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Cables (/connectors) Signal inventory signal types / characteristics extra signals of pile-up Types of cables twisted pair vs. striplines Cable test Other (open) issues grounding & shielding buffering on flange vacuum Scta beetle air Optional buffer unshielded 1 .. 2 meter Receiver in racks shielded 10 .. 15 meter Signal inventory Low voltage power lines Analog outputs Digital control (lvds / cmos) Digital outputs (lvds, pile-up only) Other signals detector bias temperature sensors Low voltage power Simple calculation: 1/2 wheel = 16 frontend chips 16 * 500 mW = 8 Watts If Vdd = 2.5 volts => I= 3.2 Amp Copper area needed > 1 mm2 cooling? 1 meter = 170 mW Analog output signals Balanced output pair few hundred millivolts for 10 Mip signal Bandwidth >> 40 MHz sensitive to pickup 4 pairs per frontend chip Digital control lines LVDS (low voltage differential signalling) clock, trigger, reset frequency: 40 MHz line termination needed clock / trigger per 4 / 8 / (16) chips CMOS-level I2C interface low frequency line termination optional (series termination) one set of signals for 1/2 wheel? LVDS Driver: Receiver: 250 mV into 100 ohms 100 mV differential Maximum cable attenuation = 8 dB (Z0 = 100 ohms) Digital outputs Pile-up comparator outputs LVDS @ 80 Mbit 16 pairs per frontend chip, 256 for 1/2 wheel extra connectors on hybrid needed Other signals Bias for detector high voltage, upto 500 Volts ? low current Temperature sensors specification depends on sensor type no-high speed, low current… 1 sensor for 1/2 wheel Summary signal type # signal pairs cable type power 4? power analog 64 twisted pair digital control 12 (6)+ 2 or twisted pair digital output 256 twisted pair other twisted pair ? 2 Cable requirements vacuum compatible radiation hard moderate signal loss flexible thin characteristic impedance of 100 ohms polyimide (kapton) isolation Cable “specifications” Cable impedance geometry dielectric constant of isolation (~ 3) Loss DC resisitive loss losses due to skin effect, proximity effect dielectric loss Dispersion Cable losses Wire resistance Skin depth Dielectric loss dispersion Rdc Scu l A 66m f ( MHz) ~1.7 per meter for 0.01 mm2 ~10 m @ 40 MHz low for good dielectrics Example Diameter 0.1 mm Rdc = 1.3 / m skin loss @ 40 Mhz adds a factor 2.5 ~20% signal loss for 2 meter same copper area for stripline (35 m Cu) width = 0.225 mm skin loss @ 40 Mhz adds a factor 1.5 ~13 % signal loss for 2 meter Impedance of cable d Twisted pair 120 D Z0 arccos h( ) r d D For kapton Z0 ~ 100 ohms if D = 2*d Microstrip line w s w See figure h Grounding /shielding Questions Central (star) ground, where shielded cables upto flange vacuum cables run close to machine ground Buffering Rad-hard components cooling problem
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