P. Aspell CERN April 2011 1

CMS MPGD Upgrade …. Electronics 2

P. Aspell CERN April 2011 2

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

E-link

Clock,T1 commandsFE Trig, Data

GBT

Elinks80, 160 or 320 Mbps(40, 20, 10 Elinks/GBT respectively)

Optical link @ 3.2Gbps

FE ASIC

E-link

Counting room

Interface and driver board

Ser/Des

Trigger

DAQ

DCS

TTC

Power

P. Aspell CERN April 2011 3

CMS MPGD upgrade electronics

GBT

Front-endsVFAT/GdSP

DC/DC converters

Power SuppliesLV

HV

~10V

Optical link @ 3.2Gbps

Interface and driver board

Ser/Des

Trigger

DAQ

DCS

TTC

Counting room

GLIB(Gigabit Link

Interface Board)

P. Aspell CERN April 2011 4

CMS MPGD upgrade electronics

GBT

Front-endsVFAT/GdSP

DC/DC converters

Power SuppliesLV

HV

~10V

Optical link @ 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 OliveiraGEM

P. Aspell CERN April 2011 5

CMS MPGD upgrade electronics meeting 2Focus on GEM electrical design

GBT

Front-endsVFAT/GdSP

DC/DC converters

~10V

Optical link @ 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 6

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 :

Detector design Grounding, return paths and shielding

Front-end design :VFAT3GDSP

Readout

P. Aspell CERN April 2011

Problems with existing systems :Potential common mode path – to be

avoided

HV0V

-ve

VFAT chip

vdda vddd

gnda gnddgnddet

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

vdda vddd

gnda gnddgnddet

LV power and Signal path

A

B

P. Aspell CERN April 2011

Problems with existing systems : Ground loops !!!

HV0V

-ve

VFAT chip

vdda vddd

gnda gnddgnddet

VFAT chip

vdda vddd

gnda gnddgnddet

LV power

HV LV

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

vdda vddd

gnda gnddgnddet

✓ 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

vdda vddd

gnda gnddgnddet

Signal pathonly

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

2 thick return paths

HV-ve

VFAT chip

vdda vddd

gnda gnddgnddet

✓ 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

vdda vddd

gnda gnddgnddet

Signal pathonly

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

vdda vddd

gnda gnddgnddet

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

vdda vddd

gnda gnddgnddet

Signal pathonly

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

vdda vddd

gnda gnddgnddet

VFAT chip

vdda vddd

gnda gnddgnddet

Signal pathonly

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

GndDetSignal return current ~4uA peak~0.5mA if all channels fire together

GndAAnalog return current ~25uA peak change (~3.2uA all channels fire together)

GnddDigital 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.