The use of content addressable memories in the level 2 trigger for the CLAS detector at CEBAF

The LEVEL 2 trigger in the CLAS detector will find tracks and associate a momentum and angle with each track within 2 micros after the event. This is done through a hierarchical track finding design in which track segments are found in each drift chamber axial superlayer. An array of 384 custom content addressable (or associative) memories (CAMs) uses independent subfield matching to link these track segments into roads. The track parameters corresponding to each found road are then looked up in a separate memory. The authors present the overall architecture of the LEVEL 2 trigger, the details of how the CAM chip links tracks segments to find roads, and report on the performance of the prototype CAM chips