CCD-world: cross-talk in multi-channel CCDs

[Roy Tucker]

The following was posted to CCD-world:

Dear Fellow Photon-Foragers,

	I am participating in the up-grading of the GONG
(http://www.gong.noao.edu) video data system which includes a new camera
(Silicon Mountain Designs 1M60-20) with a Thomson THX7887A imager
(frontside 1024 square array, four channels of 1024 x 256, 14 um pixels, 60
frames per second, 12 bits per pixel). Our data acquisition algorithm
consists generally of co-adding images for 60 seconds into three or six
accumulation buffers in synchrony with the angular orientation of rotating
optical elements in the system. Co-adding 600 or 1200 12-bit numbers
produces approximately 23-bit results.

	We are noticing a low-level (far below the 12-bit resolution of an
individual image) cross-talk between the four output channels of the
camera. The phenomenon is non-linear in that it does not appear until a
threshold luminance level is reached. Our initial hypothesis that there
were insufficient bypass capacitors associated with the video amp power
supply rails and CCD bias voltages appears to have been disproven by an
experiment involving the installation of larger caps. There appeared to be
no beneficial effect.

	Although not a serious problem, we would like to reduce or eliminate the
effect if possible. Before proceeding further with our testing, we thought
it might be wise to consult the CCD engineering community to see if anyone
else has seen such an effect and if they could indicate to us if it is due
to the CCD support electronics or an inherent property of this particular
CCD imager or multi-channel CCDs in general.

	Thank you very much for your attention.

					Best regards,
					  Roy Tucker


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