1. D. Nelson October 7, 2008 1 Serial Power Overview Presented by David Nelson djn@slac.stanford.edu

2. D. Nelson October 7, 2008 2 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 solutions Must consider in all cases Grounding and shielding System stability Noise performance Segmentation Reliability Transmission line integrity Several high speed protocols use AC coupling CML, LVDS, etc

3. D. Nelson October 7, 2008 3 Serial Power Example Current Regulated Power Source Shunt regulator Series Regulator Two of N Hybrids In series

4. D. Nelson October 7, 2008 4 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 hoses with connector Module 0 Module 1 Hybrid 2 Module 3 Module 4 Module 5

5. D. Nelson October 7, 2008 5 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

6. D. Nelson October 7, 2008 6 Serial Power Advantages (1) Reduced cabling Currents are reduced significantly Component requirements such as connectors and pins are reduced. Smaller volume of services Smaller cables & connectors Reduced Radiation length Smaller wire gauge cables Less PWB copper for power distribution More reliability Less demand for high current connections Better power efficiency Lower currents Doesn’t require switching power supply located near the preamplifiers and detectors.

7. D. Nelson October 7, 2008 7 Serial Power Disadvantages (1) Little/no experience in physics communities. Must AC couple or use fiber communications. Must maintain enough DC balance Insure that data ALWAYS has enough transitions to recover data Use 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 circuitry You 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.

8. D. Nelson October 7, 2008 8 Serial Power Disadvantages (2) High voltage biasing may present issues Detectors 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.

9. D. Nelson October 7, 2008 9 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.