Image sensors and optical devices

What is the purpose of correlated double sampling (CDS) used in CMOS image sensor readout?

  1. ATo amplify the signal twofold
  2. BTo interpolate color information
  3. CTo take the difference between the reset level and the signal level, removing reset noise and per-pixel offsets
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Answer: C. To take the difference between the reset level and the signal level, removing reset noise and per-pixel offsets

CDS samples the output right after the pixel is reset and the output when the light signal is read, and uses the difference as the signal. Noise that varies with each reset and the offsets of each pixel's amplifier cancel out, giving images with less noise.

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