Each Leaf Card accepts up to 36 optical fibres and performs analysis on the data using two Xilinx Virtex-2 Pro FPGAs.

There are three different types of Leaf Card; Electron, Muon and Jet, the nature of the card being determined solely by the firmware.

• The Muon card collates the data from the muon fibres and passes the data to a dedicated concentrator card, where it is compressed and passed to the Global Muon Trigger.
• Each Electron card receives isolated/non-isolated electron data from 9 RCT crates (1 bundle of 27 fibres), corresponding to 1 half of the CMS detector in the z-direction. The card sorts the electron candidates according to rank and selects the four highest rank electrons to be sent to the Global Trigger. The Electron cards are mounted directly on a Concentrator card.
• Each Jet card receives energy sum data from 3 RCT crates (1 bundle of 24 fibres) and perform the 3x3 region sliding window algorithm and transmit the jet lists (central, tau and forward) to the Wheel card for sorting. The jet cards are structured to reflect the geometry of the detector. Each jet card handles one half of the detector in the z-direction and one third of the detector in the f-direction. The cards pass data between themselves in the 'f-direction' to ensure that the edges between regions are handled properly. The Jet Cards also execute the rest of non-electron algorithms and pass all results up-stream to a Wheel card and ultimately to the same Concentrator card as the electron data.

The Leaf Card design is a modified version of a card which has been show work. The jet finder algorithm has been implemented on this card and has also been shown to work.

The Leaf Card is being developed by Magnus Hansen and Matthew Stettler in CERN.