  Increasing luminosity at the Fermilab Tevatron collider has led the D0
collaboration to make improvements to its detector beyond those already in
place for Run IIa, which began in March 2001. One of the cornerstones of this
Run IIb upgrade is a completely redesigned level-1 calorimeter trigger system.
The new system employs novel architecture and algorithms to retain high
efficiency for interesting events while substantially increasing rejection of
background. We describe the design and implementation of the new level-1
calorimeter trigger hardware and discuss its performance during Run IIb data
taking. In addition to strengthening the physics capabilities of D0, this
trigger system will provide valuable insight into the operation of analogous
devices to be used at LHC experiments.
