Electronics 41 Electronics Design

Herein we describe the CCD electronics. The data acquisition computer is currently a Sun Workstation running Solaris, but will soon be replaced with a rack mounted Linux server. The computer contains an EDT PCI-FOI interface card, which is connected to the CCD electronics via optical fiber. There are two electronics racks, dubbed master and slave, each of which drives one half of the focal plane. Each rack contains its own power supplies. The CCD electronics, which are 6U format, have the following cards: 1) one I/O card in the master rack which contains the EDT fiber interface, 2) one timing generator in the master rack, 3) 9 A/D cards in each rack, 4) 6 driver cards in each rack, and 5) one driver/receiver card in each rack, which drives command and data signals between the two racks. These boards are connected together via a VME-style backplane. From the driver and A/D cards, connections to the CCDs pass via connectors on the backplane to preamplifier cards which are then connected to hermetic connectors via discrete wiring (see Fig. 3). These connections are the only discrete wiring in the system.

Figure 3. Preamp cards. The upper end of each card connects to the electronics rack backplane. The bottom end connects to the hermetic connectors. Each preamp card serves 3 CCDs.

Inside the cryostat, signals travel on custom flex circuits, 3 CCDs per flex (see Fig. 4). Each CCD electronics driver board drives three CCDs. To reduce the number of wires going into the cryostat, we generate the following signals in common for the three CCDs and split them on the flex circuit in the cryostat: S1L, S1R, S2L, S2R, S3, SW, DG, and OG1. The following are generated per CCD: P1, P2, P3, and RD. The following are generated per amplifier: OD, OG2, RG, and, obviously, OS. A thermistor on one of every three CCDs is wired out. The connection from the flex circuit to the CCDs is made by a ZIF connector (Tactic Electronics, model 40-H). Initially we had some continuity problems between the ZIF and the CCD because we did not solder the flex circuit to the ZIF with the two parts flush against each other. This allowed the pins inside the ZIF to move and not lock properly. This problem was completely resolved by resoldering all the ZIFs with the flex circuits flush against the connector body and each pin pulled fully out from the connector as it was soldered.

Figure 4. Flex circuits inside the cryostat. In this figure one of the outer rows of CCDs is already installed and connected. Zener diodes are soldered onto the flex circuit to provide ESD protection.

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