Contacted some teams for system GND discussions: cases analyzed are presented here

1. Background • Contacted some teams for system GND discussions: cases analyzed are presented here • Planned to continue with others with the same interactive and practical approach - GNDing is a common (neighborhood) issue - GND is a global (inter)system(s) issue, it should be treated with the knowledge of all possible interfaces between heterogeneous system parts • What needed is a comprehensive schematic diagram with: - detector, electronics, power distribution, signal cables, patch panels, mechanics, etc. - all this for your specific system modularity • Two simple feedbacks: 1) GND is not the solution to all problems: - often GNDing “difficult” because trying to correct other causes through complex GNDing scheme (ex. poor CMRR, instabilities, non linear behavior, insufficient power delivery/poor filtering, etc.) 2) GNDing effort is matter of compromise between system sensitivity and environment noise F. Formenti - ALICE forum 16/03/2006

2. 1 2 4 3 5 1 1 1 2 • Full analog r/o – analog supply (N & P) separate from digital supply (FEROM crate) • Needs special protection up to ADC • Sensitive electronics Hybrid, ALCAPONE and ALABUF • Modularity of 144 half ladders (unless point (4)) • Floating detector - reference points at racks • Relies on ITS support with low impedance to Earth because of points (2) + (3) + (4) left and right Silicon Strips • Shield to provide low impedance Earth connection all the way through from ITS support to racks (both sides) (ITS cones and external alluminazed mylar foil + patch panel boxes + absorber + chariot + space frame + cable trays + racks). As many Earth points as possible • Shield for analog signals insulated from Earth and connected to it at racks (reference point because of FEROM) • Analog shield continuation provided by a number of shielded cables (signal and power) with differential lines; patch panel external box not connected to analog GND but to Earth • “Analog reference” continuation (consequence of FEROM common point) to protect hybrids & flex cables (max 70cm); as clean as possible and insulated from Earth • Symmetrical Common Bias to all half ladder modules referenced at FEROM; floating N and P supplies GNDed at End Cap F. Formenti - ALICE forum 16/03/2006

3. HV PS DET BIAS CAEN EASY PS 2.5V CAEN EASY PS 1.8V 3 6 6 5 4 3 2 1 Silicon Pixels • Full binary r/o • Sensitive electronics limited to half stave (compact layout) • Severe mechanical constraints • Modularity of 120 half staves • Floating PSs - reference point at MCM • GND foil insulated from carbon support CR4 PATCH PANEL R DET DET MCM PIX PIX GND FOIL (INSULATED FROM SUPPORT) CARBON SUPPORT RACKS A & I GND CONNECTIONS OF ONE HALF STAVE • Common reference point for half stave; HV GND connected through a 100kOhm resistor • Floating LVPSs; HVPS is not completely floating by construction • Connection to Earth of ITS carbon support as for SSD (via cones + absorber + chariot + space frame + cable tray) • Twisted (but unshielded) LVPS cables (all signal connections by optical fibers) • Possible only one connection of ground foil to MCM GND • Single Earth connection of GND returns is still to be decided (closest to MCM or at LVPS) F. Formenti - ALICE forum 16/03/2006

4. 2 1 3 4 5 2 6 6 7 6 • Analog electronics on FECs close to detector and ADC • Modularity of ~4500 FECs / 220 RCUs • Local supply regulators; separate analog and digital power • Large r/o surface does not allow “concentrated” reference point • Floating PSs – reference point at each FECs • RCU digital card (not shown) has also floating PSs • Data and trigger through fibers, but Ethernet slow control (transformer less) Time Projection Chamber • Common reference point is FEC/SSW • Floating LVPSs; HVPS GND through resistor to avoid GND loop with ref GND • Connection to Earth of reference GND • Local GND (shortest) for analog circuitry (cooling plate separate GND) • Differential connection between analog and digital parts to avoid GND loop between analog and digital inside FEC • Local VRs to help filtering more noise (see also point (7)) and local capacitors • Untwisted, unshielded power cables (large section) F. Formenti - ALICE forum 16/03/2006

5. 1 1 1 1 2 2 3 4 5 1 3 Slow Controls based on TRD DCS cards & Ethernet • DCSs on very large surface and different systems • No transformer at DCS due to magnetic field • Switch is commercial device • Connection of all the shielding (racks, cable trays, switch bodies, braids of shielded diff lines) together and in all possible Earth points to lower global impedance • Floating PSs • Definition of common GNDs at detector side • Definition of common GNDs at switch side • Separation of different GNDs assured by PHY transformer (important very good quality) F. Formenti - ALICE forum 16/03/2006

6. 1a 1b 1a 2 3 3 4 5 • Analog readout; detector floating (with safety GND); • Very fast analog signal, psec resolution • Modularity of 12 PMTs • Shoebox joining point of two distributed systems and independently powered • Floating PSs – reference point at TRD shoebox • Warning: no differential connection between shoebox and FEE in crate O18 T0 detector 1a) True reference point is at shoebox side: Preamp and TRD digital join here. Also Earth reference is provided 1b) Additional Earth point because of T0 FEE construction (no differential link, case for lowering global impedance) 2) Floating LVPSs 3) Fully shielded power lines all way through 4) Independent resistors on HV returns to avoid signal GND loop 5) HV cables must stay independent (or have their own independent return) all way through, insulated from Earth and are not fully floating at HVPS (HVPS construction) F. Formenti - ALICE forum 16/03/2006

7. 1 4 3 3 2 5 5 TPC/ITS mechanics Earthing SPACE FRAME TPC MUON ABSORBER CHARIOT ITS SSW SSW END PLATE END PLATE SPACE FRAME • ITS suspension points: better if insulated from TPC • Chariot directly GNDed through space frame (not SSW) • TPC outer cylinder in electrical contact with both side end plates • Heating strips (if unused) in electrical contact with TPC inner cones • Connect ITS carbon support to: chariot and absorber F. Formenti - ALICE forum 16/03/2006