Electronic image carriers – CCD and CMOS

First and foremost, CCD and CMOS sensors work internally according to the same scheme described above. The difference lies in the method of reading out the voltage values. The CCD sensor operates by transferring charges from one sensor cell to another, following the bucket brigade principle, until the end of each line. The readout register pushes them out in predetermined cycles. This process generates an analog serial signal by reading out the CCD chip line by line. The CMOS chip converts the charge of each sensor cell into a voltage value and transfers it to a vertical column bus, which can address each cell individually. This method transmits all data in parallel with the location information, significantly accelerating the process. Moreover, the elimination of the need to transport electrical charges across adjacent sensor elements prevents image errors, including blooming.

For a long time, CMOS chips were less common than CCD chips due to their higher noise and lower dynamic range at the beginning of development. However, due to their fundamental design, they offer significant advantages. Firstly, they are cheaper to produce because CMOS technology is standard chip production technology, and secondly, CMOS chips offer the possibility of integrating further components for signal processing. This means that analog-to-digital conversion and signal amplification can be performed „on chip“, enabling faster readout of information and more compact designs. And the CMOS chip also beats the CCDs in terms of energy consumption, consuming 2/3 less than them.

What both sensor types have in common, however, is their spectral sensitivity, which differs from that of the human eye. At around 1,000 nm, it extends much further into the long-wave red spectrum, and at 400 nm on the short-wave side, it only reaches our vision’s limit. But don’t worry; infrared filters prevent the passage of wavelengths above 750 nm, bringing digital technology closer to us than classic silver film.

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