1. Grounding, Power Distribution
And New Readout Technologies
Excerpts from: US ATLAS Upgrade Workshop
6/7-Jan-2004
SCIPP Seminar 12-Jan-04
Alex Grillo
SCIPP - UCSC
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Grounding, Power Distribution and New Readout Technologies

2. Grounding, Power Distribution and New Readout Technologies
The ATLAS Detector
Largest HEP Apparatus ever built - A general purpose particle spectrometer
One of four LHC detectors
The Inner Detector
ATLAS eTour at
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Grounding, Power Distribution and New Readout Technologies

3. ID Grounding Principles
Sub-detectors are electrically independent (floating power supplies) except for connections to IDGND, the global ID reference point.
All connections to IDGND from sub-detectors are from the EM shields surrounding the detector sections.
Analogue and digital ground referenced on detector modules
Module ground connected to the individual EM shield.
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Grounding, Power Distribution and New Readout Technologies

4. SCT Grounding Layout for Example
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Grounding, Power Distribution and New Readout Technologies

5. SCT Power Distribution for Example
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Grounding, Power Distribution and New Readout Technologies

6. Driving Issues for Grounding Scheme
The grounding scheme keeps a single point ground at the detector and allows the floating power supplies and cable plant to be distributed over a wide area, stretching to USA15 and US15 on either side of the collider hall, without introducing any loops.
For the SCT and Pixels, the control signals to the detector and the data signals from the detector are optical eliminating any electrical interconnects between the Off-Detector DAQ system and the detector.
To minimize any electrical interference between other monitoring systems and the detector, all “slow control” signals are included inside power cabling to the power supplies. Therefore, control signals share the same reference potential and shielding as the detector power.
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Grounding, Power Distribution and New Readout Technologies

7. ID Power Distribution Issues
Power distribution for the ID has two main issues:
Voltage drop from power supplies to electronics
The SCT, for example, currently draws ~1.2A/circuit.
The cable run is ~130m resulting in a voltage drop of about 6V for the 3.5V and 4.0V circuits.
Space for cables, especially through the gap region
All the available space in the gap region is now allocated for existing services.
We are using unusual (i.e. thin insulation) cables in order to fit now.
We will have to be creative to service more channels.
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Grounding, Power Distribution and New Readout Technologies

8. Grounding, Power Distribution and New Readout Technologies
The Voltage Drop Issue
The voltage drop not only wastes power as heat in the cable.
Sudden reduction of current draw (e.g. loss of clock reduces current in digital logic by ~40%) results in large increase in voltage at the detector, possibly exceeding maximum voltage rating of electronics.
SCT now has voltage limiter circuits at PP3 to prevent over voltage in such cases.
This will only become worse with next generation technologies, which operate at lower voltages.
The lower operating voltages of the new technologies can help to lower the power dissipation but that is not enough.
The current requirement also must be maintained or hopefully decreased.
Another option to be investigated is a voltage limiter built into the readout electronics or possibly even on-board voltage regulators.
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Grounding, Power Distribution and New Readout Technologies

9. Grounding, Power Distribution and New Readout Technologies
Cable Volume Issue
The current ID being prepared for installation will fill all the available space available in the gap areas.
If the ID upgrade will increase channel count, we will have to be creative in how we utilize existing cables or existing space.
If current requirements per channel can be reduced, it would be possible to redefine granularity of detector modules/cable.
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Grounding, Power Distribution and New Readout Technologies

10. SCT Cable Passing thru Gap
Pos 1
Quad of insulated wires
2 wires of AWG 20 (power)
2 wires of AWG 28 (sense)
Pos 2
Pos 3
Twisted pair of AWG 28 (500V sensor bias)
Pos 4
Twisted 3 wires of AWG 28 (control)
Pos 5
Pos 6
Drain wire non insulated - 1 wire of AWG 24
Pos 7
Shield of aluminium polyester tape in contact with the drain wire
Pos 8
Outer jacket FRNC
Outer Diameter 5.5mm
Cu for power = 64% total Cu
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Grounding, Power Distribution and New Readout Technologies

11. Development Work is Needed
Some options for power distribution in an all silicon ID:
Replace all TRT services with new services for outer silicon.
Should include some gas lines as well.
Certainly not sufficient by itself.
Reduce current per channel by 2x to 4x to solve voltage drop problem as operating voltages decrease.
Reduce current per channel by 2x to 4x and re-optimize granularity of channels/cable to service more channels.
This will maintain similar voltage drop issue so limiters or regulators must also be developed.
Find added paths for cables to exit ID
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Grounding, Power Distribution and New Readout Technologies

12. UMC CMOS/BiCMOS technology “roadmap” from Paul O’Connor
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Grounding, Power Distribution and New Readout Technologies

13. Technology options from Paul O’Connor
2. Silicon Germanium BiCMOS:
Adding a graded SixGe1-x layer grown by Molecular Beam Epitaxy creates a high-performance npn bipolar transistor which can be integrated with standard bulk CMOS.
The bipolar transistor has excellent high frequency properties (e.g GHz fT), also low current and voltage gain,1/f noise, good radiation resistance, and works at cryogenic temperatures.
This technology is being driven by RF communication and disk-drive markets.
SiGe is a relatively new technology, volume production for the last 4 years. Many of the major foundries (IBM, TSMC) and some smaller ones (AMS) are starting to offer SiGe.
Wafer size smaller than bulk CMOS, costs higher.
More information: J. Cressler’s talk at FEE2003:
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Grounding, Power Distribution and New Readout Technologies

14. Technology Comparison
From the SCIPP Proposal for Advanced Research Development
Estimates by Ned Spencer
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Grounding, Power Distribution and New Readout Technologies