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VELO ADC vs Charge Calibration

VELO ADC vs Charge Calibration . Jianchun Wang April 16, 2008. This is an update to the presentation at April 11 st VELO Group Meeting. A new scan data of larger charge range has been taken. Further more detailed studies. Introduction.

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VELO ADC vs Charge Calibration

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  1. VELO ADC vs Charge Calibration Jianchun Wang April 16, 2008 This is an update to the presentation at April 11st VELO Group Meeting. A new scan data of larger charge range has been taken. Further more detailed studies.

  2. Introduction • To determine the ADC readout value as a function of charge collected. • Different gains for different channels. • Non-linearity with large signal. • Will be used in hit position reconstruction, and MC simulation (by Tomasz Szumlak & David Hutchcroft). • This calibration was planned some time ago but the system was not available until recently. • Olaf Behrendt & Stefano De Capua managed to take a small scaled test pulse run. Another run with larger charge range is taken per request. • A dummy hybrid is used. • Charge injected with 41 different DAC(Itp) values: 0, 5, 10, …., 200. • Events per Itp DAC setting: 1000. • Only 2 channels per link are injected (4 & 23). • Polarity of signal changes for consecutive events. Jianchun Wang

  3. Raw ADC vs Testpulse DAC Saturation with large pulse. Straight line does not fit. Each point is obtained from fit of raw ADC distribution to a Gaussian function. Use ADC spread as error (over estimated). Average Raw ADC Readout Itp DAC value increases by 5 per step. Negative DAC  Negative polarity DQ = 1025 e / (DAC value). Largest charge 205Ke ~ 9 MIPS. Testpulse DAC Value Jianchun Wang

  4. ADC Readout Issue at DAC=0 Estimate pedestal from 10 neighboring points Average Raw ADC Readout Testpulse DAC Value Lower than projection from neighboring points Point (DAC=0) excluded from any further fit ADC(DAC=0) - Pedestal Jianchun Wang

  5. Charge Offset Issue One line Number of Channels ADC Readout – Fit to Straight Line Two lines with offset in the middle Charge Offset (Ke) Testpulse DAC Value Jianchun Wang

  6. Functions Used in Fit Slope Scale ADC Readout - Pedestal Scale Charge Center Asymmetric, Not good for  when P>0 Jianchun Wang

  7. Fit of ADC vs Charge to Functions Hyperbolic tangent function Raw ADC - Pedestal Raw ADC – Pedestal - Fit Modified hyperbolic tangent function Injected Charge (Ke) Injected Charge (Ke) Jianchun Wang

  8. Fit Parameters (I) Center [Ke] Scale [ADC counts] Slope [ADC/Ke] Jianchun Wang

  9. Fit Parameters (II) Scale [ADC counts] Slope [ADC/Ke] Center [Ke] P Jianchun Wang

  10. ADC vs Charge Modified hyperbolic tangent Scale = 302.9 Slope = 1.594 Center = -28.13 P = 0.3032 2 channels of link 0 Raw ADC - Pedestal Hyperbolic tangent function Scale = 262.1 Slope = 1.709 Center = 7.35 Charge (Ke) All 128 channels of 64 links in a hybrid Jianchun Wang

  11. Summary • Saturation effect can be seen with a test pulse run that covers inject charge range of -205Ke to 205 Ke. • A modified hyperbolic tangent function fits ADC vs charge distribution better than previously proposed hyperbolic tangent function. • We will calibrate each individual channel in the final system. • Gain of each channel will be adjusted to be equal based on the testpulse calibration. Jianchun Wang

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