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STJ Quick Start Guide v 2.01
April 1, 2021
Page 20
Fig 10: This plot shows the Scaled Energy response to the on-board pulser signal with the Decay Time set properly: The waveform
is trapezoidal, and properly damped
ADJUST THE ADC OFFSET
Each ADC channel has a dedicated DAC which operates under computer control to set the ADC offset. By
default, the ADC is biased near mid-range. If data is acquired with this default setting, half of the ADC
range is wasted, and the effective dynamic range is unnecessarily constrained.
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It is very important to adjust the ADC Offset before acquiring MCA or list-mode data (but after
the STJ bias voltages have been adjusted)!
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The offset value, with a range of 1-8191, corresponds directly to the 12-bit ADC, and should be
set as low as possible but high enough that the ADC waveform NEVER drops below 0 due to
noise. We typically set the offset to 128, which is roughly 3% above the ADC minimum, and
which makes 97% of the ADC range available for pulses.
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The special value 0 resets the DAC to mid-range
MCA PANEL
The MCA panel is used to acquire histogrammed energy data and run statistics. It includes Preset Run
settings and a Region of Interest (ROI) Calibration tool. During an MCA acquisition run incoming events for
each channel are stored according to their measured energy in a separate histogram.
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Press the Start Run button to begin acquisition, with an optional Preset Run constraint
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Press the Stop Run button to end acquisition