Image sensors and optical devices

What does the "fill factor" of an image sensor pixel mean?

  1. AThe size of the lens aperture
  2. BThe ratio of effective pixels to total pixels
  3. CThe fraction of the pixel area that receives light and converts it to charge
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Answer: C. The fraction of the pixel area that receives light and converts it to charge

Fill factor is the fraction of a pixel's area that can receive light as a photodiode. When transistors and wiring block much of the light, the fill factor drops and sensitivity falls. Microlenses and back-side illuminated structures are ways to raise the effective fill factor.

  • A. The lens aperture is expressed by the f-number and differs from pixel fill factor.
  • B. The ratio of effective pixels is a separate metric.
  • C. Correct. It is the fraction of the pixel area that can receive light.
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