Dark current is very detrimental to the quality of CCD imaging
ANSWER: The dark current (Dark, Current) is due to electron hole pairs produced by thermal excitation In the real world, all image sensors are affected by dark currents, because we can’t create an environment where the temperature is Kelvin’s absolute zero For semiconductor devices, as long as their temperature is not Kelvin absolute, the electron hole pairs within the component are always in dynamic equilibrium of generation, migration and annihilation The higher the temperature, the faster the electron hole generation and migration, i e , the greater the dark current It should be pointed out that the variation of temperature and the magnitude of dark current are nonlinear For example, the temperature decreases by 6 degrees each time, and the dark current is reduced by about half Dark current measurement units are electronic primitive sec Under normal temperature, numerical dark current is about 250-1000 per second, a primitive 1000 electron charge is not big, but you know, for a 512X512 CCD, the number of primitives is about 262000 per second, to read the map is about 6553600, so that the "undercurrent " is not an exaggeration In the process of manufacturing CCD, the technology commonly adopted is "photolithography mask + ion penetration " This process cannot guarantee that every lattice in CCD has exactly the same stability in each element; in other words, each element has the same ability to produce electron hole pairs under the same conditions The defect of the CCD itself is an important reason for the generation of dark current, and the defect of the device also makes the generation of dark current uneven, and also produces fixed graphics at CCD in non illumination environment Dark current is very detrimental to the imaging quality of CCD, and it also limits the sensitivity and dynamic range of the device
The heat sink prevents CCD from aging
ANSWER: Interestingly, the signal-to-noise ratio of CCD is not only related to temperature, but also related to the degree of aging of CCD devices By comparison, we can see that the new CCD device has a high signal-to-noise ratio High temperature is a common factor in accelerating the aging of electronic devices This is another long-term impact of temperature on the quality of CCD imaging In order to reduce the influence of ambient temperature on CCD signal-to-noise ratio, it is an effective measure to provide heat sink for CCD In Figure 2, the line A indicates that the CCD has a heat sink, and the line B represents the heat dissipation of the wafer itself As can be seen, the same CCD, the noise ratio of the heat sink is about two times that of the heat sink
The signal to noise ratio decreases sharply with the increase of temperature
ANSWER: Generally speaking, the main noise source of CCD has the following three kinds: first, the photon injection device converts light charge generated by noise; second light, charge transfer, charge generation quantity fluctuation noise; third, when the light charge readout noise The law of thermodynamics indicates that the higher the temperature, the higher the average kinetic energy of electrons, the higher the uncertainty in the conversion, transfer and output of light charges, which means that the noise of CCD is stronger In addition, Einstein’s theory of photoelectricity expounds that the occurrence of photoelectrons is related to incident photons, and the temperature independent, that is to say, the signal intensity of CCD does not increase with the increase of temperature Therefore, the signal-to-noise ratio of CCD decreases sharply with the increase of temperature
Influence of QUESTION: temperature on CCD imaging
ANSWER: signal-to-noise ratio (SNR) in value refers to the ratio of voltage signal noise voltage, its physical meaning is the relative size of signal and uncertain signal is obtained based on each primitive; in applications that require accurate image, high signal-to-noise ratio is particularly important
There are several categories of QUESTION: surveillance cameras
ANSWER: ANSWER: camera consists of analog cameras and digital cameras, the simulation of bolt, hemisphere, waterproof infrared machine, ball machine etc Digital cameras, in general, are webcams