4k*4k versus 2k*4k

[Paul.Jorden at eev.com]

Posted to CCD-world:
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Hi everyone,

I've been thinking about the pros and cons of 2k*4k chips versus 4k*4k ones, 
specifically for survey mosaics.  It seems to me that in terms of focal 
plane coverage there is not much to choose between 2N 2k*4k or N 4k*4k 
chips.  Indeed, a more compact package can give the 4k*2k chip the 
advantage.  The extra gap between 2k*4k chips will not really matter for 
survey work, and will be compensated by possibly better total coverage 
anyway.

Obviously the array assembly involves twice as many chips, and is a little 
more complex, but on the other hand there is twice as much redundancy if a 
chip needs replacing.

The wiring will be somewhat more extensive for 2N chips.  However, parallel 
clocking of the 4k*4k chip may be slower, so the smaller chips could be 
preferable.  I assume that the 4k*4k chip would have 4 outputs, and the 
2k*4k chip would be 3-side-buttable with 2 outputs; so the number of data 
acquisition channels would be the same.

I assume that 2k*4k chips will always be easier to make than 4k*4k chips, 
and so there would seem to be good reasons for choosing the smaller device, 
and not many for going to the larger one.  (ie current yield statistics 
imply that a good 4k*4k chip is more than twice as hard to make as a good 
2k*4k one).

I'm thinking of large thinned CCDs really, but a similar discussion could 
apply to IR arrays I suppose.

I'd be interested to hear any comments on this discussion.

Best Regards,
Paul
_______________________________________________________________
Dr Paul Jorden,  CCD Sensors, EEV
Waterhouse Lane, Chelmsford, Essex, CM1 2QU, UK
Tel:      44 (0) 1245 -453458 (direct), -493493 (switchboard)
Fax:      44 (0) 1245 453224
see also:-     http://www.ccd.eev.com/

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