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

[Bruce Truax]

The following was posted to CCD-world:

Roy,

I was involved in a project using these cameras for another application, 
and while they are good in many ways, we had a similar problem.  We never 
quite tracked down the source.  In our application which was more of a 
gray scale imaging problem, we noticed distortion at the beginning of 
lines which appeared to depend on the intensity at the end of the 
previous line.  We were using the camera for a heterodyne detection 
scheme so we were not sensitive to gain or bias differences but non 
linearity and signal mixing between channels were a problem. I think that 
the problem was greater than 1 bit in amplitude, but only because of the 
type of detection we were using.  If we were taking astronomical images, 
we probably would not have seen the problem without multiple images.

The project is still using these cameras, but we have realized that to 
improve the performance further, we will have to switch away from SMD.

Bruce Truax

>On 3/22/2000 11:37 AM, tucker at noao.edu said:

>	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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