CCD-world: cross-talk in multi-channel CCDs
Skipper, Mark
skipper at siraeo.co.uk
Mon Apr 10 12:27:49 CLT 2000
The following was posted to CCD-world:
Roy and All
In addition to Tom's suggestions you can generate a good CCD video
signal by using the Readout register clock that trasfers the charge to the
output, R2 on a two phase CCD. Link the clock to the output via a resistor
divider and a AC coupling cap. A resistor from Vod to Vos will get the DC
voltage correct.
At the levels you are talking about the cross-talk could be optical
due to stray light in the optical setup, so the elimination of the CCD is a
good starting point.
Regards Mark
> -----Original Message-----
> From: Hopkinson, Gordon
> Sent: 03 April 2000 18:26
> To: Skipper, Mark
> Subject: FW: CCD-world: cross-talk in multi-channel CCDs
>
>
>
> ----------
> From: Tom Droege[SMTP:droege at wwa.com]
> Reply To: CCD-world at astro.ku.dk
> Sent: 23 March 2000 15:01
> To: CCD-world at astro.ku.dk
> Subject: Re: CCD-world: cross-talk in multi-channel CCDs
>
> The following was posted to CCD-world:
>
> Roy and all,
>
> First I will second Barry's recommendation. The Analog Devices technical
> notes on grounds are just great!
>
> Here is a suggestion on how to test. Remove the CCD. Apply a pulse
> generator to one of the outputs and run the system. You will probably
> have
> to kludge up something to generate the signal you need. But this is a
> tough problem and will require some preperattion. Now get a fast
> differential scope probe. Tektronix makes some nice ones. Now you can go
> around taking differences between grounds. With say a 1 volt pulse (or
> whatever the front end amplifiers will stand withoug saturation) and 100
> uv
> or so sensitivity on the differential probe, you should be able to see a
> lot of stuff on the grounds. This just may lead you to a solution.
> Cross talk is a tough business at this level. Don't expect an easy
> solution. Don't hesitate to build up something to test properly. It is
> easy to spend a lot of time on little quick fixes that do not work when a
> more elaborate carefully executed plan will solve the problem.
>
> Errrr! Possibly you are using a multi-layer board with a common ground
> plane under the four channels. I would not do this. Four separate ground
> planes, connected at one point is the way I would go. Of course separate
> analog and digital ground planes with the digital plane separate from the
> analog plane. You can use one layer for both but separate them between
> analog and digital.
>
> I repeat my suggestion of making a good diagram. Every place there is a
> common tie between two grounds draw in an inductor. Put capacitors
> between
> everything on the diagram. Remember that the ground plane (if you have
> one, I would not) couples capacitively between everything.
>
> Sigh! A tough problem. Good luck with it and please keep us informed.
> It
> is often more important to learn how not to do things than how to do
> things.
>
> Tom Droege
>
> At 11:27 AM 3/22/00 -1000, you wrote:
> >The following was posted to CCD-world:
> >
> >Hi Roy,
> >
> >Photon-forager, I like that, maybe Photon-phorager or Foton-forager...
> >
> >Anyway back to the matter at hand...
> >
> >The first thing I'd ask is have you tested your acquisition system
> >performance separately from the CCD. If you still have the problem it's
> >not the device (or only the device at least at the level your currently
> >experiencing) if it goes away then either it's the CCD or your interface
> >to the CCD. Split the chain if you can to see what's your offending
> >party....
> >
> >Regarding decoupling of video amplifiers, often the addition of more
> >capacitance does not improve your decoupling due to the resonant
> >frequency issues of non-ideal capacitors. Often you need to parallel
> >0.01uf ceramics with 1uF tantalums (surface mount best, extremely short
> >leads mandatory) to get solid wideband decoupling. There is a wonderful
> >application note by Analog Devices AN-202 "An IC Amplifier User's Guide
> >to Decoupling, Grounding and Making Things Go Right for a Change" by
> >Brokaw that's a classic (great title as well). But there's a load of
> >good info for Analog Devices, Burr-Brown, and Linear Technology
> >application notes in this area.
> >
> >
> >Good Luck,
> >
> >Barry
> >
> >Roy Tucker wrote:
> >>
> >> 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
> >>
> >> - -- CCD-world -- --
> >> CCD-world is fully moderated. Send posts to CCD-world at astro.ku.dk
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> manually.
> >> For more information, please go to: http://www.not.iac.es/CCD-world/
> >
> >--
> >_________________________________________________________________________
> ____
> >
> >Barry Michael Starr
> >starr at cfht.hawaii.edu
> >Canada France Hawaii Telescope Ph: 808-885-3139
> >PO BOX 1793 Kamuela, HI 96743 Fax:
> >808-885-7288
> >_________________________________________________________________________
> ____
> >- -- CCD-world -- --
> >CCD-world is fully moderated. Send posts to CCD-world at astro.ku.dk
> >Standard replies will go to the list; address personal replies manually.
> >For more information, please go to: http://www.not.iac.es/CCD-world/
> >
> - -- CCD-world -- --
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>
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