1. Imaging process CCD and CMOSThe principle of photoelectric conversion of image sensors is the same. The main difference is that the signal reading process is different; since only one (or a few) output nodes of CCD read it uniformly, the consistency of its signal output is very good; while in the CMOS chip, each pixel has its own signal amplifier, which each performs charge-voltage conversion, and its signal output consistency is poor.However, in order to read the entire image signal, CCD requires that the signal bandwidth of the output amplifier is wider. In CMOS chips, the bandwidth requirements of the amplifier in each cell are lower, which greatly reduces the power consumption of the chip. This is the main reason why the power consumption of the CMOS chip is lower than that of CCD.Despite the reduced power consumption, the inconsistency of millions of amplifiers brings higher fixed noise, which is an inherent disadvantage of CMOS over CCD.
2. Integration From the perspective of manufacturing process, CCD circuits and devices are integrated into semiconductor single crystal materials manufacturers, with relatively complex processes. Only a few manufacturers in the world can produce CCD crystals, such as DALSA, SONY, Panasonic, etc.CCD can only output analog electrical signals, and requires subsequent address decoder, analog converter, and image signal processor processing. It also requires three sets of power supply synchronous clock control circuits with different voltages, with very low integration.CMOS is integrated on a monomer material called metal oxide. This process is the same as the process of producing semiconductor integrated circuits such as tens of thousands of computer chips and storage devices. Therefore, the cost of the sound field CMOS is much lower than that of CCD.At the same time, the CMOS chip can integrate image signal amplifiers, signal reading circuits, A/D conversion circuits, image signal processors and controllers into a chip. All the basic functions of the camera can be realized with only one chip. The integration level is very high, and the concept of chip-level cameras is born from this.With the continuous development of CMOS imaging technology, more and more companies can provide high-quality CMOS imaging chips, including: Micron, CMOSIS, Cypress, etc.
3. Speed CCD uses photosensitive output one by one, and can only output according to the prescribed program, and the speed is slower.CMOS has multiple charge-voltage converters and row-sequence switch controls, and the readout speed is much faster. Currently, most high-speed cameras above 500fps are CMOS cameras.In addition, the address gate switch of CMOS can be randomly sampled to realize sub-window output, and can obtain higher speeds when only sub-window images are output.
4. Noise CCD technology has developed early and is relatively mature. It uses PN junction or silica (SiO2) isolation layer to isolate noise. The imaging quality has certain advantages over CMOS photoelectric sensors.Due to the high integration of CMOS image sensors, the distance between each component and circuit is very close, and the interference is relatively serious, and the noise has a great impact on image quality.In recent years, with the continuous development of CMOS circuit noise cancellation technology, good conditions have been provided for the production of high-density and high-quality CMOS image sensors.
