Gain measurement with LED and time-over-threshold

passive splitter

LED driver

LED

LVDS out

TDC

ADC

Analog outThreshold L

Threshold H

• It is possible to span different regions of signal amplitude by modulating the charge (voltage and time-width) to the LED (with the CAMAC LED driver)

A small variation in the charge injected into the LED produces a large difference in the produced light (and thus in the signal amplitude)

The intrinsic fluctuation due to the LED alone is very small, compared to the s of the signal due to the gain of the PMT

Original divider

Modified divider

• Reconstruct ToT vs. Q calibration curve using Q from ADC vs. ToT from TDC

Compare two different thresholds:- As expected, higher threshold results in steeper curve

Charge from ADC

Charge from TDC

Charge from ADC given a TDC hit

• Using ToT vs. Q calibration curve reconstruct Q from ToT• Fit gain with usual method

• Fit gain using Q from ADC

• We have seen that is possible to use ToT vs. Q calibration curve to reproduce the gain measurement, for a single crystal

Now we want to:• Produce calibration curve for 1 crystal• Use this curve for several other crystals• Try to reproduce gain with ToT

Setup ready for 6 lead-glasses

• Small problem: find LED’s with similar luminosity(in order to span similar charge/ToT regions)

Farnell Luminosità Vf Produttore Codice produttore1470615 12.5mcd 3.5V Dialight 521-9831F1200581 24mcd 3.8V Forge Europa FNL-U300B01CDSL1200579 34mcd 3.3V Forge Europa FNL-U300B05CDSL1003308 45mcd 4V Avago Technologies HLMP-KB45-A00001200580 70mcd 3.7V Forge Europa FNL-U300B06CDSL1142493 90mcd 4.5V Kingbright L-934MBC1200585 120mcd 3.8V Forge Europa FNL-U300B01WCSL1200583 170mcd 3.3V Forge Europa FNL-U300B05WCSL1470617 310mcd 3.5V Dialight 521-9918F1057128 600mcd 3.6V Marl 1000461712784 1200mcd 3.5V VCC VAOL-3LSBY4