Compilation of Dis-/Advantages of DC-DC Conversion Schemes Power Task Force Meeting December 16 th, 2008 Katja Klein 1. Physikalisches Institut B RWTH Aachen University

Advantages: Grounding Katja Klein2Discussion of DC-DC Conversion Standard grounding scheme  Module ground potentials are all the same  Common ground reference for bias, analogue and digital voltage for whole substructure (rod, petal)  Bias voltage ground reference is the same for all modules  Easier for slow controls (difficult in SP to sense voltages)

Advantages: Communication Katja Klein3Discussion of DC-DC Conversion Readout and control scheme is very standard  AC-coupling of communication not needed  Control chips can be supplied independently of modules

Advantages: Start-Up & Selective Powering Katja Klein4Discussion of DC-DC Conversion Easy start-up  Control chips can be powered on first  If one converter per module, single modules can be powered on/off  In scenario w/ charge pump per chip, single chips can be powered on/off

Advantages: Different Voltages Katja Klein5Discussion of DC-DC Conversion Different voltages can be provided  Buck-type converters: the same converter chip can be configured for different output voltages  Via a resistive bridge  Two conversion steps can be combined  No efficiency loss (in contrast to linear regulation in SP)  Can cope with V opto > V chip  Can cope with V ana ≠ V dig  Charge pumps: only integer conversion ratios, defined by configuration

Advantages: Flexibility Katja Klein6Discussion of DC-DC Conversion Great flexibility with respect to  combination of modules with different load  Different numbers of readout chips  Trigger modules vs. standard modules  power groups with different number of modules  TEC vs. barrel In contrast, with SP current is fixed to highest current needed by any chain member  chains must be uniform to avoid burning power in regulators

Advantages: Changing Loads Katja Klein7Discussion of DC-DC Conversion Compatibility with changing loads, relevant for  pixel detector  load is driven by occupancy  trigger modules SP: the highest current potentially needed must always be provided  inefficiency

Disadvantages: Chip Technology Katja Klein8Discussion of DC-DC Conversion Need for a “high voltage“ tolerant process (10-12V)  Good candidate identified, radiation hardness still to be proven  Strong dependency on foundry: support of process over years?  Any changes in process must be followed closely and irradiation tests be repeated

Disadvantages: Converter Efficiency Katja Klein9Discussion of DC-DC Conversion Converter efficiency will be around 80% (ESR of passive components, R on of transistors, switching losses)  Local generation of heat  cooling of DC-DC converters needed  Local efficiency decreases with lower conversion factor (U out /U in )  Local efficiency decreases with higher switching frequency  In two-step schemes efficiencies multiply

Disadvantages: Currents in Cables Katja Klein10Discussion of DC-DC Conversion Cannot compete with Serial Powering  Currents in power group with DC-DC conversion = I 0  n  r  I 0 = current of a single module  n = number of parallely powered modules in the power group  r = conversion ratio = U out /U in  Current in Serial Powering chain = I 0, independent of n  E.g. for 20 modules in power group need r = 20 to compensate  Higher efficiency in SP (at least up to FE)  less cooling needed  Cables inside tracker volume can be thinner with SP

Disadvantages: Risks Katja Klein11Discussion of DC-DC Conversion We have to stick with parallel powering  Multiplicity (modules per cable) as today or higher  Open connections (e.g. at PP1, PP0) lead to loss of power group  Short on module leads to loss of power group  Protection needed? Use DC-DC converter to switch off module?  Converter can break: can imagine isolated failures (loss of regulation...) and failures that lead to loss of power group (short)  More risky if one converter powers several modules  Do we need redundancy?  This adds mass

Disadvantages: Material & Space Katja Klein12Discussion of DC-DC Conversion Material budget and space considerations  Amount of copper in cables scales with current = I 0  n  r  I 0 = current of a single module  n = number of modules in the power group  r = conversion ratio = U out /U in  Air-core inductor (even if integrated into PCB, it needs a lot of copper)  Filter capacitors, maybe other filter components  With regulation (buck etc.), PCB traces can be narrow  Without regulation (charge pumps), input voltage must be exact  Linear regulator or rather solid input traces  Is shielding needed? How to design good low mass shielding?

Disadvantages: Material Budget Katja Klein13Discussion of DC-DC Conversion Simulated components: Kapton substrate with 4 copper layers Copper wire toroid Resistors & capacitors Chip FE-hybrids Kapton circuits Analog Opto- Hybrids Mother- boards TEC 1 converter / module

Disadvantages: Material Budget Katja Klein14Discussion of DC-DC Conversion Strip tracker Total gain for strip tracker with 1 converter per module and a conversion ratio of 8; with power cables and motherboards modified accordingly:

Disadvantages: Noise Katja Klein15Discussion of DC-DC Conversion DC-DC converters are undoubtedly noise sources (by design)  Conductive noise through cables  Ripple on output voltage: switching frequency (1-5MHz) + higher harmonics are in the bandpath of the amplifier  Switching leads to high frequency noise (tens of MHz, not so critical)  Both CM and DM contributions  Radiated noise  From inductor near field via inductive (and capacitive?) coupling  From cables  Has to be taken into account for all aspects of electronics system design: readout chip, FE-hybrid, grounding & shielding, motherboard, layout...  Not clear what to prepare for: noise depends on implementation  For same chip, noise emission can be rather different depending on PCB etc.  Scalability from lab system to complete detector not obvious  PS noise requirements to be understood