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

2. 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?

3. Power Lines

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

5. 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 ?

6. 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

7. 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

8. 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

9. 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

10. 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)

11. 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?