[Hps-ecal] Preamplifiers Gain

[Raphaël Dupré]

Hello Everyone,

Following on Stepan question about PA gains during last meeting, here is 
a summary of PA gains settings.

CLAS IC Pre amps gains were set at 2333 pC/pC and 3 V/pC (calculated 
with 20ns input pulse width)

The new gain is 0.63 V/pC (calculated with 10ns pulse width) the reason 
for the change are the change in surface (factor 4) and the reduction of 
the pulse width. We use this new pulse width because Andrea's 
measurements shown that they are more relevant. That makes ~20% 
reduction of the gain if I remember correctly numbers I seen from 
Gabriel (mind that is NOT a change on the PA, but a change of the way we 
measure its characteristics). In conclusion the gain in V/pC has been 
reduced by roughly a factor 4 to account for the larger APDs +- small 
adjustments since we recalculated everything from scratch.

In pC/pC the new gain is 224 pC/pC, i.e. a factor 10 reduction. You can 
already account for a factor 5 as for the gain in V/pC described before. 
Then you have to add the reduction of the output pulse width. When 
reducing the output pulse width by a factor two you have to drop by a 
factor 2 the gain on the integrated charge to conserve the gain in V/pC.

I hope things are now clearer on the settings for the PA. In any case, 
Emmanuel will give a detailed talk on the PA in our ECal weekly meeting 
soon! (Probably the 14th)

Best regards,

-- 

Raphaël Dupré
Institut de Physique Nucléaire d'Orsay
Université Paris-Sud