DEIMOS Science CCD Controller

Introduction

The DEIMOS 8Kx8K CCD mosaic is operated using a combination of Bob Leach's SDSU generation 2 boards and UCO/Lick Observatory boards. The SDSU boards include the Timing, Video, Clock, and Utility boards plus a VME interface board that is installed in the data-taking computer. The Lick boards include a Utility Support, Bias and Clock Interconnect, Power and Miscellaneous Signal, and 61-Pin Connector boards that live in the CCD controller chassis. In addition, the dewar electronics boxes contain Lick Analog Switch, Power Filter, and Dual Preamplifier boards. The Lick designed Power Monitor board resides in the separate power supply chassis. Lastly, inside the vacuum chamber are a combination of interconnect boards that adapt the CCDs flex-cables to the hermetically sealed signal and video connectors.
Early in the concept and design phase of the project it was determined that the then current method of wiring the controllers would be inadequate for a mosaic of eight CCDs. At that time we were wiring point-to-point for all internal connections. For a controller of this size and complexity this method would be to slow and prone to errors. It was decided to eliminate as much of the hand wiring as possible. To do this we designed a set of general-purpose circuit boards that would include the major cable connectors and a set of ribbon cable connector for interconnections. The results of the early efforts have provided a solid design that is much less prone to errors. In fact, when the chassis went into testing, the wiring was found to be nearly error free.

The Chassis:

The complement of SDSU boards includes 1 Timing board, 1 Utility board, 5 Clock boards, and 8 Video boards giving a board count of fifteen. A 15-slot VME style back plane is used to interconnect the SDSU boards while leaving enough room to the left of the back plane to mount the Lick Utility Support board. However, due to the number of boards, their power requirements, and the size of the needed power supplies, a separate power supply chassis had to be constructed. The power supply chassis will be discussed later. The new UCO/Lick Observatory boards are used to separate and combine the signals from the SDSU as needed to route them to the proper CCDs. For the most part, the interconnecting cables are ribbon cables. The first set of these cables connect the DB25 and DB35 cables from the video and clock boards to interconnect boards. The video interconnect board breaks up the incoming signals into two output connectors. Each input connector contains 12 bias levels. These twelve inputs are divided into two output connectors of 6 bias levels. Similarly, the 24 clock outputs from the SDSU clock boards are divided into two connectors with 12 clock outputs each. A second type of clock interconnect board is used to break up the 24 signals into eight connectors with three clocks lines each.
The next set of ribbon cables originate on the UCO/Lick Observatory Utility Support board. These eight cables contain the dewar heater lines, temperature sensing lines, a multiplexed bias line and power supply connections. The last ribbon cable is a 64-pin cable that connects the output connector on the front of the SDSU to the input connector on the front of the Utility Support board. A set of 5 small coax cables are used to connect the output of the SDSU Clock board CLK_REF_1 SMA connector to the like connectors on the Lick Utility Support board. Lastly, the power supply wiring consists of the large connectors, PWR1 and PWR2, on the rear of the chassis and the wiring to and from the power distribution terminal strips.

The Boards:

The UCO/Lick Observatory boards consist of a Utility Support board, a 61-pin Connector board, and a Power and Miscellaneous Signal board. The Utility Support board essentially connects the I/O from the SDSU Utility board to the rest of the CCD controller. Functions such as shutter control, Power Monitor board control and monitoring, and the reading back of clock waveforms and bias levels are all connected through this board. The Power and Miscellaneous Signal board routes the Analog Switch Enable signal and power supply voltages to the dewar electronics boxes via two MS-style connectors and the shutter interface signals via a DB15 connector. The boards used to combine all of the signals for the individual CCDs are the 61-pin Connector boards. This board has five ribbon cable connectors that allow different configurations of inputs to be combined and presented to the 61-pin connector that connects to the dewar electronics boxes. This ability to reconfigure the inputs allow for use of different CCD devices and/or different modes of operation by changing only the ribbon cables internal to the CCD controller. There is also a Bias Cable Interconnect board and two types of Clock Cable Interconnect boards. Again, this allows maximum flexibility in configuring the controller.

The Power Supply Chassis:

The DEIMOS dewar has three individual electronics boxes mounted on it. Two of the boxes are associated with the science CCDs and the other with the Flexure Compensation System. Each of the science CCD boxes is mechanically divided into four separate areas, one each for four CCD signal chains. The Flexure Compensation System box is divided into two areas. The separation helps shield the signal chains from each other to lessen the possibility on cross talk. Each chain, both science and flexure compensation, consists of an Analog Switch board and a Pre-amplifier board. The Analog Switch board receives the signal cable from the controller and isolates the pins of the CCD device from any external voltage until the software is satisfied that certain bias and clocks are correct. Once the software has read back the bias levels and verified the clock waveforms it then turns on the switches. The Pre-amplifier board amplifies the CCD video to a level sufficient to send to the controller. In addition to these boards, there is a single Power Filter board in each box that filters and distributes DC power to the other boards.

Inside the evacuated portion of the dewar are ten 61-pin Hermetic connector boards and ten CCD interconnection boards. The hermetic connectors provide the connections for the clocks and biases and the interconnection board adapts the CCD device connections to the hermetic connector board. Lastly, there are three separate hermetic SMB connections for the video to leave the dewar and route into the electronics boxes and to the Pre-amplifiers. For isolation, two SMBs carry the video signals and the third one passes the ground.