4 Final Report - Emits - ESA

4 Final
Report
sub-block has16 video outputs with 20 Mpixels/s data rate, allowing reading the total array in less than
100 msec.
Column decoder
16 outputs 16 outputs
Column readout circuit
4 stitched 25 Mpix arrays
Column readout circuit
16 outputs 16 outputs
Column decoder
Figure 4.3-8: Architecture for the CMOS detector for PAN , UV-Blue & Red-NIR focal planes
Each detector is interfaced with a Proximity Electronics Module (PEM) housing all the functions
requiring to be located close to the detector, i.e. detector sequencing (e.g. clock generation), bias
voltage supply and video signal pre-amplification.
4.3.3.3 MWIR focal plane
The selected technological approach is that photo-detectors arrays are manufactured by using the
adequate detection material and hybridised on top of a CMOS Read Out Integrated Circuit (ROIC).
The ROIC is in charge of providing the reference bias voltage to each photo-detector, injecting the
signal at the output of the photo-detector within the corresponding integration capacitance and
multiplexing the analogue signals from all the pixels through a reduced number of outputs.
AlGaAs/GaAs or InGaAs QWIP technology was initially preferred to HgCdTe for its better yield,
operability and uniformity. QWIP main drawback is its lower sensitivity. However, as MWIR integration
time is low with respect to read out time, the sensitivity should not be the driver of the choice, whereas
cost, stability, cosmetics and uniformity are important Nevertheless, this choice had to be
reconsidered when an additional SWIR channel had to implemented. Indeed, QWIP technology does
not allow wide-band detectors with good detection efficiency from 1.3 to 3.7 µm, so a dedicated SWIR
focal plane would be required. The right choice is then HgCdTe technology which allows such a
combined SWIR/MWIR detector with good detection performances, but also with the yield drawbacks
pointed out above.
Driven by the minimum pixel pitch that can be achieved for European indium bump hybridized
detectors (i.e. 15 µm), the 30x30 mm 2 area of the 2k x 2k photo-detector array assumed for Geo-
Oculus is larger than the today European state of the art (20 mm diagonal for QWIP and 25 mm for
HgCdTe, but seems reachable within a few years provided the necessary pre-developments are
performed. The CMOS ROIC associated to the photo-detector array is another challenge. Stitching will
be required, 30x30 mm 2 being larger than the stepper field.
The MWIR detector architecture is similar to the UV-VNIR one (see Figure 4.3-9).
Doc. No: GOC-ASG-RP-002 Page 4-35
Issue: 2
Date: 13.05.2009 Astrium GmbH