P. Aspell CERN April 2011 CMS MPGD Upgrade …. Electronics 2 1

P. Aspell CERN April 2011 LHC-Upgrade style readout system The GBT is currently foreseen for many LHC upgrades : CMS tracker, HCAL, Atlas tracker, LHCb (all upgrades) Generic projects in CERN for : DC/DC Powering GBT Versatile Link Front-end detector module FE ASIC E-link FE ASIC E-link Clock, T1 commands FE Trig, Data GBT Elinks 80, 160 or 320 Mbps (40, 20, 10 Elinks/GBT respectively) Optical 3.2Gbps FE ASIC E-link Counting room Interface and driver board Ser/Des Trigger DAQ DCS TTC Power 2

P. Aspell CERN April 2011 CMS MPGD upgrade electronics 3 GBT Front-ends VFAT/GdSP DC/DC converters Power Supplies LV HV ~10V Optical 3.2Gbps Interface and driver board Ser/Des Trigger DAQ DCS TTC Counting room GLIB (Gigabit Link Interface Board)

P. Aspell CERN April 2011 CMS MPGD upgrade electronics 4 GBT Front-ends VFAT/GdSP DC/DC converters Power Supplies LV HV ~10V Optical 3.2Gbps Interface and driver board Ser/Des Trigger DAQ DCS TTC Counting room GLIB (Gigabit Link Interface Board) F. Faccio/ G. Blanchot et al. P.Moreira et al. F. Vasey et al. P.Aspell et al. P.Vichoudis et al. R. De Oliveira GEM

P. Aspell CERN April 2011 CMS MPGD upgrade electronics meeting 2 Focus on GEM electrical design 5 GBT Front-ends VFAT/GdSP DC/DC converters ~10V Optical 3.2Gbps Discussion points for ultimate goals : Power delivery through the GEM to the VFATs with a star point ground ? How many electronic routing planes? Routing of e-links from the front-ends to the GBT on the GEM? 3 pairs (SLVDS) per front-end. Packaged front-end verses hybrid. Electronics board for the GBT and dc/dc converter. A plug-in or directly on the GEM ?

P. Aspell CERN April 2011 Common mode issues with GEMs Coupling within the detector Return paths, Grounding and shielding Measurements in Totem T2 and in the MPGD lab show the minimum threshold is different between detectors and higher than it should be. There appears to be a high level of common mode pickup. Detailed studies on-going in these two areas both in the lab and via simulation. Aim : to arrive at proposals for improvements in : 6 Detector designGrounding, return paths and shielding Front-end design : VFAT3 GDSP Readout

P. Aspell CERN April 2011 Problems with existing systems : Potential common mode path – to be avoided HV 0V -ve VFAT chip vddavddd gndagndd gnddet Problem : If hybrid A connector is higher impedance than hybrid B connector then circuit return current would be forced through the gndDet route creating common mode noise on A. VFAT chip vddavddd gndagndd gnddet LV power and Signal path A B

P. Aspell CERN April 2011 Problems with existing systems : Ground loops !!! HV 0V -ve VFAT chip vddavddd gndagndd gnddet VFAT chip vddavddd gndagndd gnddet LV power HVLV Here there are ground loops everywhere which can cause problems. There is no distinction between Ground, Return Paths, Shielding. Faraday cage

P. Aspell CERN April 2011 Guidelines : Return currents and shields. No ground loops on GndDet Avoid circuit currents in GndDet. Minimise other ground loops, preferably to zero. No current flow in Faraday Cage (Shield). Minimise impedance of power and return line paths and connectors.

P. Aspell CERN April 2011 Options : 1 thick return path HV -ve VFAT chip vddavddd gndagndd gnddet ✓ No current in detector shield ✓ No ground loops ✓ Low impedance gnddet and gnda ✗ Analog return currents are in series and could cause common mode unless it is very low impedance. VFAT chip vddavddd gndagndd gnddet Signal path only Power Very low impedance connection between hybrid and return plane. Notes : The LV power is delivered via a power connector on the GEM not to individual hybrids. The gnda and gndd should be separated on the hybrid.

P. Aspell CERN April thick return paths HV -ve VFAT chip vddavddd gndagndd gnddet ✓ No current in detector shield ✓ No ground loops ✓ Low impedance gnddet and gnda ✗ Analog return currents are in series and could cause common mode unless it is very low impedance. VFAT chip vddavddd gndagndd gnddet Signal path only Power Very low impedance connection between hybrid and return plane. Notes : The LV power is delivered via a power connector on the GEM not to individual hybrids. The gnda and gndd should be separated on the hybrid.

P. Aspell CERN April 2011 Separate gndDet HV -ve VFAT chip vddavddd gndagndd gnddet Notes : The LV power should be removed from the signal path flat cables. The gnddet, gnda and gndd should be separated on the hybrid (requires new hybrid). The gnddet should be run as a star connection. The gnda and gndd could be run as common ground planes between chips. VFAT chip vddavddd gndagndd gnddet Signal path only Power connector Very low impedance connection between hybrid and return plane. No current in shield. The return current of one chip can only affect itself not others. No ground loops, the gnddet return is a star configuration with the star point at the power connector. Gnda circuit current cannot flow in gnddet. ✓✓✓✓✓✓✓✓

P. Aspell CERN April 2011 Regulators on the detector HV -ve VFAT chip vddavddd gndagndd gnddet VFAT chip vddavddd gndagndd gnddet Signal path only HV An. And Dig. Reg.s LV

P. Aspell CERN April 2011 General remarks on common mode studies so far. The minimum threshold problem is higher than it should be due to common mode. Small improvements have been made in the lab by eliminating ground loops and providing separate power supply. The min threshold is fine when VFAT is unconnected from the detector irrespective of the hybrid ground connection ie. If gnda and gndd are connected together. Separating gnda and gndd on the hybrid makes the noise worse in all configurations looked at. IComp : Reducing IComp helps a lot. This reduces a 30uA/channel comparator switching current. Error discovered on hybrid due to bonding. Comparator O/P stage current is bonded to the analog instead of the digital return. Desirable design improvements to existing systems: separate power delivery, new hybrid with better connectors, better cables, electrical isolation from readout board ??

P. Aspell CERN April 2011 VFAT front-end GndDet GndA GndD

P. Aspell CERN April 2011 Signal currents for ideal 12fC input charge Comparator output voltage GndDet Signal return current ~4uA peak ~0.5mA if all channels fire together GndA Analog return current ~25uA peak change (~3.2uA all channels fire together) Gndd Digital current ~ 30uA movement (3.8mA if all channels fire together)

P. Aspell CERN April 2011 For today Brainstorm on how to implement these ideas in the forthcoming prototypes in terms of detector design and hybrid design.