VFAT hybrid and beam board noise studies The measured noise of VFAT2 is very low, at the theoretical level of the design, measured in lab last year. This has been reproduced in H8 for the Roman Pots with and without the silicon detectors. The GEM set-up however has higher noise even without detector. Ground return paths and different powering options have a marked effect on this requiring study.

Roman Pot S-Curve on all channels

RP S-Curve results, VFAT2 without detector Results from S-curve plots Mean Sigma 1.12 Sigma of the sigmas 0.16 Mean of the means 35.81 Sigma of means 0.66 Referring to DAC scan plots Noise over all 128 channels ……….. <ENC> = 589 electrons rms, s = 84 electrons Threshold chosen = 5909 electrons (0.945 fC) Threshold spread over 128 channels = 1.8% (without trimming DACs) This is the measured noise in H8 which is consistent with the theoretical level and lab tests last year.

S-curve results obtained in H8 (without detector) T1/T2 hybrid tests logic DEF3 F0F2 + <s> = 1.3 <s> = 1.8 T2 Beam Board Roman Pot hybrid tests <s> = 1.12 A D A D logic + RP Beam Board BB : Common return, 2 power regulators Hybrid : joined and separate return options tested BB : Common return, 1 power regulator Hybrid : Separate returns

Tests remaining Roman Pot hybrid tests Add second RP board to see if theoretical noise level is maintained. T1/T2 hybrid tests Change Beam board to be identical with respect to powering as RP board to try to achieve the same noise figure as RP. Try to achieve this with multiple hybrids. Only when the set-up is clean and understood without detector can we consider adding the detector in a step by step way to study its effect on the noise. Noise optimisation with the detector includes : Channel capacitance Detector ground return and loops Pick-up/ shielding Power supply and ground impedance and decoupling