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 measurementNeed to assess threshold @sub-mV 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 ADCevaluate LVDS transition time, TL (leading or trailing)assume a trial threshold Vth, evaluate signal transition time TS(Vth)

For the correct Vth value, TL-TS(Vth) is independent of the signal amplitude

Measurement for real signals, use PMT pulsed by 70-ps width LASER source

Threshold measurementTrailing time correlations as a function of trial threshold valuesFor the true value of the threshold, dT should be independent from Vmin

dT (trailing) (ns)

Vmin

Threshold measurement

Correlation factor for trailing times

Vth (V)

Threshold measurementEffect 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 measurementEffect 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 V 3 VV 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 20+-2 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/ms

75 200 325 450V overdrive at comparator

dT = P1 + P2/√Vmax

Preliminary conclusionsFirst 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