How many kinds of camera sensors are there?

According to the types of photosensitive devices, most of the lenses used by cameras on the market are CCD and CMOS. Among them, CCD (Charge Coupled Device) is more used as a high-end technical component for camera shooting and image scanning, while CMOS (Complementary Metal Oxide Semiconductor) is mostly used in some low-end video products.

Most of the digital cameras sold in the market are CMOS cameras. Advanced image control technologies, such as automatic gain enhancement technology of image light source, automatic brightness and white balance control technology, color saturation, contrast, edge enhancement and gamma correction, can achieve the same effect as CCD cameras. Limited by the market situation and market development, there are only a few manufacturers who use CCD image sensors for cameras, mainly because of the high cost of using CCD image sensors.

Extended data

Image sensor The image sensor uses the photoelectric conversion function of photoelectric devices. The light image on the photosensitive surface is converted into an electrical signal proportional to the light image. Compared with the photosensitive elements of "point" light sources such as photodiodes and phototransistors, the image sensor is a functional device, which divides the light image on the light receiving surface into many small units and converts it into usable electrical signals. Image sensors are divided into photoconductive camera tubes and solid-state image sensors. Compared with photoconductive camera tube, solid-state image sensor has the characteristics of small volume, light weight, high integration, high resolution, low power consumption, long life and low price. So it is widely used in all walks of life.

Charge coupled device

CCD is a high-end technical component used in photography, while CMOS is used for low-quality products. Its advantages are lower manufacturing cost and much lower power consumption than CCD, which is why many products with USB interface on the market do not need external power supply and are cheap. Although there are great differences in technology, the performance gap between CCD and CMOS is not very big, but CMOS cameras have higher requirements for light sources, but this problem has been basically solved. The dimensions of CCD elements are mostly 1/3 inches or 1/4 inches. Under the same resolution, it is better to choose a larger element size. An image sensor is also called a photosensitive element.

App application

Image sensor? Or photosensitive element, is a device that converts optical images into electronic signals. It is widely used in digital cameras and other electronic optical equipment. Early image sensors used analog signals, such as video cameras. With the rapid development of digital technology, semiconductor manufacturing technology and network, the market and industry are facing the era of great integration of video, audio-visual and communication across various platforms, which depicts the beautiful scenery of human daily life in the future.

With its application in daily life, it is undoubtedly a digital camera product, and its development speed can be described by rapid changes. In just a few years, digital cameras have developed from hundreds of thousands of pixels to 4 million, 5 million pixels or even higher. Not only in developed European and American countries, but also in developing China, the digital camera market is growing at an alarming rate. Therefore, its key component, image sensor products, has become the focus of current and future industry attention, attracting the investment of many manufacturers.

According to product categories, image sensor products are mainly divided into CCD, CMOS and CIS sensors. This paper will mainly introduce the technology and industrial development status of CCD and CMOS sensors.

history

Photosensitive device is the core component of industrial camera, and there are two kinds of image sensors: CMOS and CCD. The unique technology of CCD has the advantages of good low illumination effect, high signal-to-noise ratio, strong transparency and good color reproduction ability, and is widely used in high-end fields such as transportation and medical care. Because of its imaging advantages, it will continue to be used for a long time, but at the same time its high cost and high power consumption also restrict its market development space.

CCD and CMOS have their own advantages in different application scenarios, but with the continuous improvement of CMOS technology and technology and the continuous decline of high-end CMOS prices, I believe that CMOS will occupy an increasingly important position in the development of high-definition cameras in the security industry in the future.

CCD (Charge Coupled Device) was successfully developed in Bell Laboratories on 1969, and then mass-produced by Japanese companies and other companies. Its development history has been nearly 30 years. CCD can be divided into two types: line type and plane type, in which line type is used for image scanners and fax machines, and plane type is mainly used for digital cameras (DSC), video cameras, surveillance cameras and other image input products.

trait

It is generally believed that CCD sensor has the following advantages:

high-resolution

(High resolution): The pixel size is micron, which can sense and identify fine objects and improve image quality. From 1 inch, 1/2 inch, 2/3 inch, 1/4 inch to 1/9 inch, the number of pixels increased from 1 10,000 to 4-5 million pixels;

low noise

(Low noise) High sensitivity: CCD has extremely low readout noise and dark current noise, thus improving the signal-to-noise ratio (SNR). At the same time, it has high sensitivity, and can detect the incident light with extremely low luminosity, and its signal will not be covered up, so that the application of CCD is less restricted by the weather;

Wide Dynamic Range

(High dynamic range): detect and distinguish strong light and weak light at the same time, improve the application range of the system environment, and will not cause signal contrast due to large brightness difference.

Good linear characteristic curve

Linearity: the intensity of incident light source has a good direct ratio with the size of output signal, which will not lose object information and reduce the cost of signal compensation processing;

High quantum efficiency: it can record very weak incident light, and even detect distant scenes in the dark night if it is matched with an image intensifier and a projector;

Large area photosensitive

(Large field of view): A large area CCD chip can be manufactured by using semiconductor technology. A 35mm CCD with the same size as the traditional negative has been applied to digital cameras, becoming a key component to replace professional and advantageous optical cameras.

Wide spectral response: it can detect light in a wide wavelength range, increase the flexibility of the system and expand the application field of the system;

Low image distortion

(Low image distortion): With CCD sensor, the image processing will not be distorted and can faithfully reflect the original object information;

Small size, light weight

CCD has the characteristics of small size and light weight, and can be easily installed on artificial satellites and various navigation systems.

low power consumption

Not affected by strong electromagnetic field;

Good charge transfer efficiency: This efficiency coefficient affects the signal-to-noise ratio and resolution. If the charge transfer efficiency is not good, the image will become blurred;

It can be mass-produced, with stable quality, firmness, no aging, convenient use and easy maintenance.

According to the In-Stat 2006 54 38+0 global image sensor research report, it is pointed out that the top seven manufacturers in CCD industry are all Japanese manufacturers, accounting for 98.5% of the global market share. In terms of technological development, Sony, Philips and Kodak should be the main manufacturers with characteristics.

Complementary metal oxide semiconductor

trait

CMOS sensor adopts the most commonly used CMOS technology in general semiconductor circuits, which has the characteristics of high integration, low power consumption, high speed and low cost. In recent years, it has developed rapidly in wide dynamic and low illumination. CMOS is a complementary metal oxide semiconductor, which is mainly composed of silicon and germanium. Its basic function is realized by negatively charged and positively charged transistors on CMOS. The current generated by these two complementary effects can be recorded by the processing chip and interpreted as an image.

Among analog cameras and standard definition network cameras, CCD is the most widely used and has occupied a leading position in the market for a long time. CCD is characterized by high sensitivity, but slow response, which is not suitable for high-resolution progressive scanning mode used by high-definition surveillance cameras. Therefore, after entering the era of high-definition surveillance, CMOS is gradually recognized by people, and CMOS photosensitive devices are widely used in high-definition surveillance cameras.

The main advantage of CMOS used in CCD is very power saving. Unlike CCD composed of diodes, CMOS circuits have almost no static power consumption. This makes the power consumption of CMOS only about 1/3 of that of ordinary CCD. The important problem of CMOS is that when dealing with fast-changing images, it is overheated because of too frequent current conversion, so it is not a big problem to suppress dark current well, and it is very easy to appear noise if it is not suppressed well.

720P and 1080P back-illuminated CMOS devices have been developed, and their sensitivity performance is close to that of CCD. Compared with the surface-illuminated CMOS sensor, the back-illuminated CMOS sensor has great advantages in sensitivity (S/N), which significantly improves the shooting effect in low illumination, so the noise can be greatly reduced when shooting in low illumination.

Although the megapixel camera products based on CMOS technology have some shortcomings in low illumination environment and signal noise processing, it will not fundamentally affect its application prospects. In addition, relevant international enterprises are stepping up efforts to solve these two problems. I believe that in the near future, the effect of CMOS will be closer and closer to CCD, and the price of CMOS equipment will be lower than CCD equipment.

It has become an indisputable fact that CMOS is more used in security industry than CCD. Although the resolution of CCD sensor with the same size is better than that of CMOS sensor, if the size limit is not considered, the advantage of CMOS in quantity rate can effectively overcome the difficulty of manufacturing large-size photosensitive elements, so that CMOS will have an advantage in higher resolution. In addition, the response speed of CMOS is faster than that of CCD, which is more suitable for high-definition monitoring of big data.

history

Compared with CCD, CMOS has the advantages of small size, lower power consumption than110 and lower price than CCD 1/3.

Compared with CCD products, CMOS is a standard process, which can make use of existing semiconductor equipment without additional investment equipment, and the quality can be improved with the improvement of semiconductor technology. At the same time, there are many CMOS production lines in global fabs, which will also help to reduce costs in mass production in the future. In addition, the biggest advantage of CMOS sensor is that it has high system integration.

Theoretically, all the functions required by the image sensor, such as vertical displacement, horizontal displacement register, timing control, CDS, ADC? Wait. , can be integrated on a chip, even all chips including back-end chip and Flash RAM can be integrated into a system on chip, thus achieving the purpose of reducing the production cost of the whole machine.

Because of this, there are more manufacturers investing in R&D, including more than 30 in the United States, 7 in Europe, about 8 in Japan, 8 in Korea 1 and 8 in Taiwan Province Province. The leading manufacturer in the world is Agilent (Hewlett-Packard), with a market share of 565,438+0%, ST (Very Large Scale Integrated Circuit Vision) of 65,438+06%, Omni Vision of 65,438+03%, Hyundai of 8% and Photobit of about 5%, with a total market share of 93%.

According to In-Stat statistics, by 2004, the global sales of CMOS sensors are expected to exceed 654.38+0.8 billion US dollars, and CMOS will grow rapidly with a compound annual growth rate of 62%, gradually eroding the application fields of CCD devices. Especially in the rapidly developing mobile phone application field of 20 13, the camera module based on CMOS image sensor will occupy more than 80% of its application market.

market

CMOS image sensor belongs to the new product market, and its market share is not as constant as that of mature industries. For example, in CMOS market, Agilent, OmniVision, STM, and Hyundai are ranked according to the proportion of shipments, with market shares of 24%, 22%, 14%, and 14% respectively, among which STM. However, after only one year of market competition, Agilent and OmniVision still ranked first and second, with their market share increasing to 37.7% and 30.8% respectively, while STM ranked fourth, with its market share dropping to 4.8%.

As for Hyundai, the market share is only 2. 1% after a sharp decline. It is worth mentioning that in 2000, Photobi had a great growth, and its global market share increased rapidly to 13.7%, ranking third in the world. The shipments of these three manufacturers accounted for 82.2% of the global shipments. From this analysis, we can see that the concentration of manufacturers in this industry is quite dense, so observing the dynamics and development of the above three manufacturers, we can see the future development direction of Xu industry and technology.

Agilent's main products are the second generation CIF(352*288)HDCS- 1020 and the second generation VGA(640*480)HDCS-2020, which are mainly used in digital cameras, mobile phones, PDA, PC cameras and other emerging information appliances. In addition, another successful strategy of Agilent in 2000 was to enter the field of optical mouse products through strategic alliance with Logitech and Microsoft, but this is a very low-level CMOS product, and it is not used to capture images.

Therefore, this figure is not included in the global statistics of image sensors, but it shows that Agilent plans to enter optical components based on CMOS technology.

The main products of OmniVision include _CIF(352 x 288), VGA(640 x 480), SVGA(800 x 600) and SXGA( 1280 x 1024). The CMOS image sensor with 6.5438+0.3 million pixels developed by Omnivision is being widely used in digital cameras. The industry generally believes that one million pixels is the watershed of using CMOS and CCD. The successful entry of CMOS into this market shows that the development of CMOS technology has penetrated into the market and may replace CCD as the application of low-end image products in the future.

The CMOS sensor of CIF(352 x 288) level developed by OmniVision in May 20065438+0 is characterized by low power consumption. Its target market is mobile phones, and its product development strategy coincides with that of major research institutions. In the mobile phone market, the camera module of CMOS module has become the most widely used product in mobile communication.

Photobit was a great success in 2000. In 200 1 year, Photobit took the lead in developing the CMOS image sensor of PB-0330 product model. This product uses a single-chip logic-digital converter, which is the second generation of 1/4-inch VGA(640 x 480), and also introduces the CMOS image sense of Pb-01/product model.

Photobit launched these two products mainly for digital cameras and PC cameras, which are different from OmniVision CIF(352 x 288) in the mobile phone market. It has introduced two image sensors with different resolutions, CIF(352 x 288) and VGA(640 x 480), and its marketing scope is intended to cover the low-end and high-end markets.

develop

20 13, the industry has developed a new technology of CMOS image sensor-C3D. The biggest feature of C3D technology is the uniformity of pixel reaction. C3D technology redefines the performance of imager (including the overall performance of the system), and improves the standard performance of CMOS image sensor in terms of uniformity and dark current.

At the beginning of 20 14, American company Foveon publicly demonstrated its newly developed Foveon X3 technology, which immediately attracted great attention from the industry. Foveon X3 is the first image sensor array in the world that can capture all colors on one pixel. Traditional photoelectric coupling devices can only sense light intensity, but can't sense color information. It needs to perceive color information through a color filter, which we call Bayer color filter. On the other hand, Foveon X3 senses color at different depths of a pixel, with the outermost layer sensing blue, the second layer sensing green and the third layer sensing red.

It is based on the absorption effect of silicon on light with different wavelengths to realize that a pixel perceives all color information. CMOS image sensors have adopted this technology, and its application product is "Sigma SD9" digital camera.

This innovative technology can provide clearer images and better colors. Compared with the previous image sensor, X3 is the first sensor to detect color through the built-in silicon photoelectric sensor. Of Foveon's technology has made a major breakthrough in the traditional semiconductor photosensitive technology, and also has the effect of subverting the traditional technology. I believe Foveon X3 will have a bright future.

In terms of high-resolution pixel products, a few days ago, Taiwan Province Ruishi Technology has led the industry in mass production of 265,438+megapixel CMOS image sensors. American companies cooperated with Taiwan Province Optical Lens Factory to launch this module of CMOS sensor combined lens in the third quarter, and CMOS applications have begun to be applied in 2 megapixel digital camera products.

contrast

CCD provides good image quality, anti-noise ability and camera design flexibility. Although the volume and complexity of the system are increased due to the addition of external circuits, the circuit design can be more flexible and improve some special performance of CCD camera as much as possible. CCD is more suitable for applications that require very high camera performance but not strict cost control, such as astronomy, high-definition medical X-ray images, and other scientific applications that require long-term exposure and strict image noise.

CMOS is an image sensor which can be produced by modern large-scale semiconductor integrated circuit production technology, and has the characteristics of high yield, high integration, low power consumption and low price. CMOS technology is a technology that many image sensor semiconductor research and development enterprises in the world try to replace CCD. After years of efforts, CMOS, as an image sensor, has overcome many shortcomings in the early stage and developed to a level that can compete with CCD technology in image quality.

The level of CMOS makes it more suitable for applications requiring small space, small volume and low power consumption, but not particularly demanding image noise and quality. For example, most industrial inspection applications with auxiliary lighting, security applications and most consumer commercial digital camera applications.

technical parameter

Understanding the imaging principle and main parameters of CCD and CMOS chips is very important for product selection. Similarly, the performance of cameras made of the same chip through different designs may also be different.

The main parameters of CCD and CMOS are as follows:

1, pixel size?

Pixel size refers to the actual physical size of each pixel on the chip pixel array, and the usual sizes are 14um, 10um, 9um, 7um, 6.45um, 3.75um, etc. The pixel size reflects the chip's response to light to some extent. The larger the pixel size, the more photons can be received and the more charges can be generated under the same lighting conditions and exposure time. For low light imaging, pixel size is a representation of chip sensitivity.

2. sensitive?

Sensitivity is one of the important parameters of the chip, which has two physical meanings. One refers to the photoelectric conversion ability of optical devices, which means the same as responsivity. That is, the sensitivity of the chip refers to the output signal voltage (current) per unit exposure within a certain spectral range, and the unit can be Na 'an/Le Kaessner/Lux, Volt/Watt (V/W), Volt/Lux and Volt/Lumen (V/lm). The other refers to the radiation power (or illuminance) to the ground that the equipment can perceive, which has the same meaning as the detection rate. Units can be expressed in watts (W) or lux.

3. Bad score?

Due to the limitation of manufacturing process, it is almost impossible for all pixels of a megapixel sensor to be good. The number of bad pixels refers to the number of bad pixels in the chip (pixels that cannot be imaged effectively or whose corresponding inconsistency is greater than the allowable range of parameters), which is an important parameter to measure the quality of the chip.

4. Spectral sensitivity

Spectral response refers to the chip's response ability to light with different light wavelengths, which is usually given by spectral response curve.

Judging from the technical development trend of products, miniaturization and high pixel of both CCD and CMOS are still the active research and development goals of the industry. Because of the small pixel size, image products have higher resolution, better definition, smaller size and wider application.

Judging from the resolution of the above two kinds of image sensors, in the next few years, with 1.3 million pixels as the boundary, CCD will still be the mainstream in the above application fields, and CMOS sensors will be the mainstream in the following products. According to industry analysis, from the end of 20 14 to the beginning of 20 15, there will be 3 million pixel CMOS on the market. It is predicted that CMOS market will surpass CCD in 2004 -2005.

Development situation

Now the video scale of the image sensor is given. With the high-definition (HD) resolution of 1080p, camera design is developing towards using smaller optical formats, resulting in the need for smaller pixel structures to reduce the overall system cost without affecting image performance or sensitivity.

Because of its high sensitivity and low noise, CCD image sensor has gradually become the mainstream of image sensor. However, due to technical reasons, the sensing element and signal processing circuit cannot be integrated on the same chip, which leads to the large size and high power consumption of the camera assembled by CCD image sensor.

CMOS image sensor is unique in the image sensor market because of its small size and low power consumption. However, CMOS image sensors in the market did not get rid of the shortcomings of low illumination sensitivity and low image resolution at first, and the image quality could not be compared with CCD image sensors.

If the illumination sensitivity of CMOS image sensor is further improved by 5 times, reaching 10 times, and the noise is further reduced, the image quality of CMOS image sensor can reach or slightly exceed that of CCD image sensor, while maintaining the advantages of small size, light weight, low power consumption, high integration and low price. In this way, CMOS image sensor will replace CCD image sensor and play a better role.

Due to the application of CMOS image sensor, the development of new generation image system has been greatly developed, and with the formation of economic scale, its production cost has also been reduced. At present, the image quality of CMOS image sensor can be comparable to that of CCD image sensor, which is mainly due to the improvement of image sensor chip design and the addition of new functions in sub-micron and deep sub-micron design.

In fact, more accurately, CMOS image sensor should be an image system. A typical CMOS image sensor usually includes an image sensor core (which multiplexes discrete signal levels into a single output, similar to a CCD image sensor), all sequential logic, a single clock and programmable functions in the chip, such as gain adjustment, integration time, window and analog-to-digital converter.

In fact, designers buy CMOS image sensors and get a whole system including image array logic registers, memories, timing pulse generators and converters. Compared with the traditional CCD image system, integrating the whole image system on one chip not only reduces power consumption, but also has the advantages of lighter weight, less occupied space and lower overall price.

Reference source: Baidu Encyclopedia-Image Sensor