Serial Powering of Pixel Modules

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Serial Powering of Pixel Modules

• T. Stockmanns, P. Fischer, O. Runolfsson and N.
  Wermes

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Why serial powering?
or
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Power consumption

• Every ATLAS - pixel module needs
• 2 supply voltages

Name Voltage Current Power
VDDA 1.7 V 970 1290 mA 1650 2200 mW
VDD 2 V 500 800 mA 1000 1320 mW
Sum ? 1.5 - 2 A
Total detector (1750 modules) 2 V 3500 A
6 power linesper module

• 1 HV bias connection
• 3 ground lines

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Cable
Total distance 152 m Maximum voltage
drop 6.5 V Optimum No cables at all
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Parallel Powering

• For a stave of 13 modules
• power sense lines 104
• supply voltage 2 V / 1,7 V
• supply current 26 A
• power consumption 47 W
• voltage drop 226 W

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Alternative Serial Powering

• For a stave of 13 modules
• power sense lines 2
• supply voltage 26 V
• supply current 2 A
• power consumption 52 W
• voltage drop 65 W

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Pros and Consof both concepts
Parallel Powering Serial Powering
Pros Cons
Individual control of each module Difficult to switch off a single module
No risk for the full chain Risk to loose a full chain
Possible noise crosstalk via power lines
Cons Pros
low voltage high current ? high voltage drop high voltage low current ? low voltage drop
high total power of pixel detector lower power consumption of pixel detector
one power supply per module one power supply per chain
large amount of cables less amount of cables
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Shunt regulators

• 10 shunt regulators built with commercial ICs
• All of them operated in series
• 2 modified to work with the required voltage
• water cooled

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Parallel readout of 2 serially powered modules
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Results of the two modules
Serial powered
Module 1
Module 2
Threshold 4700 e- Dispersion 480 e- Noise
250 e- working pixels 20800
Threshold 4680 e- Dispersion 460 e- Noise
150 e- working pixels 14400
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No influence on module performance
Serial powered
Parallel powered
Threshold 4700 e- Dispersion 480 e- Noise
150e- / 250 e-
Threshold 4330 e- Dispersion 300 e- Noise
148 e-
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Shunt Regulator

• slope of shunt regulators depends on threshold
  and current variation
• higher slope ? better stability
• but higher slope ? more load on lowest regulator

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Shunt Regulator

• slope of shunt regulators depends on threshold
  and current variation
• higher slope ? better stability
• but higher slope ? more load on lowest regulator

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Integration of regulators in newest FE-chip
shunt regulator and linear regulator implemented
and tested in the newest radhard version of the
FE-chip
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Threshold measurement
4 FE-I chips in parallel
1 2 chips in series
Threshold 4680 e- Dispersion 100 e- Noise
264 e-
Threshold 4780 e- Dispersion 105 e- Noise
268 e-
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Serial PoweringSensorless Module

• 13 working chips
• 37120 working pixels

typ. Threshold 4800 e- Dispersion 1340
e- 1200 e- (untuned!) Noise 214 e- 160 e-
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Summary

• Serial Powering of pixel detectors seems to be
  possible
• Feasibility of serial powering proven with
  external regulators
• Regulators implemented into the new radiation
  hard FE-chips
• Internal regulators tested on single chips and
  modules
• electrical performance very similar ? hope that
  the differences in noise disappear with new
  version of regulators
• Next steps
• Using several modules in a series
• Measuring the performance of the modules
  depending on different situations
• Testing possible failure scenarios

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On Module Serial Powering

• On each side of a module the FE-chips are
  connected in series ? Current consumption goes
  down by a factor of 8 with an 8-times higher
  voltage
• Opposite FE-chips are on the same DC-potential

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On Module Serial Powering

• Implementation
• AC-coupling between FE-chips and MCC necessary
• Special sensor design necessary
• Disadvantage
• More complicated module design
• Advantages
• low current consumption
• no risk of loosing a chain of modules
• individual module operation like in parallel
  powering