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Description
The Light Dark Matter eXperiment (LDMX) is a fixed-target electron-beam experiment aimed at observing light dark matter (LDM) production through missing momentum. LDMX’s electronic and hadronic calorimeter uses the HGCROC ASIC from the CMS experiment for electronic readout. This work focuses on the characteristic behavior of the ASIC’s Analogue to Digital Converter (ADC). The linearity of ADC and Time Over Threshold (TOT) was studied with a series of controlled charge injections. The linearity of the ADC was investigated by tracking the behavior of the ADC pulse amplitude upon varying the injected charge. The ADC response to an 8pF (low-range) and a 500fF (high-range) capacitor portrayed linear behavior. A correction was applied to the high-range measurements to align with the obtained low-range values, allowing for better comparison of the injected charge along the circuit. The TOT, expressed as the time spanned by a plateau region produced as a result of saturation of the ADC, was expected to increase linearly with the amplitude of the pulse. This allows for the expansion of the linearity of the ADC in the saturated regime. The TOT threshold was correlated to an ADC value by identifying when 50% of the signals triggered the TOT readout.
