D. NelsonOctober 7, 20081

Serial PowerOverview

Presented by

David Nelsondjn@slac.stanford.edu

D. NelsonOctober 7, 20082

Serial Power

Serial power is a viable option but…Must be evaluated on a system by system basis.

There are always advantages and disadvantages for different solutionsMust consider in all cases

Grounding and shieldingSystem stabilityNoise performanceSegmentationReliabilityTransmission line integrity

Several high speed protocols use AC couplingCML, LVDS, etc

D. NelsonOctober 7, 20083

Serial Power Example

Current RegulatedPower Source

Shunt regulator Series Regulator

Two ofN

HybridsIn

series

D. NelsonOctober 7, 20084

Six-module stave (finished; LBNL/RAL)

-operating reliably with multi-drop control/command cables

-Low noise despite some compromises

-Can run from a single HV line

Interface PCB Cooling hoseswith connector

Module 0

Module 1

Hybrid 2

Module 3

Module 4

Module 5

D. NelsonOctober 7, 20085

30-module stave (LBNL)

might become the largest serial powering stave ever built

so far looking very good in terms of SP

4 V x 30 hybrids = 120 V (0.8 A)

In future systems: 1.5 V x 20 hybrids = 30 V

6-chip hybrid with SP on 3 cm long silicon sensors

Chain of 30 hybrids is working fine

Module stave is being built up

D. NelsonOctober 7, 20086

Serial Power Advantages (1)

Reduced cablingCurrents are reduced significantly

Component requirements such as connectors and pins are reduced.

Smaller volume of servicesSmaller cables & connectors

Reduced Radiation lengthSmaller wire gauge cablesLess PWB copper for power distribution

More reliabilityLess demand for high current connections

Better power efficiencyLower currents

Doesn’t require switching power supply located near the preamplifiers and detectors.

D. NelsonOctober 7, 20087

Serial Power Disadvantages (1)

Little/no experience in physics communities.Must AC couple or use fiber communications.

Must maintain enough DC balanceInsure that data ALWAYS has enough transitions to recover dataUse 8b-10b or other encodings schemes.

Need to consider coupling capacitors’ stored energy.Ensure that power up, power down, and fault conditions don’t destroy electronics.

Minimize coupling capacitor sizes.

Should include ground fault circuitryYou want all of the current going through the intended electronics and not taking a short cut.Sections of electronics are tens of volts from detector grounds.

D. NelsonOctober 7, 20088

Serial Power Disadvantages (2)

High voltage biasing may present issuesDetectors will see different biasing if using a common external HV source

Could develop HV locally on the serially powered section

Not all that easy developing clean HV without iron core inductors.

An open could occur that acts much like the series Christmas tree light failure.

D. NelsonOctober 7, 20089

Conclusions

Need to take a close look at requirements to see if serial power is appropriate.

Serial power can work.We have some operational experience at LBNL on silicon strip detectors. (slide 5)

No hybrids broke during many power cycles to date

Noise performance is good.

AC coupling of LVDS works.