Anti-blooming clocking

[James Beletic]

Dear anti-blooming aficionados,

    I second the questions of Fred Harris, who just asked,

       "Are your "wobble-clocks" bilevel?  RC-filtered analog-switch
        outputs or opamp buffered?  Trilevel antiblooming clocks as
        per Kohley etal's paper from last year's SPIE conference
        (SPIE Vol. 2415 pg 67)?  Mine were RC-filtered complementary-
        VMOS-buffered analog-switch outputs, with little control over
        rise times."

Simon (Tulloch) and Roger (Smith):  Can you explain more what kind of
clock edges were used for anti-blooming clocking?  Could you, or anyone
else, state what you think would be the ideal way to do anti-blooming
clocking?

    I ask because, at ESO, we are now designing a new CCD controller
with this capability specifically in mind.  We plan to have complete
programmability over clock drive voltages, 0.1 volt steps over
+/- 12.8 volts (8 bits), so that we can vary clock edge shape as
required.  That is, have one clock shape for anti-blooming clocking
and another for parallel transfer; perhaps different rising and falling
edges.

    Also, I wonder why a 700 Hz anti-blooming clock is used.  Is this
determined from the maximum charge that can be eliminated on each
clock swing combined with the maximum flux (photoelectrons) expected in
a pixel?  These numbers, if you have them, would be of great interest.

    Happy New Year from foggy cloudy Garching, Germany......it is quite
ironic that we work so hard to build detector systems for stars that
we seldom see.

                                        Best wishes,

                                           Jim



=========================================================================
    James W. Beletic                         E-mail:  jbeletic at eso.org
    European Southern Observatory            Phone:   +49-89-320-06520
    Karl-Sch-Str 2, D-85748 Garching, GER    FAX:     +49-89-320-2362
=========================================================================