D_Card  Description
                    -------------------------

                                                  Original Rev. 28-OCT-1996
                                               Most Recent Rev. 26-NOV-1996


General Description:

The D_Card is mounted in the camera electronics.  It provides: The
electronics to receive the digital timing and control lines from the VME
equipment and to send these signals to the TCM2620 array chip and to the
four A_Cards in the camera electronics.

The timing and control signals from the VME equipment arrive on a 17 pair
twist and flat cable as differential ECL signals.  The D_Card terminates
and receives 12 of these signals, and converts them to TTL or CMOS levels.
At this time only 5 timing and control signals are thought to be necessary
to operate the Fast IR Camera.  These are:

   TCM2620 Clock
   TCM2620 Integration Period Clock
   A_Card  ADC Start Conversion Clock (4 copies are made of this signal)

   TCM2620 Mode Control  (Sample time select 10 usec or 100 usec)
   TCM2620 Integration Capacitor Select Control  (11 fF or 102 fF)

The four signals that go to the TCM2620 array are series terminated on the
D_Card and conducted to the array on signal-ground twisted pairs (or else
on miniature coaxial cables).  Thus 8 "wires" penetrate into the dewar to
carry these four signals from the D_Card to the array.  Series terminating
these timing and control signals on the D_Card should work out well because
the TCM2620 array will present only one CMOS load at the end of each of
these twisted pairs.

The ADC Start Conversion clock is received by the D_Card and fanned out
so that there is a separate copy for each of the four A_Cards.  This allows
series termination of these signals on the D_Card and each copy of the ADC
Start Conversion Clock has to feed only a single A_Card.

The 7 spare "channels" on the D_Card are brought out to via's from which
they could be used for other applications as needed.  The unused area on
the D_Card is layed out as a proto-type area.


Power Supplies:

This card receives only Digital power supplies from the VME equipment. In
order to isolate the remote power supplies from the ground structure on
D_Card, the supplies are filter by 15 uH chokes before they are used on
D_Card. The filter inductors are placed on the supply lines, the return
lines, and the sense lines.

The power supplies, located back with the VME equipment, are all remote
sensed on both the four A_Cards and the D_Card.  Because of the series
resistance (about three Ohms) of the small inductors in the sense lines;
the sense signal that is sent back to a power supplies is an "average" of
the potential on the 4 or 5 cards that consume power from that supply.

The power supplies used on the D_Card are +5V Digital, and -4.5V Digital.


D_Card Ground Structure:

The D_Card uses a single digital ground plane and separate +5V and -4.5
Volt supply planes.




General Layout of the  D_Card:
------------------------------


          +-----------------------------------------------+
          |    +---+   +------+   +------+   +------+     |
         +-+   | T |   | Diff |   |      |   |      |    +-+
From     | |   | E |-->|  ECL |-->| CMOS |-->|Series|--->|J|      To
VME      |J|-->| R |   |  Rec |   |Driver|   | Term |    |3|     Dewar
         |2|   | M |   +------+   +------+   +------+    +-+
         +-+   +---+                              |       |
          |             Power Supply Filters      |       |
          |                                       V       |
          |      +-----------------------------------+    |
          +------|                J1                 |----+
                 +-----------------------------------+



J1  2x70   2 row 140 pins total
J2  2x17   2 row  34 pins total
J3  2x12   2 row  24 pins total






D_Card  Timing Signal Pinout:
-----------------------------

  Timing & Control
   Signal Received
     from the VME         Signal Sent    Signal Sent
     Environment           to TCM2620     to ADC's
   J2  Pin Numbers        J3  Pin No.    J1  Pin No.       Signal Name
  ----------------        -----------    -----------   --------------------
    1-2   Term+Rec            N.C.           B36            ADC Clock
     "                        N.C.           B37             "    "
     "                        N.C.           B38             "    "
     "                        N.C.           B39             "    "

    3-4   Term+Rec             23            N.C.       Timing & Control #2
    5-6   Term+Rec             21            N.C.       Timing & Control #3
    7-8   Term+Rec             19            N.C.       Timing & Control #4
    9-10  Term+Rec             17            N.C.       Timing & Control #5
   11-12  Term+Rec             15            N.C.       Timing & Control #6
   13-14  Term+Rec             13            N.C.       Timing & Control #7
   15-16  Term+Rec             11            N.C.       Timing & Control #8
   17-18  Term+Rec              9            N.C.       Timing & Control #9
   19-20  Term+Rec              7            N.C.       Timing & Control #10
   21-22  Term+Rec              5            N.C.       Timing & Control #11
   23-24  Term+Rec              3            N.C.       Timing & Control #12
   25-26  Term                  1            N.C.       Static Signal #1
   27-28  Term
   29-30  Term              All J3 even
   31-32  Term              pin numbers
   33-34  No Connection       are GND.


   Term --> This signal
            pair is
            terminated.

   Rec  --> This signal
            pair is
            received by
            a differential
            ECL receiver.