position, charge and time measurements with after+ eric delagnes
DESCRIPTION
Position, Charge and Time measurements with AFTER+ Eric Delagnes. Q. AFTER +: The Analog Side. Required for spark protection. Q/C f. Pole-zero + Shaper. 2 nd stage + SCA. Digitization + digital treatment. Cc. CSA. 1 zéro (Z 1 =P 1 ) CR-(RC) 2 filter BandPass filter - PowerPoint PPT PresentationTRANSCRIPT
1XY,Q,T measurements with AFTER+ Bordeaux June 17th
2008
Position, Charge and Time Position, Charge and Time measurements with AFTER+measurements with AFTER+
Eric DelagnesEric Delagnes
2XY,Q,T measurements with AFTER+ Bordeaux June 17th
2008
AFTER +: The Analog SideAFTER +: The Analog Side
CSAPole-zero+ Shaper
2nd
stage + SCA
Integrator+ Low Passpole P1
1 zéro (Z1=P1) CR-(RC)2 filterBandPass filter(1 zero @ origin +3 programmable poles)
Cc
Required for spark protection
Sampling @ programmablefrequency (beware of the Nyquist criterium for signal & noise to avoid aliasing)
Q
Q/Cf
Noise1/f
white
40dB/dec
10dB/dec
20dB/dec2ND STAGE & SCA noise
Digitization+ digital treatment
3XY,Q,T measurements with AFTER+ Bordeaux June 17th
2008
AFTER +: The timing Side (1)AFTER +: The timing Side (1)
AFTERQ
TriggerSynchroniser +
Processor +STOP timing
AFTERQ
Trig AFTER i CK
Trig AFTER 0
STOP
Ext Trig (opt)
•Everything is synchronous with the Everything is synchronous with the samesame CK (T CK (TCKCK period) period)
(not exactly the case with T2K FEM 10ns incertitude)(not exactly the case with T2K FEM 10ns incertitude)•Timing offsets between boards supposed to be stable and calibratedTiming offsets between boards supposed to be stable and calibrated
=> calibration system required to achieve fine timing.=> calibration system required to achieve fine timing.•STOP = Trigger + NPOST x TSTOP = Trigger + NPOST x TCKCK = signal synchronizing everything = signal synchronizing everything
Time calibrator
4XY,Q,T measurements with AFTER+ Bordeaux June 17th
2008
AFTER +: The timing Side (2)AFTER +: The timing Side (2)
•NNstopstop = N = N last written celllast written cell
•In AFTER+ the readout can start NIn AFTER+ the readout can start NReadoff Readoff cells after the last written cell => If cells after the last written cell => If
NNjj is the index of the cell during the readout is the index of the cell during the readout (1= first cell read)(1= first cell read)•(Nstop –Ni) mod 511 = 511 - (NReadoff +Nj)(Nstop –Ni) mod 511 = 511 - (NReadoff +Nj)
•If we implement time zero-suppress option in AFTER+:If we implement time zero-suppress option in AFTER+:•different time readout window can be read for different AFTER chips.different time readout window can be read for different AFTER chips.
•The readout index NThe readout index Njj is not sufficient to calculate the time. is not sufficient to calculate the time.
•Each chip must provide an extra information Noffsetm.Each chip must provide an extra information Noffsetm.
•Each SCA sample Each SCA sample NiNi can be « absolutely » timed with the ck can be « absolutely » timed with the ck precision:precision:
ttii = t = tstopstop – ( – (NNstopstop –N –Nii) mod 511 x T) mod 511 x TCKCK
must be known
from trigger processor
Precision can be far better than TCK
limited by uncalibrated skew and jitters
NReadoff
STOP
Noffsetm
Noffsetn
AFTER+# m
AFTER+# n
5XY,Q,T measurements with AFTER+ Bordeaux June 17th
2008
The signal for TPC with a Micromegas The signal for TPC with a Micromegas endplateendplate
•Elementary Current signal from a primary electron collected on a TPC pad.Elementary Current signal from a primary electron collected on a TPC pad.•Widened byWidened by::
•longitudinal diffusion for large Z.longitudinal diffusion for large Z.•geometry for tracks with non 0 angles.geometry for tracks with non 0 angles.
• In all cases: sum of elementary signals with eventually different time offsetsIn all cases: sum of elementary signals with eventually different time offsets •Rectangular shape is a reasonable approximation for simulations.Rectangular shape is a reasonable approximation for simulations.
0,07
0,00
0,01
0,02
0,03
0,04
0,05
0,06
Time17575 80 90 100 110 120 130 140 150 160
fast e- signal
~10% of Q ion signal~90% of Q.25-100ns duration depending of amplification gap
6XY,Q,T measurements with AFTER+ Bordeaux June 17th
2008
XY position determinationXY position determination•@ first order: given by the position of the pad with maximum of charge.@ first order: given by the position of the pad with maximum of charge.
=> resolution s0~ pad size/√12=> resolution s0~ pad size/√12•Centroïd calculation may help. But the lateral diffusion is very small for Centroïd calculation may help. But the lateral diffusion is very small for small Z for standard Micromegas (diffusion is typ small Z for standard Micromegas (diffusion is typ ~ 15µm)~ 15µm)
Colas et al., simulations/exp. for ILC TPC.
limited resolution for small Z. For higher Z, diffusion helps.Very large improvements for resistive anodes.
•Weights for centroïd calculation = Q (see next slides) •Centroïd calculations are only effective is S/N is very good.•Crosstalks and transfer function spread deteriorates resolution.
7XY,Q,T measurements with AFTER+ Bordeaux June 17th
2008
Crosstalk et alCrosstalk et al
•Crosstalk in the modern FE can be very small. Typically ~0.3% for AFTER. It is mainly derivative.•The main crosstalk comes from the FE to detector coupling
DAC
AC
F
Dout CC
C
C
QV
~
Gain depend on CD and CAC
Crosstalk (non derivative)
).2(~
ACP
P
F
Dout CC
C
C
QV
(Xtalk effect neglect)
CAC must be large compared to CD and CP
8XY,Q,T measurements with AFTER+ Bordeaux June 17th
2008
Charge measurement (cont)Charge measurement (cont)• QQtottot = SUM( Q = SUM( Qii))
Ballistic deficit illustrated: (100ns CR-RC4 shaper)
1,2
0,0
0,1
0,2
0,3
0,4
0,5
0,6
0,7
0,8
0,9
1,0
1,1
Signal duration/ Filter Peaking time8,00,1 0,5 1,0 1,5 2,0 2,5 3,0 3,5 4,0 4,5 5,0 5,5 6,0 6,5 7,0 7,5
amp_vs_tp
• For accurate charge measurement shaping time >> signal durationFor accurate charge measurement shaping time >> signal duration• If signal duration is constantIf signal duration is constant => Ballistic deficit is constant => just a small => Ballistic deficit is constant => just a small decrease of S/N.decrease of S/N.•If not ( tracks with angle, large Z)=> dependancy of transfer function with If not ( tracks with angle, large Z)=> dependancy of transfer function with signal duration => degradation of Q resolution.signal duration => degradation of Q resolution.
9XY,Q,T measurements with AFTER+ Bordeaux June 17th
2008
• Samples SSamples Sii can be combined can be combined• FIR filter for example: FIR filter for example:
•aa00 =1, a =1, aii=0 => peak measure.=0 => peak measure.•aaii =1 (0<=i<=w) => gated integrator. =1 (0<=i<=w) => gated integrator. •optimal filter (calculated from signal shape +noise spectrum). optimal filter (calculated from signal shape +noise spectrum). W. Cleland, NIM A 338 (1994)
•Other techniques may be used (fit, correlation…) allowing also to extract Other techniques may be used (fit, correlation…) allowing also to extract timing timing ((P. Bertin et al. DVCS/E00-110 experiment : Final Readiness Report).
What can be done : What can be done : Reduce the effect of the asynchron beahvior of the pulse.Reduce the effect of the asynchron beahvior of the pulse.ENC improvement.ENC improvement.ballistic deficit removing. ballistic deficit removing.
Taking advantage of sampling for charge Taking advantage of sampling for charge measurement.measurement.
ii SaQ ~ change the effective filter
10XY,Q,T measurements with AFTER+ Bordeaux June 17th
2008
Effect of asynchronism Pulse/sampling Ck.Effect of asynchronism Pulse/sampling Ck.
11XY,Q,T measurements with AFTER+ Bordeaux June 17th
2008
Improving Equivalent noise charge by Improving Equivalent noise charge by filtering ?filtering ?
•No magic improvement to expect:No magic improvement to expect:•CR-RC(n) filter noise performances are typ. 10% worst than optimal CR-RC(n) filter noise performances are typ. 10% worst than optimal one.one.•What can only be done => change the effective filter peaking time.What can only be done => change the effective filter peaking time.•The optimum will depend on the noise spectral density The optimum will depend on the noise spectral density
•limited by 1/f and 2limited by 1/f and 2ndnd stage noise. stage noise.•Be careful to aliased second stage noise.Be careful to aliased second stage noise.
Range:120fC
400
450
500
550
600
650
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750
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850
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950
1000
1050
100 200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400 1500 1600 1700 1800 1900 2000
Peaking Time (ns)
NO
ISE
(e
-)
ASIC(Cin=0pF)
FEC
FEC + 22pF
1/f floor +2nd stage
We can numerically change the shaping time to have an optimalresolution
12XY,Q,T measurements with AFTER+ Bordeaux June 17th
2008
Toy montecarlo simulator Toy montecarlo simulator
•Time domain simulation.Time domain simulation.•Noise generator with spectral density = those at preamp output.Noise generator with spectral density = those at preamp output.•““Micromegas” Signal generator.Micromegas” Signal generator.•Model of filter.Model of filter.•Model of sampler.Model of sampler.•Digital Filter (FIR)Digital Filter (FIR)
Exemple:slowing down of the 100ns shaping by convoluting with triangular shape-> 400ns and 800ns effective peak time.
noise decrease.Ballistic deficit reduction(not studied yet)
13XY,Q,T measurements with AFTER+ Bordeaux June 17th
2008
Effect of digital filtering on noise Effect of digital filtering on noise
Black curve: simulated (with the toy MC) ENC for various peaking times, (Fs=50MHz)=> reasonable agreement with measurements.
Red curve: ENC simulated the 100 ns peak time sampled @Fs =50MHz with increasing durationtriangular digital filters.
=> noise reduction equivalent to those obtain with analog filter.In real conditions, would not probablybe so good because of aliased noise (not
simulated here).
14XY,Q,T measurements with AFTER+ Bordeaux June 17th
2008
Fine Timing measurements. Fine Timing measurements.
•Several possible methods: efficiency depending on signal shape and its Several possible methods: efficiency depending on signal shape and its reproducibility.reproducibility.
•optimal filtering (works well if the signal shape is constant).optimal filtering (works well if the signal shape is constant).•deconvolution.deconvolution.•fit of known shape.fit of known shape.•peak finding (with quadratic interpolation).peak finding (with quadratic interpolation).•crossing of linear extrapolation of the rising edge start with baseline.crossing of linear extrapolation of the rising edge start with baseline.•CFD => studied here (linear interpolation method).CFD => studied here (linear interpolation method).
•Expected timing resolution ?Expected timing resolution ?
In the continuous analog world.
t = n . dV/dT.
n proportional to tpeak-1/2 (if dominated by serie noise)
dV/dT proportional to 1/tpeak
classic results
=> A fast shaping is better for timing.Better timing for high S/N
15XY,Q,T measurements with AFTER+ Bordeaux June 17th
2008
Simulations of timing capabilities. Simulations of timing capabilities. • CFD (fraction =0.4) is simulated using :
•Micromegas signal (elementary signal). •No amplitude or shape variation (up to now).•Perfect clock: no clock jitter•Realistic Noise spectral density with white noise and 1/f (T2K)• for various tp
•various noise levels (“nominal”, x2,x3,/2). => various S/N values•various sampling Frequency
S/N in« nominal »condition
16XY,Q,T measurements with AFTER+ Bordeaux June 17th
2008
Simulations of timing capabilities. Simulations of timing capabilities.
Fsample=100MHz
• Time resolution increase ~ linearly with tTime resolution increase ~ linearly with tp p (not expected)(not expected)• Time resolution increase ~linearly with input “noise level”.Time resolution increase ~linearly with input “noise level”.• Problems occur when S/N < 6. Problems occur when S/N < 6. • Very good time resolution can be achieved Very good time resolution can be achieved
17XY,Q,T measurements with AFTER+ Bordeaux June 17th
2008
Timing Simulations. Timing Simulations.
•Time resolutions are flat for sampling frequency down to FTime resolutions are flat for sampling frequency down to Fss.t.tpp =3-4 =3-4
(3 samples on the rising edge)(3 samples on the rising edge)•Resolution far better than TResolution far better than TCKCK/ (12)/ (12)1/2 1/2 are obtained for reasonable S/Nare obtained for reasonable S/N
« nominal » noise(S/N= 22 for tp=200ns)
18XY,Q,T measurements with AFTER+ Bordeaux June 17th
2008
Conclusion and other things to try. Conclusion and other things to try.
•Charge measurement and timing capabilities of AFTER electronics well Charge measurement and timing capabilities of AFTER electronics well understood.understood.
•How can we deal with tracks with angles:How can we deal with tracks with angles:•Pulse deconvolution? => simulation with noise.•What can we learn from shaped signal duration.
•…