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A couple of test items

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A couple of test items

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  1. A couple of test items Paul Dauncey, Imperial College London Paul Dauncey

  2. Monostable lengths • Hits above threshold should give fixed length output pulse • Given by monostable, common design to shapers and samplers • Length of output pulse controlled by bias settings from DACs on Vladimir’s PCB • I12_MSOBIAS1 and I34_MSOBIAS1 for shapers and samplers respectively • Samplers also have reset monostable, which needs to be longer than the hit monostable; I34_MSOBIAS2 • Ideally monostable hit length ~1.1 of BX period; balance efficiency against memory use • Looked into the monostables in the bulk • Thought they might be the cause of some of oddities seen by Jamie B Paul Dauncey

  3. Monostables on test structures • Jamie C measured monostable hit output on test structure • Controlled by separate DACs • Can see the length directly on a scope Minimum pulse ~180ns Default DAC=2048 gives pulse ~500ns Paul Dauncey

  4. Monostables on bulk pixels • Cannot measure directly; can only see hits in memory • Count consecutive timestamps to measure “BX length” of hit for every channel • Current firmware BX frequency is 2.5MHz (i.e. 40MHz/16) so BX period is 400ns Length in BX units Looks similar to test structure  DAC Paul Dauncey

  5. Characterise slope • Do rough fit to exponential of profile histogram • Not “good” fit but robust Paul Dauncey

  6. Uniformity is not good • Plot exponential slope vs pixel location: 168*x+y • Shapers are < 14112, samplers the rest X=000, Y=002 Paul Dauncey

  7. Other pixels Sampler: did not change reset length Paul Dauncey

  8. Reproduce at Imperial? • Rerun with lower threshold and changing sampler resets • Currently cannot get same result • Even for good pixel Paul Dauncey

  9. DAQ speed • Limited by data rate from sensor Implies a rate of >100Hz if running normally ~200 words Paul Dauncey