1. Reading from a charge coupled device (ccd)
© D Hoult 2010

2. Each pixel in a ccd consists of a photoelectric cell and a capacitor (to store the charge emitted)

3. Each pixel in a ccd consists of a photoelectric cell and a capacitor (to store the charge emitted)
The voltage across the capacitor is proportional to the charge stored

4. Each pixel in a ccd consists of a photoelectric cell and a capacitor (to store the charge emitted)
The voltage across the capacitor is proportional to the charge stored and hence to the intensity of the illumination of the pixel

5. The pixels in this diagram have been magnified...

6. The pixels in this diagram have been magnified...
quite a lot !

7. This ccd has not yet been exposed to light

8. After exposure, the capacitors in the illuminated pixels now store a small charge

9. The data are read 1 pixel at a time

10. First, all the voltages are “shifted” towards a special row of pixels at one end of the chip

11. First, all the voltages are “shifted” towards a special row of pixels at one end of the chip

12. First, all the voltages are “shifted” towards a special row of pixels at one end of the chip

13. Now the data voltages are “shifted”, one at a time, towards a pixel at the end of that special row

14. After each shift, the voltage in the special pixel is read and stored in memory

15. After each shift, the voltage in the special pixel is read and stored in memory, in this case, zero

16. voltage = V

17. voltage = 0

18. voltage = 0

19. voltage = V

20. voltage = 0

21. voltage = V

22. voltage = 0

23. voltage = 0

24. voltage = V

25. voltage = V

26. voltage = V

27. voltage = V

28. voltage = V

29. voltage = 0