Principle of CCD camera
A CCD chip ( Charge-coupled device ) is a modern image detector widely used in digital cameras, video cameras and web cameras. The actual principle is quite simple, step by step is indicated in the following pictures.
The basis is a plate made of pure silicon, i.e. actually an intrinsic semiconductor. On the lower side, the semiconductor is grounded, on the other side it is covered with a layer of silicon dioxide, which acts as an insulator. Surface electrodes are vaporized on this layer.
In pure silicon, no free charge carriers are theoretically present. The positive pole of the source is connected to the electrode with number 1, the negative pole is connected to the ground. So the silicon is in an electric field. If a photon hits the silicon, some valence electron can be knocked out of the bond to the silicon atom, and thus an electron-hole pair is formed. Due to the existing electric field, these two charge carriers are separated from each other and each travel to a different side of the silicon wafer. The number of charge carriers released in this way is proportional to the intensity of the incident radiation.
In the next step, the positive charge is disconnected from electrode number 1 and attached to electrode number 2. The charge that was accumulated under electrode number 1 moves under electrode 2, i.e. to the right here in the picture.
Quite analogously, the positive charge switches from electrode 2 to electrode 3.
And finally it switches from electrode 3 to electrode 1. However, the charge has already moved one whole "cell" to the right.
By repeating, the charge reaches the edge of the silicon wafer and can exit into the attached conductor. The captured current pulse corresponds to the brightness that was applied to the evaluated pixel. Since the switching of electrodes 1−3 is controlled, we have information about where the respective pixel is located at the same time as the brightness.
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External Links[edit | edit source]
- J.Březina: CCD snímače I on the Grafika ON-LINE server
- J.Březina: CCD snímače II on the Grafika ON-LINE server
- J.Březina: CCD snímače III on the Grafika ON-LINE server
- J.Březina: CCD snímače IV on the Grafika ON-LINE server
