IEEE Instrumentation & Measurement - September 2023 - 13

Potential Use of State-of-the-Art
TDCs for Particle Identification in
Particle Physics Experiments
Moisés Arredondo-Velázquez, Lucio Rebolledo-Herrera,
Benito De Celis Alonso, and Eduardo Moreno-Barbosa
T
ime-to-Digital Converters (TDCs) are instruments
used to measure time intervals from digital signals
accurately. They play an essential role in areas such as
Light Detection and Ranging (LiDAR), Positron Emission Tomography
(PET) [1] and Particle Physics Experiments (PPE)
[2]. Particularly, PPE involves the identification of particles
resulting from collisions in accelerators. The estimation is carried
out by measuring their Time of Flight (ToF) and deposited
charge in the scintillator materials, becoming a radiation detector,
as observed in Fig. 1.
In PPE, accelerators boost particles to high energies to collide
inside detectors. Scintillating materials detect the resulting
radiation by creating photons (scintillation) inside these materials,
whose amount is proportional to the deposited energy of
incident radiation. Silicon Photo Multipliers (SiPMs) or Photo
Multiplier Tubes (PMTs) are used as photosensors to generate
analog electrical signals from which it is possible to obtain
information about these particles, such as the charge and position
where the collision occurred. Nevertheless, signal
conditioning is mandatory before using TDCs; this includes
a preamplification and a shaper stage. The latter filters or rejects
the photosensors signals if these are inadequate due to
pile-up, noise, or saturation. Discriminators, which act as voltage
comparators, generate digital signals for the TDC, keeping
the pulse width from the analog inputs. A single TDC can
measure either the ToF (represented as P) or the digital signal
pulse width (W) that represents the time photosensors signal
is over discriminator threshold Th (Time-Over-Threshold
(TOT)). Both types of measurements are essential in particles
identification [3, 4]. An example of a multi-channel TDC, with
input signals such as IS n
n∀= ... ,, , ,N is shown in Fig. 2. Each
12
signal represents incident radiation in the scintillator. Additionally,
a trigger signal of arbitrary width and in-phase with
the first arrived signal IS0 may be generated to indicate that a
collision occurred.
Typical approach for width or ToF measurement consists
of coarse and fine counting. Coarse counting (CC) is based on
the fact that W or P are longer than the TDC clock period (expressed
as T) and can be quantified by means of clock cycles
September 2023
Preamp
Shaper
Th
Discriminator
TDC
Pulse width
TDC
Pulses Phase
Fig. 1. Representation of typical stages for particles identification in PPE.
counting. Every counting is realized through a synchronous
digital counter that increases its count when ISn is high and a
rising edge in the clock signal occurs. Thus, CC is expressed
in terms of the number of clock cycles (C). On the other hand,
fine counting (also called fine measurement (FM)) is performed
via asynchronous circuits where ISn is propagated
throughout delay elements (DEs) that act as gauges that indicate
how far ISn was propagated. Once the clock rising
Photosensors
Scintillators
Preamp
Shaper
Th
Discriminator
TDC
Pulse width
T1
CLK
IS0
IS1
ISn
TR
(1)
T1
P0
P1
Pn
Wn
T
Fig. 2. Example of input signals for time measurement.
IEEE Instrumentation & Measurement Magazine
1094-6969/23/$25.00©2023IEEE
13
(n)
T1
(2)
T2
(n)
T2
(1)
T2
W0
W1
(2)

IEEE Instrumentation & Measurement - September 2023

Table of Contents for the Digital Edition of IEEE Instrumentation & Measurement - September 2023

Contents
IEEE Instrumentation & Measurement - September 2023 - Cover1
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IEEE Instrumentation & Measurement - September 2023 - Contents
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