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DLD4040 R2.55 & R3.54 Manual | Surface Concept GmbH
5.2 Basic Operational Modes of the Delayline Detector
5.2.1 2D(x, y) Area Detection
The arrival times of pulses per event at the 4 ends of the DLD meander/quadrant are subtracted in order
to determine a position in x and y (x: tx1-tx2; y: ty1-ty2). The 4 TDC stop signals are grouped internally in
pairs to form the x- and y-coordinates. All DLD software adjustments are done by the end-user software
according to the user’s chosen parameters.
5.2.2 3D(x, y, t) Time Resolved Imaging
The delayline detector may measure all events in temporal reference to an external clock. For this mode,
the user needs to start the TDC by an external clock, providing a low jitter LVTTL signal to the start input
of the TDC.
Time measurements are performed by summing up the arrival times of pulses at the end of the DLD me-
anders, i.e. the same results which are used to determine positions for each event are summed. It is pos-
sible to sum only tx1 and tx2 (tsumx) or ty1 and ty2 (tsumy), because both sums should carry the same
temporal information of a time related experiment. The total sum t(DLD) of all four time measurements
(tx1, tx2, ty1, ty2) may be a good choice as well. The results of all those time sums correspond to t(sum) =
t(offset) + t(hit), where t(hit) is the interesting time (e.g. ToF) in a given experiment and t(offset) is a device
related constant, which depends on cable lengths, electronics propagation times, experimental setup etc.
Therefore, it is possible to completely determine position and time of each event from only 4 precise time
measurements.
The software can group all measured time sums in plain 1D time histograms, which are valid for the chosen
region of interest (ROI) with the correct time bin unit. The time bin unit for each single readout channel
is around 27ps, but due to the calculation of the tsums and t(DLD), the time axis is expanded virtually
(simplified expression). Therefore the channel width in the 1D histogram is different for the tsumx, tsumy
and t(DLD) histograms. The correct value for a current setting is always shown by the software. The t(DLD)
signature can be used in order to setup the regions of interest in time for measurements of time resolved
images. The software is able to sample 3D histograms as image stacks in time, where each image corre-
sponds to one channel width of the t(DLD) time histogram.
5.3 Data Acquisition
Each readout line of the detector anode is connected to a fast amplifier followed by a constant fraction
discriminator (CFD) for pulse shaping. They are encapsulated inside the pulse processing electronics (ACU
= Amplifier-CFD-Unit or AU = Amplifier-Unit). The main function of the CFD is digital pulse discrimination,
ideally without any time-walk even at varying pulse heights. A time-to-digital converter (TDC) behind
these chains serves as stop-watch for arrival time measurements.
