The difference between CMOS and CCD:

1. Manufacturing the imaging process

The principle of photoelectric conversion of CCD and CMOS image sensor is the same, the main difference between them is that the signal reading process is different; Because CCD has only one (or a few) output nodes to read uniformly, its signal output consistency is very good; In CMOS chip, each pixel has its own signal amplifier, which carries out charge-voltage conversion respectively, and the consistency of its signal output is poor. However, CCD in order to read out the entire image signal, the signal bandwidth of the output amplifier is required to be wide, and in the CMOS chip, the bandwidth requirements of the amplifier in each pixel are low, which greatly reduces the power consumption of the chip, which is the main reason why the power consumption of the CMOS chip is lower than that of the CCD. Despite the reduced power consumption, the inconsistency of millions of amplifiers leads to higher fixed noise, which is the inherent disadvantage of CMOS over CCD.

2. Integration

From the point of view of the manufacturing process, the circuit and device in CCD are integrated on the semiconductor single crystal material, the process is more complex, and only a few manufacturers in the shi world can produce CCD wafers, such as DALSA, SONY, Panasnic and so on. CCD can only output analog electrical signals, requires subsequent address decoder, analog converter, image signal processor processing, and also needs to provide three groups of different voltage power synchronous clock control circuit, the integration is very low. CMOS is integrated in a semiconductor material called metal oxide, which is the same process that produces tens of thousands of semiconductor integrated circuits such as computer chips and memory devices, so the cost of producing CMOS is much lower than that of CCD. At the same time, the CMOS chip can integrate the image signal amplifier, signal reading circuit, A/D conversion circuit, image signal processor and controller into a chip, only one chip can realize all the basic functions of the camera, the integration is very high, the concept of chip-level camera is generated 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 and so on.

3. Speed

CCD adopts photosensitive output one by one, which can only be output according to the specified procedure, and the speed is slow. CMOS has multiple charge-voltage converters and row and column switch control, and the readout speed is much faster, and most high-speed cameras above 500fps are CMOS cameras. In addition, the CMOS address strobe switch can be randomly sampled to realize sub-window output, and higher speed can be obtained when only sub-window images are output.

4. Noise

CCD technology developed earlier, more mature, using PN junction or silicon dioxide (SiO2) isolation layer to isolate noise, imaging quality relative to CMOS photoelectric sensor has a certain advantage. Due to the high integration degree of CMOS image sensor, the distance between the components and circuits is very close, the interference is relatively serious, and the noise has a great impact on the image quality. With the continuous development of CMOS circuit noise reduction technology, it provides a good condition for the production of high density and high quality CMOS image sensors.

FAQ: