Meeting on Services and Power Supplies Aim: define the services chain form module to external racks

Services Chain Thick power cables d=20mm, l=30m Power Supply DHH Regulation Clock generation Opto transmission Fibres l=30m ATCA Coax, l=30m Thin cable (power) O(1m) Trigger Twisted pair (HF) O(1m) Kapton link ~ 20 cm Module (1/2) Patch panel Repeater (HF) Regulation?

Power Lines

Flex cable – power / bias lines min. copper width (17µm copper) for ∆U < 0.4 V @ 10A: 15 mm total flex width, including digital, bias and sense lines: 24 mm  3 layer flex, 6 mm wide

Voltage drops For high current lines 10 mm² wire, 5Ohm/km: 13.7 mm diameter total cables flex DV (AVDD DCD): 350 mV 350mV DV (DVDD DCD): 130 mV 350mV DV (DHP): 75 mV similar for ground/return Regulation ? Sensing? Clipping? Could increase wire diameter: ½ => 17.5 mm diameter for a cable ?

SVD Grounding DSSD Grounded at EH End-ring hyblid End-ring Repeater -40V Repeater +40V Repeater GND Dock chassis TTM cable CAT5 Grounded at EH GND is taken at single place in Electronics Hut (EH). Sensors for FWD and BWD are electrically disconnected. Two grounds for FWD and BWD become common only in EH. Hybrids are floating (+40 or -40 V), but capacitively coupled to end ring Copper plate in between two hybrids, End-ring, and Dock chassis are connected. No floating metals. (but I don’t remember where the Dock chassis is grounded. tbc) CAT5 shields are grounded at Dock side (EH side must have been disconnected, although there are jumpers to connect on FADCs. tbc). Shield of TTM (trigger, clock and control) cable is used to connect the Mambo (= repeater motherboard in the dock) ground and EH ground. 6

PXD Grounding ? Standard way Ground at +z and –z separated, referenced at PS ? Backplane referenced to a Different (remote) ground Standard way But bulk and backplane connect both halves (at least capacitively) Large ground loop if grounded at PS O(30m) Common ground plane (source) makes it worse PS

PXD Grounding ? PS PS Proposal: local ground and floating PS Ground at +z and –z locally (only few cm apart) , floating remote PS ? Proposal: local ground and floating PS However: where to gound Bulkheads? Carbon structure Special ground plane (there are still small loops, But with signal propagation of O(ns), no noise at low BW (can be avoided) PS PS

Similar problem: current division in wire chambers Anode wires read out at both ends (maybe AC coupled!) Return path via cables to digitizer rack noise, even oscillations Solution: local ground! Short (local) connection of the two ground planes

What to do ? Local ground with floating supplies and I/O Ground loops with noise >100 MHz tolerable Decouple trigger and clock signals -if ladders broken: make sure that they are really disconnected (not even coupled via parasitic capacitance or shorts) -the remote ground at PS seems to be feasible Another problem: electrical contact of silicon bulk to support structure (cooling contact, screw)

Conclusions DHH What determines the maximal distance DHP( or PP) <-> DHH ? What has to go in the DHH? Where to place it (space, radiation, cooling)? Patch panel: Where? (space, radiation, cooling)? What functionality Components? Connectors?