Acquisition Electronics

A schematic figure of the acquisition electronics is shown in Figure 9. Standard NIM and CAMAC modules are used to extract and digitize the time information from the amplified anode and cathode signals. The time pick-off signals from both the anodes and cathodes are converted to logic pulses by Tennelec model 454 Constant Fraction Discriminators (CFDs). The logic timing signals then travel through 130 ns of delay cables and are regenerated and converted to ECL standard logic pulses by LeCroy model 3412 discriminators. The LeCroy 3412 discriminators have two outputs, one which passes the signal on to the time-to-digital converters (TDCs), and the other which can be used in conjunction with scalar units to monitor signal rates during an experiment. The TDCs are a combination of the LeCroy model 4303 Fast Encoding and Readout TQCs (FERETs) and the LeCroy model 4300B Fast Encoding Readout ADCs (FERAs). The charge output from each FERET is further delayed by 265 ns and fed into a FERA unit, where the signals are digitized and stored until read into the data stream. The FERET units are run in a common stop mode and are gated at the first level trigger rate. The charge outputs are started in the individual channels of the FERETs upon receipt of the timing signal from the LeCroy model 3412 discriminators and are stopped at the end of the gate signal.

  

Figure 9: Schematic of the acquisition and trigger electronics. Only one half of the anode and cathode electronics is shown.

The gates for the FERETs are provided by a LeCroy model 4508 Programmable Lookup Unit (PLU). This unit provides a flexible method of generating a valid event (or gate) signal and can be programmed to accommodate various experimental conditions. The anode signals of the full PPAC array are summed by quadrant (front right, front left, back right, back left) after the CFDs, and these summed signals are the inputs to the PLU. The PLU generates the first level trigger if the conditions for a valid particle event are satisfied. The final trigger requires a coincidence of a valid charged particle event with a selected multiplicity of $\gamma$ rays. This final trigger is used to gate the FERAs and to inform the Gammasphere data acquisition system that the event should be read and entered into the data stream.