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A couple of test items

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

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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

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