Low Voltage Service system for ATLAS Thin Gap Chamber

B.J. Ye(a,e) , O.Sasaki(b) , T.Takeshita(c) ,T. K.Ohska(d) ,T. Kobayashi(a)

(a)ICEPP, University of Tokyo, Japan
(b)Institute of Nuclear and Particle Physics, KEK, Japan
(c)Department of Physics, Shinshu University, Japan
(d)International Collaboration Office, KEK, Japan
(e)Department of Modern Physics, Univ. of Sci. and Tech. of China, P.R.China


Table of contents

1. Introduction

2. Outline of LV supply

2.1 Summary for ASD and PS-Pack electronics system
2.2 PS-Pack location
2.3 LV power consumption and current
2.4 LV supply scheme

3. LV bus

3.1 Doublet
3.2 Triplet
3.3 Summary for LV supply

4. The big wheel and LV stations

5.1 LV set location on the big wheel
5.2 Selection of copper materials


1. Introduction

This is a draft design of the Low Voltage (LV) service system for the front-end electronics of the Thin Gap Chamber (TGC) at June/2000. We discuss here the LV power supply for Patch-Panel and Slave Board (PS- Pack) as well as ASD Boards.
The ATLAS experiment in the LHC uses TGC as its forward muon trigger detectors. The TGCs are physically mounted on three big wheels, M1, M2 and M3 for each side. The M1 has three TGC layers, called as triplet. The other M2 and M3 have two TGC layers for each called as doublet. The Inner wheel is a doublet of TGC. The total number of TGCs is 3600. The total number of TGC signals from wires and strips is near 321k channels.
A PS-Pack serves 1/24th of triplet (M1) or two doublets (M2 and M3). A sub-PS-Pack consists of a mother Patch-Panel (PP) board, two daughter PP boards and two Slave Boards (SLB), which is called a standard sub-PS-Pack unit. A sub-LV unit of power distribution is a unit correspond to a sub-PS-Pack unit as shown in Fig.1. The power for the Amplifier-Shaper-Discriminator (ASD) Board is also supplied though cables in a 20-pair twisted-pair cable from the PS-Pack. Each ASD Board consists of 4 ASD chips. An ADS chip takes care of 16 wires/strips channels. Each sub-LV unit serves 16 ASD Boards up to 256 channels (one exception exists where a sub-LV unit in doublet serves 18 ASD Boards corresponding to 258 channels).

Fig.1 A sub-LV unit in the TGC sub PS-Pack system

The production of the ASD IC and 16-ch ASD Board has been finished. Each board contains four ASD ICs with the protection circuits and a test pulse circuit. The TGC-ASD chip characteristics are listed in Table 1. It shows the analog power consumption of each channel is 59 mW, 83% of which is drawn from 3V and 17% from -3V. The digital power consumption per channel is estimated about 30 mW, drawn from 3.3V in PPs and SLBs. Total power consumption is 89 mW per channel. The power distribution in each part is listed in Table 2. The total power is estimated about 45 kW.


Table 1 CXA3183Q TGC ASD chip characteristics

Sony Analog Master Slice (bipolar semi-custom)
Preamplifier gain of 0.8V/pC
16 nsec integration time
Input impedance of around 80W
Open-emitter analog outputs
Main-amplifier with a gain of 7
4 channels in a QFP 48 plastic package
Required voltage: -3V, GND
59 mW/ch when driving a 100W load
(+3V: 16.4mA, -3V: 3.25mA, 46mW in ASD chip and
13 mW at LVDS receive side)


The LV power supply scheme depends on the availability of the common ATLAS power supply scheme. In the present design, a 3 bus-line LV supply scheme is considered. Each LV-bus uses 4 wires for digital(+3.3V), analog(-3V) and a common ground. We will discuss this supply scheme in detail here.


Table 2 The power distribution in each electronic board
Board ASD-B PP SLB H-Pt ReadOut DCS TTC Contingency Total
Power 59 20 10 90 100 1 2
unit (mW/ch) (mW/ch) (W/crate) (W/crate) (kW) (kW) (kW) 10%
#of channels 321k 321k 321k 48 48
power 18.9kW 4.8kW 4.8kW 4.3kW 4.8kW 1kW 2kW 4.1kW 45kW


[1] ATLAS TGC Amplifier-Shaper-Discriminator ICs and ASD Boards, Oct.1, 1999.

2. Outline of LV supply
2.1 Summary for ASD and PS-Pack electronics system

The wheels M1, M2/M3 are divided into 24 identical elements, called sets. Each set is divided radially into two parts, namely the “Forward region” and the End-cap region”. There are 10 (triplet=M1) or 12 (doublet=M2/M3) TGC chambers in a set depending on the wheel. They are mounted to the support bars which composed of the part of the wheel.
The ASD Board is physically attached to the edge of a TGC and enclosed inside the TGC electrical shielding (Faraday cage). Signals from the ASD Boards are sent to a Patch-Panel (PP) board, which houses receivers from the ASD. Other components on a PP are TTC receivers and DCS, Bunch-Crossing Identification circuits, logic circuits to take care of physical overlap in the TGCs and fan-outs. Outputs from the PP board are sent to corresponding Slave Board (SLB) where the coincidence and read-out circuits are placed. For the M1 wheel, three groups of two ASD Boards are served by a SLB, which allows a 2-out-of-3 coincidence to be formed. For the M2/M3 wheels, four groups of two ASD Boards are served by a SLB and a 3-out-of-4 coincidence is made.
The PS-Pack, which consists of Patch Panels and Slave Boards, are placed on the accessible surfaces of the TGC wheels. Thus, PS-Packs for the M2 and M3 are mounted on the outer surface of the M3 wheel and those for the M1 are mounted on the inner surface of the M1 wheel. Figure 2 shows a very simplified ASD Board and PS-Pack electronics system.
Figure 2 : A sketch of ASD Board and PS-Pack electronics.
The total number of electronic channels in the TGC system is 321k. The details of the channel distribution over the four sub-wheels(EW: Endcap Wire, FW: Forward Wire, ES: Endcap Strip and FS: Forward Strip) are given in Table 3. The Table 4 gives the total number of channels, ASD Boards and SLBs for a set (1/24), octant, one side and both sides.


Table 3 The number of Channels, ASD chip, ASD Board, PP and SLB

_________________________________________________________________ *For Inner wheel, each TGC has a slave board, that is, it combines wires and strips in one SLB.
M2+M3 (1/48) one set(1/24)
Channel ASD chip ASD PP SLB Channel





EW 1214 306 78 5 10 2428 612 156 10 20
FW 506 128 32 2 4 506 128 32 2 4
ES 640 160 40 3 5 1280 320 80 6 10
FS 128 32 8 1 1 128 32 8 1 1
Total 2488 626 158 11 20 4342 1092 276 19 35
EW 606 153 42 4 7 1212 306 84 8 14
FW 335 84 21 2 4 335 84 21 2 4
ES 256 64 16 1 2 512 128 32 2 4
FS 64 16 4 1 1 64 16 4 1 1
Total 1261 317 83 8 14 2123 534 141 13 23
One set Octant
Board Channel ASD chip



PP SLB Channel ASD chip



EW 32 8 2 1 1/2 96 24 6 2 3/2
FW 64 16 4 1 1/2 192 48 12 2 3/2
ES 64 16 4 1 1/2 192 48 12 1 3/2
FS 64 16 4 1 1/2 192 48 12 1 3/2
Total 224 56 14 4 2 672 168 42 6 6


Table 4 The number of channel, ASD Board and SLB

One set Octant One side Two side



SLB Channel



SLB Channel



SLB Channel



M1 2123 141 23 6369 423 69 50952 3384 552 101904 6768 1104
M2+M3 4342 276 35 13026 828 105 104208 6624 840 208416 13248 1680
Inner 224 14 2 672 42 6 5376 336 48 10752 672 96
Total 6689 431 60 20067 1293 180 160536 10344 1440 321072 20688 2880


2.2 PS-Pack location

The PS-Packs for M2/M3 (doublet) are grouped in rows radially on the outer surface of the M3 wheel and those for triplet are grouped on the inner surface of M3 wheel. A sub-PS-Pack contains a mother PP board, two daughter PP boards and two SLBs. The number of channels for the SLBs and ASD Boards in each PS-Pack is listed in Table 4. There are 35 SLBs per set for the doublet and 23 SLBs per set for the triplet. In order to reduce physical size of a PS-Pack, a high-density connector (KEL, 8830E-080-170L) is employed at the inlet of the PP board. With this connector, the length of a sub-PS-Pack is not limited by the width of the connectors. Because the usable radial length on the outer surface of the M3 wheel is 6000 mm, we arrange the PS-Pack in two layer structure. It occupies 5000 mm in length including service PP board whose length is 525mm. As shown in Fig.3, all sub-PS-Packs are aligned in a straight line configuration so that other service systems such as LV supply and cooling system can be as simple as possible in its construction.

Figure 3 : A sketch of PS-Pack location and mounting place .
For the PS-Pack of the triplet (M1), it is a bit more complex than that of doublets because the support bar of the TGC chamber limits the available length on the inner surface of M1 wheel. The total usable radial length is 2500 mm but we need 3200 mm to arrange all sub-PS-Packs for M1 in one-line at this moment. We still designed all sub-PS-Pack units in one line which is based on the assumption that the support bar can be moved to the center of two TGCs by about 100 mm which can increase the usable length to 3200 mm.

2.3 LV power consumption
The total power-consumption depends on the number of front-end channels (wires or strips). The power is 89 mW per channel, which consists of 59 mW analog power for ASD Board and 30 mW digital power for PP and SLBs. 59 mW analog power is 83% from +3V and 17% from -3V. Table 5 lists the power and current distributions for both of end-cap and forward wires and strips for one set in detail. Total power needed is 386 W, 189 W and 20 W for doublet, triplet and inner PS-Packs, respectively. The total currents are 125A, 61A and 6.4A for doublet, triplet and inner PS-Packs, respectively ( They do not include the power for the service PP and TTC/DCS).
The LV power is assumed to be delivered by copper wires from the Power Service Station. The design of the LV power supply scheme depends on how much power is wasted by the cables. We use 4 wires for every LV-bus (1 wire for digital 3.3V, 2 wires for analogs +-3V and 1 wire for the common ground). For this scheme, the total currents for doublet, triplet and inner are shown in Table 6 for each wire, suppose one LV-bus-line is used for delivering power to each set .

Table 5 Power and current of end-cap and forward wires and strips for 1/24 unit.
(They don’t include power in service PP and TTC/DCS)

Current (A)

Digital 3.3V

Power (W)

Digital 3.3V

Current (A)

Analog +-3V

Power (W)

Analog +3V

Current (A)

Analog -3V

Current (A)

EW 72.84 22.07 143.25 39.82 7.89
FW 15.18 4.6 29.85 8.3 1.64
ES 38.4 11.64 75.5 20.99 4.16
FS 3.84 1.16 7.55 2.1 0.42
Total 130.26 39.47 256.18 71.21 14.11
EW 36.36 11.02 71.51 19.88 3.96
FW 10.05 3.05 19.76 5.49 1.1
ES 15.36 4.65 30.21 8.4 1.67
FS 1.92 0.58 3.78 1.05 0.21
Total 63.69 19.31 125.26 34.82 6.94
EW 0.96 0.29 1.89 0.52 0.1
FW 1.92 0.58 3.78 1.05 0.21
ES 1.92 0.58 3.78 1.05 0.21
FS 1.92 0.58 3.78 1.05 0.21
Total 6.72 2.04 13.22 3.67 0.73
200.67 60.81 394.65 109.7 21.78


Table 6 Total current values of 3 voltages and common ground for doublet, triplet and inner.
(Digital currents do include those for the service PP and TTC)
Doublet Triplet Inner
Analog +3V 71.2A 34.7A 11.0A
Analog -3V 14.1A 6.9A 2.2A
Digital +3.3V 48.6A 25.9A 6.9A
Common ground 105.7A 53.9A 15.7A


2.4 LV supply scheme

LV supply scheme was designed to use 4-wires, that is, analog +3V, analog -3V, digital 3.3V and a common ground as shown in Fig.4.

Figure 4: Four wire LV-supply scheme.

Analog and digital power wires are isolated with the adjacent LV supply unit, after the fan out of the LV Power supply. Each analog power wire is isolated so that the different ASD LV power supply can not influence with each other as shown in Fig.5. In this case, the current in common ground should be the sum of the total currents for analog ground and digital ground.

Figure 5 : Four wire LV-supply sustem in detail.

3. LV-bus

As shown above, the current value in each wire is very large, when one LV-bus is used to deliver power as shown in Table 6. The cross section of the copper wires also will be large in order to reduce power dissipation in the wire, for example, it needs 170 mm2 cross section of copper for common ground for doublet. It is not so convenient for repairing or checking electronic parts, in case of the such huge power wires. Based on these considerations, we plan to use 3 LV-buses to deliver LV power for each set. Two LV-buses are used for end-cap wires and strips (each one for 1/24 wheel, one LV-bus including service PP and TTC). Another LV-bus is for forward wires and strips as shown in Fig.6.

Figure 6 : LV-bus system and their locations
We consider about 10% power is dissipated in the LV-bus as the acceptable requirement for determining the cross section of copper wire. We refer to the standard of American Wire Gauge (AWG) for the cable size as shown in Table 7.

Table 7 Value of cross sections for different type of wires
Type Cross-section Type Cross-section Type Cross-section
(mm2) (mm2) (mm2)
AWG6/0 170.5 AWG3 26.67 AWG11 4.17
AWG5/0 135.2 AWG4 21.15 AWG12 3.31
AWG4/0 107.2 AWG5 16.77 AWG13 2.63
AWG3/0 85.04 AWG6 13.3 AWG14 2.08
AWG2/0 67.43 AWG7 10.55 AWG15 1.65
AWG0 53.49 AWG8 8.37 AWG16 1.31
AWG1 42.41 AWG9 6.63 AWG17 1.04
AWG2 33.63 AWG10 5.26 AWG18 0


The names of LV-bus and sub-LV unit are presented as Table 8. We use A, B and C to indicate the 3 LV-buses groups. For example, LV-D05A means this LV-bus is for No.05 set doublet PS-Pack and A-group LV-bus. LV-D05A03 means No.03 sub-LV unit on No.05 set doublet PS-Pack and A-group LV-bus.


Table 8 : LV-bus and sub-LV unit naming

LV-bus D/T number A/B/C number

D: doublet

T: triplet

Set number

From 00 to 23

Bus name

A: endcap including SPP and TTC

B: another endcap group

C: forward

Only for sub LV unit


3.1 Doublet

The length of the wire is an important factor to select the copper wire. This depends on the location of PS-Pack in the big wheel. In this chapter, we consider a fixed wire length of 15m between LV service station and PS-Pack (edge of the wheel) for a simplicity. Since the length of PS-Pack is 5m for the doublet, the total length of LV-bus wires is now 20m.
The LV-D00A serves for both end-cap wires and strips for 1/48 wheel including service PP and TTC. The power in service PP is estimated to be about 7W. The power for TTC is about 23W in doublet. The power for DCS is delivered by a special cable because it uses a 5V. The LV-D00B serves the end-cap wires and strips for another 1/48 wheel. The LV-D00C is only for the forward wires and strips as shown in Fig.7.

Figure 7: LV-distribution scheme for the doublet.

There are total 20 sub-LV units in a doublet (9 for LV-D00A, 8 for LV-D00B and 3 for LV-D00C, respectively). The length of each sub-LV unit is about 0.5m. The current on LV-bus wires were indicated by Ii (i=1 to 8 for LV-D00A, 1 to 7 for LV-D00B and 1 to 2 for LV-D00C) as shown in Fig.7.

Figure 7 : LV-distribution scheme for the doublet in detail.

After fanned out to each sub-LV unit, the current on LV-bus wire is decreased along PS-Pack. The LV delivered from the common LV-bus to each sub-LV unit by a short cable. The power supply and currents for each sub-LV unit are shown in Table 9. The current distributions in LV-buses are calculated and shown in Table 9.

Table 9:Currents in LV buses
For this LV supply scheme, the analog and the digital power lines share a common ground line. They are distributed with four kinds of copper wire, as shown in Fig.8.

Table 10:Currents in LV buses for the triplet.

Figure 8 : LV-distribution scheme for the doublet.

The values of supply voltages in LV station should be a little larger than that in the PS-Pack which is summarized in Table10, because of the voltage drop along with wires.

The figure 8 shows the electric potential drop along the wires and voltages supplied in LV service station for 3 LV-buses.

The power dissipations in the cable are 11.4%, 10.5% and 10.2% for LV-D00A, LV-D00B and LV-D00C in average, respectively. Average power loss for one set is about 10.9% for doublet. Total copper material weight is 82.5kg for one set and 3961kg for both sides for the doublet.

3.2 Triplet

The length of triplet PS-Pack is 3 m and sub-LV unit is 0.5 m as shown in Fig.9.

Figure 9: The LV supply scheme for the triplet PS-Pack .

The distance between LV service station and the PS-Pack (edge-end of service PP) is supposed to be 15m. The total length of the LV-bus is 18m. There are total of 14 sub-LV units (6 for LV-T00A, 5 for LV-T00B and 3 for LV-T00C, respectively). The power and current for each unit is listed in the Table 11.

Table 11 : Porperties of the copper wires fot the triplet.

For the LV-T00A, it serves the end-cap wires and strips as well as the services PP and TTC. Power in service PP is estimated to be 5W and in TTC to be 17W. Both are a little bit smaller than that of the doublet due to smaller numbers of the sub-LV units. Table 11 shows detailed powers and currents in each sub-LV unit for 3 LV-buses. The currents in LV-bus are gradually decreased along with the PS-Pack after fanning out to sub-LV unit. The power dissipation of 10 % in wire is assumed to determine the cross section of wire. The results are listed in Table 12.

Table 12 : Porperties of the copper wires fot the doublet.

For the digital and +3V analog wire in LV-T00A, the same wire size is chosen due to the similar power consumption. For the LV-T00B and LV-T00C, the wire with same size is selected for both analog +3V and ground wire. The rates of actual power loss to the power delivered in the wire is about 11.2W/109.1W (=10.3%), 9.45W/85.1W (=11.1%) and 4.1W/39.3W (= 10.4%) for LV-T00A, LV-T00B and LV-T00C, respectively. Actual total power loss in wires is about 24.7W for delivering 233.4W power for one set PS-Pack. The electric potential is dropped along LV-bus due to wire resistance. Actual voltages supplied from LV service station should higher than the required values of voltages in PS-Pack as shown in Fig.10.

Figure 10: The copper wire type and its electric potential drop in the LV-wires .

This has been calculated to be 10-11% higher than 3.3V and Ī3V. The copper materials weight is about 33.5kg and 1606.4kg for one set and both sides of big wheels for the triplet.
re 12: The copper wire type and its electric potential drop in the wires.

3.3 Summary of the LV supply

For the proposed scheme described here with 4-wires and 3 LV-buses supply scheme, both doublet and triplet need 12 wires for one set and 576 wires for both sides of the big wheel. Total sub-LV unit in the triplet is 288, 240 and 144 for bus-A, bus-B and bus-C, respectively. Total sub-LV unit in the doublet is 432, 384 and 144 for bus-A, bus-B and bus-C, respectively. Based on the assumption that 24 LV-bus can be housed in a crate and 3 crates in a rack. The whole TGC LV supplied system needs 12 crates and 4 racks as shown in Table 13. Both triplet and doublet need 1 rack for its power supply at each side of the big wheel. We suggest that each side uses two racks, one is located on ground and another is located in a position of 22m high above ground. This can reduce the length of wires. Each rack serves half wheel for both the doublet and the triplet. For triplet the power is below 3 kW/crate and blow 6 kW/rack, and for doublet 6kW/crate and 12kW/rack The total LV power delivered is 33.3kW for ASD and PS-Pack ( It doesn’t include power in DCS, which is about 1kW in total). Total power loss in LV-bus wires is about 3.6kW.

Table 13: LV power supply modules and maximum power per module for triplet and double

One side Two sides Max.power per module Actual
Modules Bus-A Bus-B Bus-C Bus-A Bus-B Bus-C Bus-A Bus-B Bus-C power
Channels 20688 20688 9576 41376 41376 19152 89mW 89mW 89mW
Sub-LV unit 144 120 72 288 240 144 24W 8.4W 6.4W
Triplet LV-bus 24 24 24 48 48 48 109W 85W 40W
Crate 1 1 1 2 2 2 2.6kW 2.1kW 0.96kW
Rack 1 2 5.7kW 11.2kW
Channels 44496 44496 15216 88992 88992 30432 89mW 89mW 89mW
Sub-LV unit 216 192 72 432 384 144 33W 8.6W 8.6W
Doublet LV-bus 24 24 24 48 48 48 216W 183W 63W
Crate 1 1 1 2 2 2 5.2kW 4.4kW 1.5kW
Rack 1 2 11.1kW 22.1kW
Channels 65184 65184 24792 130368 130368 49584
Sub-LV unit 360 312 144 720 624 288
Total LV-bus 48 48 48 96 96 96
Crate 2 2 2 4 4 4
Rack 2 4 33.3kW

4. LV station on the big wheel

4.1 LV power supply's location on big wheel
Locations of PS-Pack on the big wheel are shown in Fig.11 for the doublet.

Figure 11: Locations of the PS-Packs on the big wheel .

The LV power supply racks locate at between M1 and M3 and at close to the hall USA15 as shown in Fig.12.

Figure 12:Top view of the TGC wheel and its service system .

For Inner wheel, the LV power is supplied by another LV rack. We suppose that the distance from LV rack to M1 or M3 wheel is same to be 1 m. Two racks are required for LV supply. One rack is on the ground and another is fixed at a high position about 22 m above ground. An additional cable of about 2m is required for both M1 and M3 wheels in order to move the wheel expediently.

4.2 Selection of copper materials

We suppose each LV rack to service the half PS-Pack on the big wheel. The LV cable for each PS-Pack set is first to route to the point which is on the edge of the wheel and has a minimum length to LV rack. We call the position as LVP. The length of LV-bus wire for each PS-Pack set is different and it depends on its location. The lengthes of cables for different PS-Pack locations are calculated as following:

dL = dL0 + dL1 + dL2 + dLadditional

where dL0 is the length of LV-bus in PS-Pack, which for doublet are 4.5m, 4m and 5m for Bus-A, bus-B and bus-C, for triplet all bus is 3.2m. The dL1 is the length between LV rack and LVP, which is supposed to be 1 m. The dL2 is the length between each PS-Pack set and LVP, which is very largely different for different PS-pack set. DLadditional is 2m which is the same additional cable for both M1 and M3 wheels.
We suppose the 10% power dissipation in cable as a basic condition. Table 14 and 15 give the common wire length (row # 3), actual cross section values(AWG standard, row # 4-7), supply voltage values in LV station due to electric potential drop in cables (row # from 8 to 11 ) and actual power dissipations in cable(row # from 12 to 16) for each set for the triplet and the doublet. The average length of wires is 15.3m for the triplet PS-Pack and is 17.2m for the doublet PS-Pack. According to the result, the values of cross section are selected depending on the length of cable by keeping the power dissipation in cable to be about 10%. In order to simplify the cable used, some researchers suggest to use only one size of wire. But it is very difficult to meet the requirement for each set because the current-values are quite different.
Table 16 is the results for copper materials budget and cost. It shows that copper materials budget for the doublet is about 3 times expensive than that for the triplet. Besides, the length of additional cable for M3 wheel is very important for decreasing the copper materials budget.

Table 14 : Summary for copper materials budget and cost

Copper materials* [kg] Copper materials* [kg] Cost*[kCHF]
One wheel Two wheels Two wheels
Triplet 256 198 116 570 513 395 233 1141 21.2
Doublet 664 671 240 1575 1328 1341 483 3152 58.6
Total 920 869 356 2145 1841 1736 716 4293 79.8

* It didn’t include the weight of shielding materials for cable.
** CERN cost: 18.6CHF per kg copper cable.

Table 15 : Length and cross-section of the wires fot LV-sysytem (LV-A).

Table 16 : Length and cross-sections of the wires for LV-system (LV-B and -C).