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New approach to CPC design 9 December 2002 A.P.Kashchuk (LNF/INFN), Frascati) 1 It is my 1-st presentation from LNF/INFN (Frascati) The scientific work is still under development and the new ideas have to be tested… Triggered by P.Campana Why results on cross-talks obtained with small chamber in May 02 are somehow better than with the large M0 prototype tested in October 02? 9 December 2002 A.P.Kashchuk (LNF/INFN), Frascati) 2 I’d like to add: ? ? 2 problems observed in beamtests have to be explained and suppressed: - rather high cross-talks from wires to pads; - double and multiple TDC spectra Problems mentioned here were observed already in M2R1 and other prototypes built at CERN, as well as in Ferrara’s prototypes; 50% crosstalks observed in some conditions in M3R3 in October 2002 beam-tests at operational HV 9 December 2002 A.P.Kashchuk (LNF/INFN), Frascati) 3 Cross-talks 9 December 2002 ? A.P.Kashchuk (LNF/INFN), Frascati) 4 Cross-talks along the wires (longitudal) perpendicular to wires (transverse) Longitudal crosstalks are less studied and much less suppressed 9 December 2002 A.P.Kashchuk (LNF/INFN), Frascati) 5 According to specification (LHCb 2000-061, W.Riegler) Cross-capacitance Cwp will be increased with pad size, as shown: M1 M2 R3 M3 M4 M5 LNF M0 Pad size (cm) & Number of pads Cdet (pF) Cwp (pF) CPC: 2,5 (48x4) CPC: 2.5,12.5 (24x2) CPC: 2.7,13.5 (48x2) CPC 5.8x14.5 (24x2) CPC: 6.2x15.5 (24x2) 30.3 4.75 50 15 56 21.5 90 40 140 46 Cwp=0.475hw (pF) where h, w are pad height and width (cm) 9 December 2002 A.P.Kashchuk (LNF/INFN), Frascati) 6 Let’s measure: (very good agreement with table shown above) Cwp=20.5pF (small chamber) Charge on pad (fC) Cwp measured in large M3R3 is absolutely similar 60000 40000 20000 0 y = 20,493x - 446,41 0 500 1000 1500 2000 2500 Eq.Volt.Step on strip (mV) 9 December 2002 A.P.Kashchuk (LNF/INFN), Frascati) 7 The original idea was following: Cross-talks from wire strips to pads (longitudal) will be reduced with grounding wire strips through HV-capacitors 9 December 2002 A.P.Kashchuk (LNF/INFN), Frascati) 8 RC-model (Rwire =90 Ohm/m) Only capacitive coupling is taken into account in this model Wire strip with 4 wires Signal from particle Assumed that width of wire strip is equal to cathode pad Cathode pad current source HV-capacitor grounded on one side, as shown 9 December 2002 A.P.Kashchuk (LNF/INFN), Frascati) 9 Wire strip as a transmission line, i.e. LC-model (first proposed by LNF group) Cathode pad current source Each wire can be considered as a transmission line Wires in strip are connected in parallel: L reduced, C increased (product LC is the same) 9 December 2002 A.P.Kashchuk (LNF/INFN), Frascati) 10 Recently it has been found: the wire strip is ringing (response of wire strip in small LNF prototype made with injector) HV-capacitor 680pF directly grounded f=95 MHz The ringing frequency depends on inductance in series to HV-capacitor (what the reason?) f=60 MHz 9 December 2002 A.P.Kashchuk (LNF/INFN), Frascati) 11 Cross-talk profile from wires to cathode pads in the large M3R3 prototype Volt. step on strip (strip is floating) 20ns/div Pad-1 (15%) Central Pad Ratio 2-nd/1-st peak 20% Ringing 18 ns Pad+1 (20%) 9 December 2002 A.P.Kashchuk (LNF/INFN), Frascati) 12 Fine waveform structure at voltage rise time 1.5ns: One can see 4 ns oscillation High frequency is due to LC of the transmision line itself 9 December 2002 A.P.Kashchuk (LNF/INFN), Frascati) 13 Response of wire strip in small LNF prototype made with Current Injector Ringing 13ns Strip is grounded through 680pF, with adding inductance period is increased 9 December 2002 A.P.Kashchuk (LNF/INFN), Frascati) 14 Equivalent circuit 1.Inductance blocks HV-capacitor effect Wire strip Terminated end Cathode pad High cross-talk: Cwp Q pad Qstrip Cstrip Compare to ideal case: Cwp Q pad Qstrip CHV 2.Another parasite effect f ringing 9 December 2002 1 2 Ltrace Cequivalent Assumed Cstrip C HV But!!! Cwp C pad C HV Cequivalent Cstrip A.P.Kashchuk (LNF/INFN), Frascati) 15 What LC-model shows? with HV-capacitors grounded at inductance 3nH in series (perhaps, can be acheaved) 1-side strip termination with 0 Ohm 1.0uA 2-side (peak less factor 2) 1.0uA 0.5uA 0A 0A -0.5uA -1.0uA 0s 10ns 20ns 30ns I(R7) Time Peak=1uA Ringing= 8ns 9 December 2002 40ns 50ns -1.0uA 0s 10ns 20ns 30ns 40ns 50ns I(R7) Time Peak=0.5uA Ringing= 3ns A.P.Kashchuk (LNF/INFN), Frascati) 16 Stray inductance (printed traces) in series to HV-capacitors and full capacitance of the wire strip mainly specify the ringing frequency Green – 3nH Red – 300nH (can be if width of traces 0.25mm, see M3R3) 1-side strip termination with 0 Ohm 2-side termination 2.0uA 2.0uA 0A 0A -2.0uA 0s 20ns 40ns 60ns I(R7) Time Green peak=1uA Red peak=1uA Ringing=30ns 9 December 2002 80ns 100ns -2.0uA 0s 20ns 40ns 60ns 80ns 100ns I(R7) Time Green peak=0.5uA Red peak=1uA Ringing=20ns A.P.Kashchuk (LNF/INFN), Frascati) 17 Correct strip termination with 377 Ohm can not be used 1.0uA 1- signal at far end to capacitor R0 377 Ohm 0A -1.0uA -2.0uA 0s 10ns 20ns 30ns 40ns 50ns I(R7) Time 1.0uA 0A 2- middle -1.0uA -2.0uA 0s 10ns 20ns 30ns 40ns 50ns 30ns 40ns 50ns I(R7) Time 1.0uA 0A -1.0uA 3- near end 2-side termination through 680pF At 1-side termination amplitude will depend on signal position along the strip (see next slides) -2.0uA 0s 10ns 20ns I(R7) Time No ringing, waveforms are independed to position of the signal source, but the highest crosstalks will be in this case 9 December 2002 A.P.Kashchuk (LNF/INFN), Frascati) 18 Inductance in series to HV-capacitors (1-side termination with 680pF and 50 Ohm) Same schematics No ringing , but not enough cross-talk attenuation Peak independ on Lstray due to 50 Ohm 3 2 1 2.0uA 1.0uA 2.0uA 2.0uA 1.0uA 1.0uA 0A 0A 0A -1.0uA 0s 10ns 20ns 30ns I(R7) Time 40ns 50ns -1.0uA 0s 10ns 20ns 30ns 40ns -1.0uA 0s 50ns Time Green=3nH Red=100nH 9 December 2002 10ns 20ns 30ns 40ns 50ns I(R7) I(R7) Time Scale +/-2uA 10ns/div A.P.Kashchuk (LNF/INFN), Frascati) 19 Inductance in series to HV-capacitors (1-side termination with 680pF and 0 Ohm) Same schematics Better attenuation, but ringing at R=0 1 2 3 2.0uA 2.0uA 2.0uA 0A 0A 0A -2.0uA 0s 10ns 20ns 30ns 40ns -2.0uA 0s 50ns 10ns 20ns 30ns I(R7) I(R7) Time 40ns -2.0uA 50ns 0s Time Green=2nH/Ringing 200MHz Red=100nH/Ringing 70MHz 9 December 2002 A.P.Kashchuk (LNF/INFN), Frascati) 10ns 20ns 30ns 40ns 50ns I(R7) Time Scale +/-2uA 10ns/div 20 Inductance in series to HV-capacitors (2-side termination with 680pF and 20 Ohm) Same schematics Good cross-talk attenuation factor at 20 Ohm High inductance leads to ringing even at R=20 Ohm and drastically reduces cross-talk attenuation 3 2 1 2.0uA 0A 2.0uA 2.0uA 0A 0A -2.0uA -2.0uA -2.0uA 0s 10ns 20ns 30ns I(R7) 40ns 50ns 0s 10ns 20ns 30ns 40ns 50ns I(R7) Time 0s 10ns 20ns 30ns 40ns 50ns I(R7) Time Time Red=100nH/Ringing 100MHz Green=3nH/No ringing 9 December 2002 A.P.Kashchuk (LNF/INFN), Frascati) Scale +/-2uA 10ns/div 21 Inductance of printed trace (example): h L 4 10 l w 7 if w=0.25mm trace width (in M3R3 prototype) h=1.5mm pcb thickness l=3-10cm length of trace (in M3R3 prototype) then L=100-1000nH Tringing 20 60ns @ C=100pF if w=1.2cm then L=5nH can be achieved 9 December 2002 A.P.Kashchuk (LNF/INFN), Frascati) 22 Ringing on wire strip can double/multiple signals and TDC spectra Threshold defined experimentally: for wire readout –7fC for cathode (single) – 5fC FEE noise 50e/pF is not the first reason for threshold choice, mainly cross-talks define threshold, at efficiency 95%/gap Dynamic range of signals in CPC is large (100) Average signal 50fC So, high probability for after-pulsing can be found at bad wire strip termination and imperfect layout in CPC at any frequency of ringing (it depends on design) 9 December 2002 A.P.Kashchuk (LNF/INFN), Frascati) 23 If Cstrip=Cwire is high? 2.0uA 0A +/-2uA -2.0uA 0s 20ns 40ns 60ns 80ns 100ns 80ns 100ns I(R7) Time 200nA Excellent result 0A +/-0.2uA -200nA -400nA 0s 20ns 40ns 60ns I(R7) Time No ringing and high cross-talk attenuation 9 December 2002 A.P.Kashchuk (LNF/INFN), Frascati) 24 Conclusion ! CPC design can be improved following the way: No ringing must be on the wire strips at perfect design 1.No wire segmentation is needed in CPC design one of the effective way No HV-capacitors and resistorrs (cheaper and much easy design), wires are connected to one HV-resistor. Minimisation of the trace inductances has to be done in the Combined readout chambers, which dumps effect of low impedance. 2.Double Cathode Readout scheme, perhaps, can be used in some cases below M3R3 also effective way at large Cwires (it allows increase threshold at fixed HV) already tested in M1R1 with excelent results (because very low Cwp and good attenuation of the cross-talks from wires) 9 December 2002 A.P.Kashchuk (LNF/INFN), Frascati) 25 Summary Voltage zero must be on the wire strips at perfect CPC design, i.e. M1 M2 M3 Cwire M4 M5 CPC 5.8x14.5 (24x2) CPC: 6.2x15.5 (24x2) LNF M0 R3 Pad size (cm) & Number of pads CPC: 2,5 (48x4) CPC: 2.5,12.5 (24x2) Double Cathode readout (CRO) below M3R3. No wire segmentation Cdet (pF) Cwp (pF) 9 December 2002 30.3 4.75 50 15 CPC: 2.7,13.5 (48x2) ? 56 21.5 A.P.Kashchuk (LNF/INFN), Frascati) Single CRO. No wire segmentation 90 40 140 46 26