The Pickoff Card

Figure 1. The new pickoff card, labeled.

The "pickoff card" attached to the SBX of each detector receives the single-ended signals for the Ge Center, Ge Sides, and BGO segments from the Slope Box. It converts these to differential signal format before sending them to the rest of the DAQ system. The pickoff card was made from an FPGA-based design that provides a communication hub interfacing the preamp, power board, dongle and slope box to EPICS through a serial interface. Its analog signal paths are completely software controlled - new signal combination modes now enable new measurements. The new pickoff card automatically scans and collects data from the slope box, preamp, power board and dongle into dual-port memory so entire detector appears as one interface to the IOC, and implements data logging/histogramming memory for monitoring of various system parameters (preamp reset rate, detector voltages, etc.)

Figure 1 shows the pickoff card, a circuit board with sections allocated to each of its functions. Parts of the pickoff card are dedicated to the processing of specific signals, like the Ge center, Ge sides, and BGO sum and BGO pattern. It is designed to stack up with the SBX power board, and has protruding connectors on two different sides to do so.

The VXI Pickoff Card (Before Upgrades)

The large 50-conductor grey cables ran between the Slope Box on each detector to the Pickoff cards in the VXI crates. The VXI Pickoff Card received the single-ended signals for the Ge Center, Ge Sides, and BGO segments from the Slope Box. The VXI pickoff converted them to differential signal format before sending them to the digitizer. Signals had to be sent to the shack to be converted and conditioned in the previous system.

Figure 2. The VXI system, with old pickoff cards at the end of cables.

VXI Pickoff Card Features

• Three gain range options (jumper selectable from the bottom of the pickoff card) for the Ge Center: 2, 5, 10 MeV

• There was a fixed Preamp Reset Clamp that drove the Ge Center back to baseline after a preamp reset. They sometimes had oscillation problems (ringing) that could hinder resolution.

• There was an analog output on the VXI board. This LEMO output was shaped similar to a NIM Spectroscopy Amplifier, and was NOT what gets sent to the digitizer.