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Amplifier Promises To Improve Charge-Coupled Devices

Photonics Spectra
May 1997
Kathleen G. Tatterson

LOS ALAMOS, N.M. -- A charge-coupled device (CCD), the component that converts light into electronic signals in scientific and commercial imaging instruments, is only as good as its amplifier. A new amplifier developed at Los Alamos National Laboratory could allow such devices to run 10 times faster than previously possible in scientific applications -- with the same dynamic range.
CCDs operating in the average commercial video camera perform at speeds of 60 fps and high noise levels because of the 6- to 10-MHz video bandwidth. Conversely, devices employed in scientific applications, such as the Hubble Space Telescope, operate with lower noise levels, a dynamic range up to 18 bits, up to 1 fps.
The new amplifier will allow CCDs to operate in scientific video applications at 10 fps and slow speeds with the same performance as 1-fps cameras, according to Mark Dunham of the Los Alamos team.
The secret lies in the amplifier's proprietary circuit configuration. The amplifier topology uses a large geometry common source field-effect transistor, producing a current mode output for further off-chip amplification. The off-chip amp lifiers are designed to work with the on-chip transistor to produce a complete output amplifier with a low- noise video signal.
The US Department of Energy's Alexis satellite project sponsored the work that has led to the device's development. The new technology could lead to CCD applications in engineering and process control, Dunham said. Although no company has commercialized the amplifier to date, many have expressed interest, particularly in the field of scientific imaging.
However, manufacturers will need to consider its overall cost versus sensitivity.
"The integrated circuit re-engineering costs associated with this invention mean that only applications needing high sensitivity at video-frame rates will drive the commercialization of this technology," said Dunham. "This is especially true since scientific CCDs can now detect one photon at 0.01 fps rates.

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