CCD-world: EEv 4220 sensors.

[C.GUILLAUME]

The following was posted to CCD-world:

Dear all;

Planning to build new astro cameras a couple of years ago,
we have got 4220 CCd models (2 grade 0 for final camera and
one electrical grade for evaluation tests).
The difference between the astro chips and the electrical one is:
Astro models are coated while electrical is not.
All the tests were made with the electrical chip in standard EEV
preconized polarisation voltages; i.e  Vss =+9v a.s.o...
We could verify the output gain which was 4.3uv/e-.
but, we met a noise problem due to our ground system;
difficult to solve. So we decided to change polarisation voltages
and to put Vss=0v. At OHP, we used to polarize our CCd that way,
 and we never found problems .

 After consulting EEV engineers who told us
that ift was not forbidden provide the other voltages and clocks level
should be drawn downward of about 9v. And the output resistor load
should be set so that the output current stays in a good value.
EEV alos said that noise could be increased using that scheme polar;
because the ADC noise induced in the ground circuit.
So we modified all voltages as invited by EEV.

In fact it was not exactely what we observed. The noise has dramatically
 fallen , rather nice ! But we forgott to verify the output gain....
Then , since we had observed a very good noise ( remember it was an
electrical chip !), we have replaced the electrical chip by the astro one.

But we observed that the output gain has been reduced to about 3uv/e-.
We have tried a lot of solutions, but no one induced a good result and the
output gain stays at 3uv/e-.

So our question is :  Does the fact of setting Vss at ground (0v), meaning
also that it is at the same potential than output amplifier  load ,affect
the
output gain in so great proportions ?

Since we have obseved the same behavour between the electrical chip and
the two astro ones , is there a great difference between  non coated and
coated chips?

Does coating affect the outpu gain?

We Have found no litterature on the ccd-world forum , about this phenomenon
that is why we send you this mail.

Thank you for your help ,

Best regards.


 -----------------------------
¦ Christian  GUILLAUME
¦ Service Electronique
¦   CNRS / IGRAP                                 Tel: (33).04.92.70.64.09
¦ Observatoire de Haute Provence         Fax: (33).04.92.70.64.64
¦ 04870 St Michel l'Observatoire        Email: guillaume at obs-hp.fr
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