Video surveillance high-definition imaging chip development prospects

With the rapid development of digital technology, semiconductor manufacturing technology and networks, the digital product market is growing at an alarming rate. The image sensor, which is a key component of video and audio/video products, has become the focus of current and future industries. . The image sensor mainly includes CCD and CMOS chips. In our current field of high-definition security video surveillance, CMOS chip products have been widely applied to a wide variety of products.

Development and Application of Image Sensors

The eye is the source of human visual images, and the image sensor is the image capture device of the video capture device. There are generally two types of image sensors classified by morphology: linear image sensors and surface image sensors. Linear image sensors are used in scanners, copiers, and fax machines. The surface image sensors are widely used in security surveillance cameras, mobile phone cameras, car reversing video cameras, and tablet computers.

We just mentioned that there are two types of image sensors, CCD and CMOS. In the early days, we generally believed that CCD sensors were used in devices with excellent image quality, while CMOS sensors were used in low-cost products. However, the new CMOS chip technology has overcome the technical weaknesses of earlier CMOS sensors, and the sensor design has improved low-light performance, exposure mode, and the like compared to the old products. Take the current popular back-illuminated CMOS sensor, in the traditional CMOS image sensor, the photodiode is located behind the circuit transistor, the light will pass through the circuit and the transistor between the microlens and the photodiode, then the amount of light will be blocked. affected.

The back-illuminated CMOS sensor has been optimized in the internal structure of the image sensor original, it will turn the original photosensitive layer direction, so that the light from the image sensor than the traditional CMOS sensor in the photosensitivity of a qualitative leap in low light conditions, High-resolution cameras with back-illuminated CMOS sensors have greatly improved performance in terms of focusing capabilities, image quality performance, and image noise control.

Back-illuminated CMOS image sensors have better high-sensitivity and noise control performance in addition to excellent low-light performance. In other words, after the increase of ISO, 3DDNR technology with cash, the noise will be much less than CCD. This has a great advantage in image acquisition in low light environments, with better performance at high frame rates. Back-illuminated CMOS sensors are often high-speed chips, and many chips support full-HD image output at a frame rate of 60 frames per second or more. In this regard, CCD sensors are more difficult. Most mainstream HD cameras using back-illuminated CMOS sensors now support 1080P@30fps Full HD video or 720P@60fps.

And our common CCD sensor camera can only 720p @ 25fps, support for 1080P format CCD sensor costly. Back-illuminated CMOS sensor pixels can be higher. Although both back-illuminated CMOS and CCD can increase effective pixels. However, when the structure of the back-illuminated CMOS determines that the sensor area does not change, the effective pixels can be further improved and the image quality can be maintained better. In contrast, if the CCD blindly raises the pixels, the picture quality will be very poor, and as the pixels increase, the chip size will also increase and the cost will increase geometrically.

The CCD sensor manufacturing process is more complicated, and the price of cameras using CCD sensors will be relatively high. In fact, after technological transformation, the gap between the actual effects of CCD and CMOS has been reduced a lot. Moreover, the manufacturing cost and power consumption of CMOS chips are much lower than those of CCDs, so many high-definition camera manufacturers use CMOS image sensors. Imaging: In the same pixel under the CCD imaging permeability, sharpness is very good, color reproduction, exposure can guarantee the basic accuracy. The CMOS products currently have a general screen permeability, and have poor color reproduction capabilities. In most exposure modes, the Rolling Shutter mode causes high-speed moving object sensors to have a problem of distortion. The CMOS image quality and the CCD sensor are There is still a certain distance in the scene where quality requirements are more stringent. However, due to the low price and high degree of integration, it has been widely used in the rapidly developing high-definition camera market.

The latest development of image sensors

The CMOS image sensor was favored by the market in 2012. The important reason is that in the past, the sensitivity problem of the CCD was much lower than that of the CCD. Due to the use of new sensor technologies, such as back-illuminated CMOS, it was gradually solved. Compared with CCD sensors, CMOS sensors have better mass production, and it is easy to implement SoC (System on Chip) products including other logic circuits, which is difficult to achieve in CCD chips. In particular, a CMOS sensor does not require a special manufacturing process like a CCD chip, and thus can directly use a production equipment for large-volume products such as DRAM. In this way, the CMOS image sensor may form a completely different cost structure from the CCD image sensor, and it also opens up a new direction of development for the high degree of integration of the CMOS sensor. In the early market, CMOS sensors were introduced with their own ISP processor, containing 2A (AE, AWB) control algorithm. And so far, such products have been very popular and favored by the market.

Many small businesses that do not have the ability to develop ISP image processor/ISP algorithms can use their own 2A CMOS sensors to manufacture high-definition cameras. In the traditional high-definition camera architecture, the front-end to the back-end is generally divided into several components: the image sensor SENSOR, the ISP image sensor, and the compression/signal conversion processing; and if an integrated ISP CMOS sensor is used, the middle part is implemented using an FPGA chip. The ISP unit can be omitted, which not only effectively reduces the overall BOM cost of the device, but also bypasses the R&D threshold of the ISP algorithm. Most of the 720P HD network cameras that are cheaper on the market today use such solutions.

The integrated Real frame-level, wide dynamic, ultra-wide dynamic HD back-illuminated CMOS sensor is different from the previous CMOS SENSOR with integrated 2A function. This product uses the frame-level wide dynamic technology of sensor manufacturers. We know that for the image processing of high-definition cameras, especially the ISP partly relies on not only R&D strength, but also on the extensive experience in image processing debugging. Then a back-illuminated CMOS sensor with its own frame-level dynamic function not only increases the dynamic range of the sensor to more than 120dB, but also saves R&D investment for camera manufacturers.

In addition to the above-mentioned image sensor integrated with ISP image processing, it is one of the directions for the market to introduce an image sensor with integrated compression processing. The high degree of integration of the camera's core components is the future trend, thanks to the better mass production of CMOS sensors and the ease of implementation of architectural features that include other logic circuits.