The application of charge-coupled devices to thermal imaging systems
The application of charge-coupled devices to thermal imaging systems
This thesis is concerned with the use of Charge-Coupled Devices (CCDs) to interrogate infrared photodetectors. In particular, some of the electrical interface problems associated with a hybrid infrared charge-coupled imager are investigated. A lead telluride 3-5um infrared photodetector coupled to a silicon CCD is considered. The CCD input characteristics are analysed for a source coupled direct injection technique in which the MOS input structure is operating largely subthreshold. The performance of the combination is evaluated in terms of the injection efficiency, bandwidth and noise equivalent temperature difference (NETD). The high capacitance of the lead based detector produces a low bandwidth when operated in this mode and as a result, such detectors are unsuited to most currently anticipated fast imaging systems. The high background level and low contrast of normal terrestrial infrared signals can pose severe problems for the signal handling capacity of a CCD. These difficulties can be eased by discarding the background signal before injection into the CCD. The contrast part of the signal can then be made to occupy a larger portion of the CCD's dynamic range. A novel method for doing this has been devised. The scheme uses a charge pump circuit to remove the constant background signal. A prototype system has produced a factor of 2.6 improvement in NETD for a room temperature thermal scene, in agreement with the theoretical result. Further improvements are postulated for when a modified circuit arrangement is used, and also for devices operating in the 8-14um infrared window where the contrast is smaller.
University of Southampton
Frier, Alistair Arthur Grant
1982
Frier, Alistair Arthur Grant
Frier, Alistair Arthur Grant
(1982)
The application of charge-coupled devices to thermal imaging systems.
University of Southampton, Doctoral Thesis.
Record type:
Thesis
(Doctoral)
Abstract
This thesis is concerned with the use of Charge-Coupled Devices (CCDs) to interrogate infrared photodetectors. In particular, some of the electrical interface problems associated with a hybrid infrared charge-coupled imager are investigated. A lead telluride 3-5um infrared photodetector coupled to a silicon CCD is considered. The CCD input characteristics are analysed for a source coupled direct injection technique in which the MOS input structure is operating largely subthreshold. The performance of the combination is evaluated in terms of the injection efficiency, bandwidth and noise equivalent temperature difference (NETD). The high capacitance of the lead based detector produces a low bandwidth when operated in this mode and as a result, such detectors are unsuited to most currently anticipated fast imaging systems. The high background level and low contrast of normal terrestrial infrared signals can pose severe problems for the signal handling capacity of a CCD. These difficulties can be eased by discarding the background signal before injection into the CCD. The contrast part of the signal can then be made to occupy a larger portion of the CCD's dynamic range. A novel method for doing this has been devised. The scheme uses a charge pump circuit to remove the constant background signal. A prototype system has produced a factor of 2.6 improvement in NETD for a room temperature thermal scene, in agreement with the theoretical result. Further improvements are postulated for when a modified circuit arrangement is used, and also for devices operating in the 8-14um infrared window where the contrast is smaller.
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Published date: 1982
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Local EPrints ID: 459903
URI: http://eprints.soton.ac.uk/id/eprint/459903
PURE UUID: 6d2a7008-6123-4e15-8fc4-943c624497e5
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Date deposited: 04 Jul 2022 17:24
Last modified: 04 Jul 2022 17:24
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Author:
Alistair Arthur Grant Frier
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