1. 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.

2. Jianchun Wang2 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.

3. Jianchun Wang3 Testpulse DAC Value Average Raw ADC Readout 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). Itp DAC value increases by 5 per step. Negative DAC  Negative polarity  Q = 1025 e / (DAC value). Largest charge  205Ke ~  9 MIPS.

4. Jianchun Wang4 ADC Readout Issue at DAC=0 Testpulse DAC Value Average Raw ADC Readout Lower than projection from neighboring points Point (DAC=0) excluded from any further fit Estimate pedestal from 10 neighboring points ADC (DAC=0) - Pedestal

5. Jianchun Wang5 Charge Offset Issue Charge Offset (Ke) Number of Channels Testpulse DAC Value ADC Readout – Fit to Straight Line One line Two lines with offset in the middle

6. Jianchun Wang6 Functions Used in Fit Scale Center Slope Charge ADC Readout - Pedestal Asymmetric, Not good for  when P>0 Scale

7. Jianchun Wang7 Fit of ADC vs Charge to Functions Injected Charge (Ke) Raw ADC - Pedestal Injected Charge (Ke) Raw ADC – Pedestal - Fit Hyperbolic tangent function Modified hyperbolic tangent function

8. Jianchun Wang8 Fit Parameters (I) Scale [ADC counts]Slope [ADC/Ke] Center [Ke]

9. Jianchun Wang9 Fit Parameters (II) Scale [ADC counts]Slope [ADC/Ke]Center [Ke] P

10. Jianchun Wang10 ADC vs Charge Charge (Ke) Raw ADC - Pedestal 2 channels of link 0 Modified hyperbolic tangent Scale = 302.9 Slope = 1.594 Center = -28.13 P = 0.3032 All 128 channels of 64 links in a hybrid Hyperbolic tangent function Scale = 262.1 Slope = 1.709 Center = 7.35

11. Jianchun Wang11 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.