To accomplish this study I have used the detailed modelingtechnique as previously described in the Night Sky Background study(see VERITASftp site, memos subdirectory, file NSB.PS). With thistechnique the individual pulses from both shower and noise (includingafterpulseing) photo-electrons (PE's) are explicitly modeled on a .25ns spacing to achieve the simulated waveform that is expected at theinput to the individual Pixel Constant Fraction Discriminators(PCFD's). The trigger algorithum of the PCFDs is then explicitlymodeled to obtain the trigger time of each pixel. The output logicpulses are then fed into an analog summer and then into theMultiplicity CFD (MCFD) to obtain the 2 fold coincidence trigger. Thistrigger is then used to provide the timing for the ADC gate. The ECLoutputs of the PCFD's are fed to the Pattern Selection Trigger (PST)electronics where in each patch a simple threshold (non CFD)discriminator looks for a 2 fold coincidence (done before the patternsearch is made) which determines the time of the PST trigger. I findfrom the simulation study that the use of the Multiplicity trigger toset the timing of the ADC gate gives a slight improvment over thetiming of the PST trigger. This is especially true if we modify theMCFD to trigger at a fraction of 67% as opposed to the present33%. For proton initiated air showers, with careful attention paid todetermining the arrival time of the pe's at the camera focal plane, Ifind that the 20 ns width of the gate of the ADC's is adequate. Thisis true even for the biggest shower pulses.
In the remaining body of this note I present some of thedetailed results of the study. I want to stress that all the figuresand conclusions in this memo use simulated data only.