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4 * Author: The ALICE Off-line Project. *
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16 /** @file AliFMDDigitizer.cxx
17 @author Christian Holm Christensen <cholm@nbi.dk>
18 @date Mon Mar 27 12:38:26 2006
19 @brief FMD Digitizers implementation
22 //////////////////////////////////////////////////////////////////////////////
24 // This class contains the procedures simulation ADC signal for the
25 // Forward Multiplicity detector : Hits->Digits
32 // - ADC count in this channel
34 // As the Digits and SDigits have so much in common, the classes
35 // AliFMDDigitizer and AliFMDSDigitizer are implemented via a base
36 // class AliFMDBaseDigitizer.
38 // +---------------------+
39 // | AliFMDBaseDigitizer |
40 // +---------------------+
43 // +----------+---------+
45 // +-----------------+ +------------------+
46 // | AliFMDDigitizer | | AliFMDSDigitizer |
47 // +-----------------+ +------------------+
49 // These classes has several paramters:
53 // (Only AliFMDDigitizer)
54 // Mean and width of the pedestal. The pedestal is simulated
55 // by a Guassian, but derived classes my override MakePedestal
56 // to simulate it differently (or pick it up from a database).
59 // The dymamic MIP range of the VA1_ALICE pre-amplifier chip
62 // The largest number plus one that can be stored in one
63 // channel in one time step in the ALTRO ADC chip.
66 // How many times the ALTRO ADC chip samples the VA1_ALICE
67 // pre-amplifier signal. The VA1_ALICE chip is read-out at
68 // 10MHz, while it's possible to drive the ALTRO chip at
69 // 25MHz. That means, that the ALTRO chip can have time to
70 // sample each VA1_ALICE signal up to 2 times. Although it's
71 // not certain this feature will be used in the production,
72 // we'd like have the option, and so it should be reflected in
75 // These parameters are fetched from OCDB via the mananger AliFMDParameters.
77 // The shaping function of the VA1_ALICE is generally given by
79 // f(x) = A(1 - exp(-Bx))
81 // where A is the total charge collected in the pre-amp., and B is a
82 // paramter that depends on the shaping time of the VA1_ALICE circut.
84 // When simulating the shaping function of the VA1_ALICe
85 // pre-amp. chip, we have to take into account, that the shaping
86 // function depends on the previous value of read from the pre-amp.
88 // That results in the following algorithm:
91 // FOR charge IN pre-amp. charge train DO
92 // IF last < charge THEN
93 // f(t) = (charge - last) * (1 - exp(-B * t)) + last
95 // f(t) = (last - charge) * exp(-B * t) + charge)
97 // FOR i IN # samples DO
98 // adc_i = f(i / (# samples))
105 // pre-amp. charge train
106 // is a series of 128 charges read from the VA1_ALICE chip
109 // is the number of times the ALTRO ADC samples each of the 128
110 // charges from the pre-amp.
112 // Where Q is the total charge collected by the VA1_ALICE
113 // pre-amplifier. Q is then given by
119 // where E is the total energy deposited in a silicon strip, R is the
120 // dynamic range of the VA1_ALICE pre-amp (fVA1MipRange), e is the
121 // energy deposited by a single MIP, and S ALTRO channel size in each
122 // time step (fAltroChannelSize).
124 // The energy deposited per MIP is given by
128 // where M is the universal number 1.664, rho is the density of
129 // silicon, and w is the depth of the silicon sensor.
131 // The final ADC count is given by
135 // where P is the (randomized) pedestal (see MakePedestal)
137 // This class uses the class template AliFMDMap<Type> to make an
138 // internal cache of the energy deposted of the hits. The class
139 // template is instantasized as
141 // typedef AliFMDMap<std::pair<Float_t, UShort_t> > AliFMDEdepMap;
143 // The first member of the values is the summed energy deposition in a
144 // given strip, while the second member of the values is the number of
145 // hits in a given strip. Using the second member, it's possible to
146 // do some checks on just how many times a strip got hit, and what
147 // kind of error we get in our reconstructed hits. Note, that this
148 // information is currently not written to the digits tree. I think a
149 // QA (Quality Assurance) digit tree is better suited for that task.
150 // However, the information is there to be used in the future.
153 // Latest changes by Christian Holm Christensen
155 //////////////////////////////////////////////////////////////////////////////
158 // | A(-1 + B + exp(-B))
159 // | f(x) dx = ------------------- = 1
163 // and B is the a parameter defined by the shaping time (fShapingTime).
165 // Solving the above equation, for A gives
168 // A = ----------------
171 // So, if we define the function g: [0,1] -> [0:1] by
174 // | Bu + exp(-Bu) - Bv - exp(-Bv)
175 // g(u,v) = | f(x) dx = -A -----------------------------
179 // we can evaluate the ALTRO sample of the VA1_ALICE pre-amp between
180 // any two times (u, v), by
183 // B Bu + exp(-Bu) - Bv - exp(-Bv)
184 // C = Q g(u,v) = - Q ---------------- -----------------------------
185 // -1 + B + exp(-B) B
187 // Bu + exp(-Bu) - Bv - exp(-Bv)
188 // = - Q -----------------------------
192 #include <TTree.h> // ROOT_TTree
193 #include <TRandom.h> // ROOT_TRandom
194 #include "AliFMDDebug.h" // Better debug macros
195 #include "AliFMDDigitizer.h" // ALIFMDDIGITIZER_H
196 #include "AliFMD.h" // ALIFMD_H
197 #include "AliFMDDigit.h" // ALIFMDDIGIT_H
198 #include "AliFMDParameters.h" // ALIFMDPARAMETERS_H
199 #include <AliRunDigitizer.h> // ALIRUNDIGITIZER_H
200 #include <AliRun.h> // ALIRUN_H
201 #include <AliLoader.h> // ALILOADER_H
202 #include <AliRunLoader.h> // ALIRUNLOADER_H
204 //====================================================================
205 ClassImp(AliFMDDigitizer)
207 //____________________________________________________________________
209 AliFMDDigitizer::OutputTree(AliLoader* outFMD, AliFMD* fmd)
211 // Load digits from the tree
212 outFMD->LoadDigits("update");
214 // Get the tree of digits
215 TTree* digitTree = outFMD->TreeD();
217 outFMD->MakeTree("D");
218 digitTree = outFMD->TreeD();
223 TClonesArray* digits = fmd->Digits();
225 AliError("Failed to get digits");
228 AliFMDDebug(1, ("Got a total of %5d digits", digits->GetEntries()));
230 // Make a branch in the tree
231 fmd->MakeBranchInTree(digitTree, fmd->GetName(), &(digits), 4000, 0);
232 // TBranch* digitBranch = digitTree->GetBranch(fmd->GetName());
235 write = digitTree->Fill();
236 AliFMDDebug(1, ("Wrote %d bytes to digit tree", write));
238 // Write the digits to disk
239 outFMD->WriteDigits("OVERWRITE");
240 outFMD->UnloadHits();
241 outFMD->UnloadDigits();
243 // Reset the digits in the AliFMD object
247 //____________________________________________________________________
249 AliFMDDigitizer::MakePedestal(UShort_t detector,
252 UShort_t strip) const
255 AliFMDParameters* param =AliFMDParameters::Instance();
256 Float_t mean =param->GetPedestal(detector,ring,sector,strip);
257 Float_t width =param->GetPedestalWidth(detector,ring,sector,strip);
258 return UShort_t(TMath::Max(gRandom->Gaus(mean, width), 0.));
261 //____________________________________________________________________
263 AliFMDDigitizer::AddDigit(AliFMD* fmd,
272 Short_t count4) const
275 fmd->AddDigitByFields(detector, ring, sector, strip,
276 count1, count2, count3, count4);
279 //____________________________________________________________________
281 AliFMDDigitizer::CheckDigit(AliFMDDigit* digit,
283 const TArrayI& counts)
285 // Check that digit is consistent
286 AliFMDParameters* param = AliFMDParameters::Instance();
287 UShort_t det = digit->Detector();
288 Char_t ring = digit->Ring();
289 UShort_t sec = digit->Sector();
290 UShort_t str = digit->Strip();
291 Float_t mean = param->GetPedestal(det,ring,sec,str);
292 Float_t width = param->GetPedestalWidth(det,ring,sec,str);
293 UShort_t range = param->GetVA1MipRange();
294 UShort_t size = param->GetAltroChannelSize();
295 Int_t integral = counts[0];
296 if (counts[1] >= 0) integral += counts[1];
297 if (counts[2] >= 0) integral += counts[2];
298 if (counts[3] >= 0) integral += counts[3];
299 integral -= Int_t(mean + 2 * width);
300 if (integral < 0) integral = 0;
302 Float_t convF = Float_t(range) / size;
303 Float_t mips = integral * convF;
304 if (mips > Float_t(nhits) + .5 || mips < Float_t(nhits) - .5)
305 Warning("CheckDigit", "Digit -> %4.2f MIPS != %d +/- .5 hits",
309 //____________________________________________________________________