Tests of large charge injection with external capacitor

• Purpose

  Charge injection tests with an external capacitor were performed to investigate crosstalk between strips on SSDs, channels on GTFE analog circuits when large charge events issued.
  

• Method

  We used a full ladder - miniMCM test system. A 2.2 pF capacitor was attached to the end of the strip #96, the opposite side of the ladder from the readout electronics. A test pulse with a step function was sent to the capacitor and hit strip data was read out repeatedly. We scanned trigger acknowledge delay from the rising time of the calibration strobe pulse, and investigated the development of hit pattern (crosstalk) during the comparator-on.
  

• Charge injections by external capacitor: 2.2pF * 40mV = 88fC

  External charges which corresponds to 88 fC were injected to the strip #96 via the external capacitor. The channels #0--#383 were connected to the strips on the ladder. The channels #384--#447 were opened. The figure below shows the time dependence of the hit pattern. We see that 3 adjacent strips of #96 were affected by injection charge. The right panel is the magnification of the left panel around the strip #96. The unit of TACK_DELAY is a clock cycle [/50ns]. The TOT for the signal is about 2500 * 50ns = 125us, which is a little longer than that in LAT-TD-01090 p.18, 80us, but would not differ so largely. We can also see that the noise level is a little high around the edges of the detector, channels #0 and #383.
  

• Charge injection by external capacitor: 2.2pF * 400mV = 880fC

  External charges which corresponds to 880 fC were injected to the strip #96 via an external capacitor. The TOT for the signal is about 3000 * 50ns = 150us, which is consistent with that in LAT-TD-01090 p.18.
  
  

• Another sample of test results: charge injection by internal calibration system and external capacitor

  To check the test system, internal calibration pulses of about 1 MIP are injected to the strips #48, #112, #176, #240, #304, #368, #432 simultaneously with the external pulse. We see that the TOT for 1 MIP is about 160*50ns = 8us.