FEE card validation M. Raggi, T. Spadaro

The problem Validate FEE production – threshold determination at < 1mV accuracy – comparator time effects: Overdrive Signal slope After validation for prototype cards, final decision for: – amplification – hysteresis – DAC internal pulser features

Threshold Measure threshold by means of time correlation: – fit threshold imposing time response is independent of signal amplitude For this to work, have to evaluate and subtract: – slewing effects – overdrive effects – slope effects

Threshold measurement Measure threshold by means of time correlation: – fit threshold imposing time response is independent of signal amplitude For this to work, have to evaluate and subtract: – slewing effects – overdrive effects – slope effects

Threshold measurement Need to assess level, mandatory for Q vs T reliability Tried measuring efficiency as a function of minimum signal voltage: would need clean environment: in presence of a 2-3 mV radiofrequency noise, width of efficiency profile depends on noise Try to overcome this, by measuring crossing times: register both a signal copy and the LVDS output with a flash ADC evaluate LVDS transition time, T L (leading or trailing) assume a trial threshold V th, evaluate signal transition time T S (V th ) For the correct V th value, T L -T S (V th ) is independent of the signal amplitude Measurement for real signals, use PMT pulsed by 70-ps width LASER source

Threshold measurement Trailing time correlations as a function of trial threshold values For the true value of the threshold,  T should be independent from V min  T (trailing) (ns) V min

Threshold measurement Correlation factor for trailing times V th (V)

Threshold measurement Effect of overdrive-dependent delay at the comparator must be subtracted for dT to be independent on Vmax Reminder: for old (new) voltage at comparator is amplified x5 (x3) wrt original signal

Threshold measurement Effect of slope-dependent delay at the comparator must be subtracted for dT to be independent on Vmax Reminder: for old (new) voltage at comparator is amplified x5 (x3) wrt original signal 1 V 2 V3 V V equivalent at comparator for 5 ns rise time ~ 0.2 V

First assessment of overdrive + slope effects Reminder: for old (new) voltage at comparator is amplified x5 (x3) wrt original signal Measure via CAMAC LED driver pulser FEE threhold was mV Can vary signal amplitude: range used, from 30 mV to 200 mV Presently, cannot vary rise time: fixed at ~ 2.7 ns (20%-80%) vs PMT value of ~ 5 ns. For 30 mV, this is equivalent to ~ 8 V/  s V overdrive at comparator  T = P1 + P2/ √ V max

Preliminary conclusions First assessment of overdrive + slope effects seem satisfactory for veto capabilities Have to confirm this picture with smaller slope, as for the PMT signal Will use again ultra-short LASER pulse + PMT to measure combined effect For the mass validation, 2 possible methods might be performed: 1.Use of LASER + PMT, including step-by-step motor for LASER intensity automatic variation 2.Use of a GPIB-programmable pulser, for which both amplitude and rise time can be changed