Backside-illuminated, high-QE, 3e- RoN, fast 700fps, 1760x1680 pixels CMOS imager for AO with highly parallel readout
2012
The success of the next generation of instruments for 8 to 40-m class telescopes will depend upon improving the image
quality (correcting the distortion caused by atmospheric turbulence) by exploiting sophisticated Adaptive Optics (AO)
systems. One of the critical components of the AO systems for the E-ELT has been identified as the Laser/Natural Guide
Star (LGS/NGS) WaveFront Sensing (WFS) detector. The combination of large format, 1760x1680 pixels to finely
sample (84x84 sub-apertures) the wavefront and the spot elongation of laser guide stars, fast frame rate of 700 (up to
1000) frames per second, low read noise ( 90%) makes the development of such a device
extremely challenging. Design studies by industry concluded that a thinned and backside-illuminated CMOS Imager as
the most promising technology. This paper describes the multi-phased development plan that will ensure devices are
available on-time for E-ELT first-light AO systems; the different CMOS pixel architectures studied; measured results of
technology demonstrators that have validated the CMOS Imager approach; the design explaining the approach of
massive parallelism (70,000 ADCs) needed to achieve low noise at high pixel rates of ~3 Gpixel/s ; the 88 channel
LVDS data interface; the restriction that stitching (required due to the 5x6cm size) posed on the design and the solutions
found to overcome these limitations. Two generations of the CMOS Imager will be built: a pioneering quarter sized
device of 880x840 pixels capable of meeting first light needs of the E-ELT called NGSD (Natural Guide Star Detector);
followed by the full size device, the LGSD (Laser Guide Star Detector). Funding sources: OPTICON FP6 and FP7 from
European Commission and ESO.
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