Event t_0 from the CLC

Event t_0 from the CLC

Matthew Jones/Riei Ishiziki Purdue University Electronics Simulation in the Photon Transport Monte Carlo

Preamp model Receiver/discriminator circuit CAF driver circuit model Examples Summary January 31, 2005 last update: Jan 30 1 Preamp Model So far, the effect of the preamp has been

ignored, although some degradation in rise-time was included. This was just a wild guess. Need a good preamp model to relate anode charge to output of ADC Particularly important for large pulses. Best studied using SPICE simulation of preamp circuit. Useful check of schematics for the NIM paper. 2 Preamp Model Model for PMT driving preamp (See CDF Note 5358)

Model for PMT driving 50 load Preamp 3 Preamp Model Important to validate the simulation by comparing with real preamp. Input pulse: Gaussian, 1.5ns width, typically 0.01 nC 0.01 nC corresponds to 2080 p.e. when the PMT gain is 3x104

Allows comparison with preamp checkout measurements performed with charge injector. 4 Preamp Model 50 load, 50 mV/div preamp, 50 mV/div output, 500 mV/div Response to 0.01 nC pulse 5

Preamp Model 50 load, 200 mV/div preamp, 200 mV/div output, 1 V/div Soft saturation properly modeled Response to 0.05 nC pulse 6 Preamp Model Gain response parameterized as in CDF Note 5362:

Hard saturation 27 C 37 C Soft saturation 47 C 57 C High gain region 7

Preamp Model Measured parameters: Simulation: 8 Preamp Model Comparison of gain parameters with measured distributions: Small signal differential gain

Large signal differential gain SPICE model Gain switching threshold Width of gain switching region 9

Preamp Model Comparison of node voltages: Small differences are not likely to affect small signal gain. 10 Preamp Model Probable unknowns: Supply voltages in the detector Measure them next time the plugs are open

Temperature in the detector No simulation of parasitic capacitance Parameters for gain switching diode model Qualitative behavior seems reasonable. Small signal response agrees well with measurements and should be adequately described. 11 Preamp Model SPICE3 simulation now interfaced with

photon transport Monte Carlo: Response to 1 MIP through bar at z=0. This is an important achievement! 12 Receiver/discriminator model PMT + base model Input to AD96687

comparator Preamp sub-circuit Input to CAF driver AD8131 model 13 CAF Driver Circuit Model Input pulse CAF model

Gate ECL output model 14 TOAD Electronics Still should perform more validation: Compare with production TOAD board node voltages Still not simulating signal cable (22 m attenuation length) and RF transformer

Need to determine phase of CAF clock Include parasitic capacitances on TOAD and connector inductances to CAF card 15 Software Interface Interfaced with photon transport MC: PMT class constructs SPICE3 model for current pulse at the anode. System call to invoke SPICE3 with circuit models Output vectors read from binary file Currently stored as non-persistent TGraph objects

Simulation is fast (few seconds) compared with photon propagation 16 Example: 1 MIP at z=100 cm Voltage pulse at preamp input Voltage pulse at preamp output Discriminator input CAF driver input CAF driver gate

Current into CAFE about 2000 ADC counts 17 Another example: Two tracks hit simultaneously at z=100 cm and z=-50cm: 18 Yet another example: Two tracks in different 132 ns bunch

crossings: 19 Electronics Simulation It is now possible to study: Absolute scale of discriminator threshold Functional form of time slewing correction ADC bias due to multiple hits Baseline shifts from hits in earlier bunch crossings (luminosity dependence of ADC) ADC response to monopoles, MIPs, etc.

Limiting factors will probably come from the PMT parameters (photocathode sensitivity, absolute gain) and scintillator. 20 Summary SPICE3 models: Preamp: good shape now Discriminator: should be okay Use simulation instead of parameterized model? Need to check threshold circuit in more detail. CAFE driver: Predicted ADC counts have the right

order of magnitude! Still need to work out the phase of the CAF integration gate Now we will have to subtract pedestals in the simulation Real limitation probably comes from things we cant measure (PMT and scintillator properties). 21

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