This paper was presented at the Workshop
IMAGING FOUIER TRANSFORM SPECTROMETERS-IFTS
AND THE PROPOSAL
SOLAR PHYSICS ELEMENT IN COLUMBUS/SPACE STATION-SPECS
held at The Institute of Theoretical Astrophysics, University of Oslo, May 30, 1990.
The workshop was organized by P.Maltby. The paper is printed on pages
51 to 54 of the Proceedings of this workshop. The report was compiled/edited
by P.Maltby.
SIGNAL PROCESSING IN INSTRUMENTS BASED ON INTERFEROMETRY
T. Jæger and J.K. Hagene
Norsk Elektro Optikk A/S, P O Box 17
N-2001 Lillestrøm, Norway
(May 1990) (See below for updated address.)
Norsk Elektro Optikk A/S has been involved in two feasibility studies for
ESA concerning imaging spectroscopy using Fourier Transform Spectrometers.
In this class of instruments the signal processing hardware is of importance
since the spectral information should be extracted from the interferograms
by on board calculations. A properly designed signal processing system
will reduce the amount of data that have to be transmitted to ground.
Norsk Elektro Optikk A/S has proposed a new concept for signal processing
circuitry very well suited for doing Fourier Transforms in applications
where only a part of the possible spectral components is of interest.
The selected spectral components are freely programmable among all possible
spectral components.
The Discrete or Direct Fourier Transform (DFT) is the selected signal
processing method. The DFT is advantageous compared to the often used
Fast Fourier Transform (FFT) because it do not need buffering of input data
and because the number of samples in the interferogram can be different
from 2^n. The DFT also allows you to compute only a selected number of
spectral components. The FFT, on the contrary, requires computation of
all spectral components. Using the FFT all input samples must have arrived
before a calculation can start. The DFT can be calculated "on the fly" and
therefore lends itself to pipeline realization.
No data buffering and possibilities for pipeline realization are features
of great importance for hardware implementation. Norsk Elektro Optikk A/S
has proposed to use Application Specific Integrated Circuits (ASICs) in
the signal processing system. A set of identical ASICs is operating
in parallel and doing the Discrete Fourier Transform.
The use of Application Specific Integrated Circuits gives a solution with
the lowest power and volume requirements. An ASIC solution also have the
lowest chip count. Norsk Elektro Optikk A/S has proposed to use the
residue number system internally in the ASICs. The residue number system
gives small, but fast arithmetic blocks operating in parallel.
Silicon Compiler technology could dramatically reduce the total design
time and the total time necessary for space qualification of the ASIC
component. A Silicon Compiler is a program that generates the layout of
an ASIC from a high level description of the wanted function. The layout
generated by the Silicon Compiler is from a functional point of view "correct
by construction". When it comes to space qualification the use of a
Silicon Compiler could be favourable. The process/technology itself could
be space qualified and the layout could be in accordance with design
guidelines for space applications.
The signal processing concept is described in further detail in the
following publications:
- "Very High Performance Signal Processing
using the Residue Number System",
by Oddvar Søråsen, Yngvar Lundh and Jon Kristian Hagene.
Paper accepted for presentation at the Sixth MIT
conference on Advanced Research in VLSI held at Massachusetts
Institute of Technology, April 1990.
- Feasibility study of a High Resolution Imaging Interferometer
(HRII),
Estec Contract Number 7943/88/NL/JS.
Prepared by Norsk Elektro Optikk A/S.
- Feasibility study of a high spectral resolution sounder
(HSRS).
Estec Contract Number 8575/89/NL/JS
Prepared by Aerospatiale, Officine Galileo and Norsk Elektro Optikk A/S.
Norsk Elektro Optikk responsible for signal processing.
Norsk Elektro Optikk A/S has proposed to ESA that a breadboarding of the
basic ASIC building block in the HSRS-instrument should be done. This
bredboarding could be useful also for other interferometry projects.
Figures and tables are not included on this page.
The current address of Norsk Elektro Optikk A/S is
P.O. Box 384
N-1471 Lørenskog, Norway.
Web: www.neo.no
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