of consumer-grade and high-end digital cameras on the market use CCDs as sensors; CMOS sensors are used as low-end products on some cameras. If any camera manufacturer uses a CCD camera Sensors, manufacturers will spare no effort to use it as a selling point to promote, even the title of "digital camera." For a time, whether or not a CCD sensor has become one of the criteria for judging the quality of digital cameras.

One of the advantages of the CMOS image sensor is that the power consumption is lower than that of the CCD. The CCD provides excellent image quality and the cost is higher power consumption. In order to make the charge transmission smooth and reduce the noise, the transmission effect needs to be improved by the high voltage difference. . However, the CMOS image sensor converts the charge of each pixel into a voltage, which is amplified before reading, and can be driven with a 3.3V power supply. The power consumption is lower than that of the CCD. Another advantage of the CMOS image sensor is its high integration with the peripheral circuits, which can integrate the ADC and the signal processor to greatly reduce the size. For example, a CMOS image sensor requires only one set of power sources, and a CCD requires three or four. In the group power supply, since the process of the ADC and the signal processor is different from that of the CCD, it is difficult to reduce the size of the CCD kit. However, the primary problem to be solved by CMOS image sensors is to reduce noise generation. Whether CMOS image sensors can change the fate that has been suppressed by CCD for a long time and the development of future technologies is an important key.

Factors Affecting Photosensitive Components For digital cameras, there are two main factors that affect imaging of image sensors: First, the area of ​​the sensor, and second, the color depth of the sensor.

The larger the area of ​​the photosensitive element, the greater the image size. Under the same conditions, more details of the image can be recorded, and the interference between the pixels is also small, and the imaging quality is better. However, with the development of digital cameras in the direction of compact fashion, the area of ​​photosensitive elements can only be smaller and smaller.

In addition to the area, the photosensitive element has an important indicator, namely the color depth, which is the color bit, which is how many bits of binary numbers are used to record the three primary colors. Non-professional digital cameras generally have 24-bit sensing elements, high-end point sampling is 30 bits, and recording time is still 24 bits, professional digital camera imaging devices are at least 36, it is said that there have been 48-bit CCD. For 24-bit devices, the light-sensing unit can record a maximum of 2^8 = 256 levels of light intensity. Each primary color is represented by an 8-bit binary number. The maximum recordable color is 256x256x256 about 16,77. Ten thousand kinds. For a 36-bit device, the light-sensing unit can record a maximum of 2^12=4096 levels of light brightness. Each primary color is represented by a 12-bit binary number. The maximum recordable color is 4096x4096x4096, which is about 6.87 billion kinds. . For example, if the brightness of the brightest part of a subject is 400 times the brightness of the darkest part, if you use a digital camera that uses a 24-bit sensor, if you press the low-light part of the exposure, then the brightness is higher than 256 spare parts, all overexposed, level loss, the formation of bright spots, if you press the highlights to exposure, then a certain area below the brightness of all underexposure, if you use a professional digital camera using 36 sensor, it will not There is such a problem.

The development of the photosensitive element CCD was developed in 1969 by Bell Labs in the United States. In the 1980s, CCD image sensors, despite their flaws, finally overcame the difficulties due to continuous research, and manufactured high-resolution and high-quality CCDs in the latter half of the 1980s. In the 1990s, a megapixel high-resolution CCD was produced. At this time, the development of the CCD was even more rapid. It has been more than 20 years since the development of the CCD. After entering the mid-1990s, CCD technology has developed rapidly. At the same time, the unit area of ​​the CCD has become smaller and smaller. However, in order to improve the image quality of the image while reducing the CCD area, SONY and SUPER HAD CCD were developed in 1989. This new photosensitive element relies on the magnification of the internal amplifier of the CCD module when the CCD area is reduced. Improve image quality. Later appeared the NEW STRUCTURE CCD, EXVIEW HAD CCD, four-color filter technology (for SONY F828 applications). The Fuji digital camera uses Super CCD (Super CCD) and Super CCD SR.

For CMOS, with the ease of mass production, and the speed and low cost, it will be the development direction of the key components of digital cameras. At present, with the continuous efforts of companies such as CANON, new CMOS devices are continuously being developed and high dynamic range CMOS devices have emerged. This technology eliminates the need for shutter, aperture, automatic gain control, and gamma correction to bring it closer CCD imaging quality. In addition, due to the inherent plasticity of CMOS, it is possible to make large-sized CMOS photosensors with high pixels without increasing the cost. Compared with the stagnation of the CCD, CMOS has shown its vigorous vitality as a new thing. As a core component of digital cameras, CMOS sensors have a tendency to gradually replace CCD sensors and hopefully become mainstream sensors in the near future.