DVCS Calorimeter Trigger System

	Sergey Boyarinov, Stepan Stepanyan, É
	September 2007

DVCS Calorimeter Trigger System Overview

	DVCS Calorimeter Trigger System must search for the clusters produced by photons; normally presence of at least two clusters will be required, although one-cluster or three-cluster trigger must be possible as well
	Cluster is defined as more then N towers (N<=9) with energy deposition above threshold located within 3x3 towers  rectangular area (figure on following slide)
	We assume that CAEN v895B discriminators and v1495 logic unit will be used, although custom logic unit may be designed if necessary

Slide 3

Trigger System requirements

	System takes 424 ECL signals from 27 CAEN v895 discriminators and process them on 5 v1495 logic units as shown on following picture (the number of v1495 units can be increased if necessary; usage of other units is possible)
	System delivers 1 ECL signal to be used as CLAS Trigger Supervisor ASYNC input: level Ô1Õ means ÔpassÕ, level Ô0Õ means ÔfailÕ
	System delivers row number and column number for every cluster found (optional)
	Trigger logic is controlled by following parameters: discriminators thresholds, the number of towers per cluster (from 3 to 9), the minimum number of clusters (one, two or three). Size of cluster search window is fixed and always 3x3 towers.

Slide 5

Time scale

	DVCS Trigger System must be ready by the end of June 2008