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Proceedings Paper

Influence of nonideal chopper design on nonuniformity in uncooled pyroelectric staring array systems
Author(s): Jochen Koepernik; Helmut Budzier; Guenter Hofmann
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Paper Abstract

Choppers are inevitable parts of thermal imager or radiometer systems based upon uncooled pyroelectric focal plane arrays, since pyroelectric detectors require the incident radiation to be modulated. In comparison with other chopper techniques such as oscillator or shutter choppers rotating circular disks are considered superior in both mechanical simplicity and electronic control. However, the use of rotating disks introduces two non-ideal circumstances affecting the system's operation quality. Two-dimensional arrays require a bended chopper edge to approximate an ideal straight edge traveling over the array. Since sampling is performed line- sequentially, a local shift in time occurs between the sampling instant and the change of the optical chopper phase within each line. Furthermore, the chopper can only be placed in front of the entrance window of a detector array and, therefore, modulates the incident radiation in the blurred region of the optical path. This flattens the ideal rectangular modulation shape one would obtain if the chopper were able to run in the focal plane. Both effects attenuate the sensor output signal. The article presents a model for designing optimum chopper disks for 2- D arrays in order to achieve minimal possible signal attenuation. The optimization procedure incorporates all interdependencies between chopper layout, array size, chopper position, and readout velocity. The model also considers the unavoidable distance of the chopper plane from the focal plane and provides a chopper performance prediction method where the varying signal attenuation is discussed as contribution to the array's nonuniformity. Finally, a sample design is given, and measurements are presented.

Paper Details

Date Published: 8 September 1995
PDF: 12 pages
Proc. SPIE 2552, Infrared Technology XXI, (8 September 1995); doi: 10.1117/12.218261
Show Author Affiliations
Jochen Koepernik, Technische Univ. Dresden (Germany)
Helmut Budzier, Technische Univ. Dresden (Germany)
Guenter Hofmann, DIAS Angewandte Sensorik GmbH (Germany)


Published in SPIE Proceedings Vol. 2552:
Infrared Technology XXI
Bjorn F. Andresen; Marija Strojnik, Editor(s)

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