Grounding and Shielding of CMS Endcap Muon on-chamber
electronics.
N. Bondar, B. Bylsma, S. Lusin, A. Madorsky, P. Robl, V. Sedov.
This document describes the current implementation of the grounding and shielding on the
existing chamber prototype.
Ideally, all the electronics should be enclosed into one giant Faraday cage, as described in
[1]. In practice, however, this approach is sometimes problematic, and some violations are
unavoidable. In case of the ME234/2 prototype, which is working in Lab 7, the following
guidelines were used in implementation of grounding:
1. Cooling plate (thick aluminum plate with embedded water pipe) is used as a solid
ground for all on-chamber electronics.
2. Cooling plate is connected in many points to the chamber frame forming common
ground with chamber cage.
3. All electronics is connected to cooling plate in the carefully selected points to
avoid ground loops.
4. All boards are under metal covers forming Faraday cages (to some extent).
5. Al cables (including power) are shielded, and the shields are connected to ground.
Fig. 1 shows the physical layout of the on-chamber electronics. Only wide end of the
chamber is shown. The cooling plate is attached to the chamber near the wide end, and its
form repeats the form of the chamber. Five Cathode Front-End boards (CFEB) are situated
along the chamber’s wide end to minimize the length of the cables carrying analog signals
from the cathode connectors. 24 Anode Front-End boards (AFEB) are connected right to
the anode connectors along the “Anode” side of the chamber. The output of these boards
in LVDS format is sent to Anode Local Charged Track (ALCT) board. As one can see, all
analog signals are digitized right on the chamber, and only digital signals are transmitted
away. This significantly reduces the risk of parasitic pickup introduced into chamber’s
output.
All the digital signals from the chamber are transmitted into peripheral crate in LVDS
standard.
AFEB – Anode Front-End Board.
Grounding of the AFEB is provided by the aluminum cover attached to the board from the
component side. This cover consists of two parts, one of which is right-angled and
attached to the chamber side aluminum cover with two screws. The solder side of AFEB
has grounded copper pour, which with the component side cover creates the structure
similar to Faraday cage but open on the edges.
The input connector of AFEB is connected directly to the anode connectors, eliminating
the cable carrying analog signal.
Fig. 1. Chamber integration drawing showing all the boards and connections. See text
below for details and abbreviations.
Fig. 2. On-chamber electronics grounding schematics1.
1
For types of cables, see document [3].
Digital ground
DGND
Cables
#13. LV
power
Cables
#14. LV
power
Cables
#13. LV
power
5V
2 .5 V
3 .3 V
AGND
DGND
- 4 .3 V
6V
5 .5 V
LVD B
Linear regulator
Chamber frame / cooling plate - reference ground.
Chamber's internal "clean" ground
Board enclosure
Analog ground
AGND
DC-D C (off
cham ber)
5V
3 .3 V
6V
3 .3 V
2 .5 V
5 .5 V
- 4 .3 V
6 Coaxial cables
#8 from test
strips
From HV power supply
with f loating output.
Cables #9.
LV power
DGND
AGND
ALC T
Cables #6.
LV power
5 .5 V
5 .5 V
LVDS
CFEBs - 5 bo ards
Cables #7
LVDS
LVDS JTAG
LVDS JTAG
LVDS
LVDS
Possible connection
to chamber frame.
DGND
AGND
LVDS
LVDS
16 analog signals
16 analog signals
Cable #4
To/from DQMB
Cable #5
to/from
CLCT
6 cables #2 for each
board
From cathode
connectors
From anode connectors.
There are no cables,
AFEBs are connected
direct ly to anode
connectors.
16 analog signals
AFEBs - 24 b oards
Cables #10 to Slow
control
Cable #12 to DQMB
Cable #11 to TMB
Multiconductor HV
cable #1.
Output digital data in LVDS format are sent to ALCT thru the cable #7. Braid of this cable
is connected to one of the screws holding the AFEB cover.
AFEB has two grounds - "input ground" - connected to the "internal ground" of the
chamber - and "output ground" (cooling plate, frame and the chamber side covers joined
together with screws). "Internal ground" on the chamber is formed from the chamber solid
cathodes, external copper screen and copper ground jumpers on the anode and cathode
outlets sides.
Cable braid
connected to the
screw
Screw
Chamber
side cover
(output
ground)
AFEB cover
Standoff
Cable #7 to
ALCT
Output/Power
connector
Component
Board with
copper pour
on the bottom
Fig.3. AFEB grounding.
Aluminum
cover
Cable
holder
3 cables
#7 to
ALCT
Aluminum
cover
holder
AFEBs
See fig. 3 for
details
Chamber side
cover
Fig. 4. Aluminum cover protecting AFEBs.
Input connector
(carries internal
chamber
ground)
These two grounds are connected together in the signal outlet sides (the best position,
determined experimentally). The output cables #7 transport digital signals, so this cable
ground is connected to the "output ground" of the chamber (see Fig.3).
There is an additional cover enclosing all AFEBs. The main purpose of this cover is to
protect AFEBs from mechanical damage, but it also serves as an EMI shield improving
the noise situation.
Cable
#7 to
ALCT
AFEB
Aluminum
cover
Aluminum
cover holder
Fig. 5. View of 3 AFEBs, cables #7 to ALCT, aluminum cover and its holder.
CFEB - Cathode Front-End Board.
The CFEB board ground plane is connected to the chamber ground primarily through the
low impedance braided shield of the CFEB input cables. One end of the shield is
connected to a spade terminal soldered to the cathode ground plane. The other end is
connected to a spade terminal soldered to the front-end (analog input end) of the CFEB.
There are six input cables for each CFEB ranging in length from about 16 cm to about 30
cm. In addition, the board ground plane is connected to the Faraday shield through two
mounting holes screwed to the cooling plate, which serves as the bottom of the Faraday
cage. The two grounded mounting holes are located at the analog front end of the CFEB.
There are other mounting holes on the CFEB but they are not grounded in order to avoid
additional current paths to the analog front end. It should be noted that the cooling plate
does not provide a low impedance path to the chamber ground and it should not be used
for this purpose.
Digital
ground
InterCFEB cable
#3 to next CFEB
Analog
ground
Grounding
points
Input cable #2
from the
cathode
connectors
Output cable
#4 to DMB
Output
cable #5
to CLCT
Power
cable #6
from
LVDB
Grounding
contacts
Fig. 6. CFEB grounding and connectors.
Each chamber has five CFEB’s. Each CFEB is enclosed in its own Faraday cage. The
Faraday cages are formed by the cooling plate on the bottom, aluminum “C” bracket
partitions on the sides, and a common cover over all five CFEB’s. The current prototype
cover has openings to allow the CFEB connectors to extend outside the cover. Future
covers will be extended and have small slots just large enough to allow entry of the cables.
Partition
Power
Output cables
and connectors
Partition
Input cables
and connectors
Fig. 7. CFEB board installed on chamber. Cover is removed.
Wide end of
the chamber
Fig. 8. CFEB cover installed.
Cable braid
attached to
spade
terminal
Fig. 9. Analog cable connection to the input connector of CFEB.
Cable braid
attached to
spade
terminal
Fig. 10. Analog cables #2 attached to the connectors.
ALCT – Anode Local Charged Track board.
ALCT also has ground plane split into analog and digital part. There is the Main
Grounding point right in the splitting point, and theoretically, the board should be
connected to the cooling plane only in this point. However, in practice the best result is
achieved when all four corners of the board are grounded also.
The digital LVDS cables #7 run from AFEB output connectors to 24 input connectors of
the ALCT. Braids of these cables are grounded at AFEB (see AFEB section) and ALCT
using spade terminals, providing good EMI shielding.
Currently, only digital part of ALCT is covered with EMI shield. Later the shield will be
modified to cover all ALCT.
Power cable #9
from LVDB
2 JTAG cables
#10 to Control
Module
testing
connector
cable #11
to
DAQMB
Digital part
Main grounding point
Ground splitter
Analog part
24 cables #7
from AFEBs
6 cables #8
from test strips
24 spade
terminals for
AFEB cable
braid connection
Fig. 11. ALCT connections.
cable #12
to TMB
Cables #7
from
AFEBs
Fig. 12. ALCT with EMI shield installed.
LVDB – Low Voltage Distribution Board
LVDB converts the incoming low voltage power (+6.5 V analog and digital, -5.5V
analog) into the voltages necessary for all other on-chamber boards. LVDB is grounded
thru the output cable’s return wires (see Grounding Schematics Fig. 2) to avoid ground
loops. Input voltages are supplied by Vicor DC-DC converters. The outputs of DC-DC
converters are floating, so they are also grounded only thru the return wires.
The power cables’ shields are connected to the return lines on the LVDB and they are not
connected at the CFEB and ALCT end. In Chuck Rush and Ben Bylsma’s opinion this
configuration is not the best way to connect the shields, and although it is working fine
now at Fermilab, it may not in another environment. However, for future LVDB boards
the shield should optionally be connected to the cooling plate through the mounting holes.
There is an EMI shield cover for LVDB as well. It encloses all the board and attaches to
the partitions on both sides of LVDB.
Cable #6, power to CFEBs
Cable #15
from slow
control system
Cable #9, power to ALCT
Cable #13,
ANALOG+
power input
from DC-DC
Cable #14,
ANALOG power input
from DC-DC
Fig. 13. LVDB connections.
Cable #13,
DIGITAL+
power input
from DC-DC
Heatsink is insulated
from the board and
grounded on both ends.
Fig. 14. LVDB installed on chamber. Cover is removed to expose heatsink.
High-Voltage.
HV power supply has floating output, and the return wire is connected to the chamber
case, eliminating the ground loops. Chamber has 30 or 18 HV inputs, and the
multiconductor cable(s) #1 will be used to deliver the HV power to chamber. See the
document written by F. Catarsi and G. Passuello (CAEN) for complete set of HV
grounding recommendations [2].
References:
1. Endcap Muon Grounding Strategy. T. Y. Ling, C. J. Rush, Ohio State university.
1999.
2. General guidelines for HV grounding. F. Catarsi, G. Passuello, CAEN, 2000.
3. CMS EMU CSC cable list.