The CCD sensor was invented in 1969 by Willard Boyle and George E. Smith of AT&T Bell Labs. Originally intended as a memory device
Pixel: Picture Element CCD: Charge-Coupled Device CMOS: Complimentary Metal-Oxide Semiconductor Panchromatic: Sensitivity to a wide range of wavelengths of light.
1. Photoelectric effect creates an electron-hole pair when light impinges upon a semiconductor 2. Each pixel accumulates a charge 3. When sampled, the “bucket of charge” for each pixel is transported off-chip to on off-chip amplifier 4. A capacitor is used to convert the charge to a voltage. V = q/C
Used largely in military and scientific applications. The image-intensifier is added to a CCD to create an intensified CCD. Provides single-photon sensitivity Also enables extremely short exposure times. (down to 200ps) It reduces the shortcomings of a bare CCD
PhotocathodeMicro-channel Plate (MCP)Phosphor Screen CBA A: 200V Gating Voltage (variable) B: 1000V Micro-channel plate C: 6kV acceleration voltage A > 0: Shutter is open (gated) A < 0: Shutter is closed
A: 200V Gating Voltage (variable) B: 1000V Micro-channel plate C: 6kV acceleration voltage A > 0: Shutter is open (gated) A < 0: Shutter is closed PhotocathodeMicro-channel Plate (MCP)Phosphor Screen CBA e-e- e - s (1000x)
PhotocathodeMicro-channel Plate (MCP)Phosphor Screen
Is officially defined as the percentage of photons hitting a surface that will produce electron-hole pairs › Regular photographic film is about 10% › Human Eye is about 3% › CCDs can have a QE of more than 90% at some wavelengths Useful for rating solar cells Doesn’t account for unwanted recombination in material
Quantum Efficiency of CCD used in Hubble Space Telescope’s Wide-Field and Planetary Camera 2
When charges are shifted from pixel to pixel it is the loss associated with each shift. A value of is actually bad! Most CCDs use shifts to read a single pixel out.
Thermal excitations can excite electrons into the conduction band This is the reason that most CCDs require extensive cooling (-90 to -40 °C)
Electronic amplifiers are not perfect and introduce their own noise. This determines the “noise floor” of the CCD. It sets the limitation of how faint of an object a CCD can see.
Optically insensitive structures for each pixel (absorption loss) Natural reflection of certain wavelengths (reflection loss) Very long and very short wavelengths pass straight through sensor without generating an electron (transmission loss)
CCDs are simple application of the photoelectric effect Intensified CCDs improve the light sensitivity of a bare CCD Intensified CCDs are used in military and scientific application (mostly astronomy)
al_Camera.pdf al_Camera.pdf per_Digital_Cinema_ _03-70.pdf per_Digital_Cinema_ _03-70.pdf