CCD Primer

Bracket Pulsing
CCD Grading
Cosmic Rays
Dark Current
Deep Depletion CCD
Detection Modes
Dual Capacity Mode
Dual Readout Mode
Dynamic Range
Etaloning in CCDs
UV Extension
Fiber Optics
Flat Fielding
Full Well Capacity
Image Calibration
Imager Architectures
Image Intensifiers
Kinetics Mode
Matching Resolution
MPP Mode
Noise Sources
On-chip Multiplication Gain
Open Poly CCD
Optical Window
Quantum Efficiency
Readout vs Frame Rate
Reducing Dark Current
Saturation/ Blooming
Signal to Noise Ratio
Spurious Charge
XP Cooling

Noise Sources

All electronic circuitry generates undesirable noise. The effect of this noise on performance is described by the signal-to-noise ratio (SNR). Photon noise, preamplifier noise and dark current noise are the three primary sources of noise in a CCD camera.

Photon Noise
Photon noise, also known as photonic or photon shot noise, is a fundamental property of the quantum nature of light. The total number of photons emitted by a steady source over any time interval varies according to a Poisson distribution. The charge collected by a CCD exhibits the same Poisson distribution, so that the noise is equal to the square root of the signal. Photon noise is unavoidable and is always present in imaging systems; it is simply the uncertainty in the data.

Preamplifier Noise
Preamplifier noise, also called read noise, is generated by the on-chip output amplifier. This noise can be reduced to a few electrons with the careful choice of operating conditions.

Dark Current
Dark current, or thermally generated charge, can be measured and subtracted from data, but its noise component cannot be isolated. Dark current noise is of particular concern in low light applications. 

Spurious Charge
Spurious charge is generated on the leading edge of the drive clock which is when the phase assumes the non-inverted state and holes are forced back to the channel stop regions. The falling edge of the drive clock has no influence on spurious charge generation in CCDs. Spurious charge increases exponentially with clock rise time and voltage swing, sending holes back to the channel stop. A fast moving, high amplitude clock increases impact ionization.