By incorporating on-chip multiplication gain, the electron multiplying CCD achieves, in an all solid-state sensor, the single-photon detection sensitivity typical of intensified or electron-bombarded CCDs at much lower cost and without compromising the quantum efficiency and resolution characteristics of the conventional CCD structure.
Under conditions where a CCD is exposed to very high intensity illumination, it is possible to exhaust the storage capacity of the CCD wells, a condition known as blooming. When this occurs, excess charge will overflow into adjacent CCD photodiode wells resulting in a corrupted image near the blooming site. This tutorial explores the operation of a lateral overflow drain to prevent CCD blooming.
A common CCD anti-blooming technique involves "overflow" drain structures that are incorporated into the CCD during fabrication. Two of the most common drain structures are the vertical overflow drain (VOD) and the lateral overflow drain (LOD), illustrated above. Drains enable integration time to be controlled independently of charge readout, which allows them to serve as an electronic exposure or shutter mechanism to limit pixel saturation and provide a more reliable shuttering method than is currently possible with mechanical devices.
When the tutorial initializes, two sliders appear that control photon wavelength (color) and illumination intensity. Use the Photon Intensity slider to adjust the number of photons striking the CCD during a unit time period. The Illumination Wavelength slider can be used to control the wavelength of incoming photons.
Mortimer Abramowitz - Olympus America, Inc., Two Corporate Center Drive., Melville, New York, 11747.
Tadja Dragoo and Michael W. Davidson - National High Magnetic Field Laboratory, 1800 East Paul Dirac Dr., The Florida State University, Tallahassee, Florida, 32310.