Dynamic Time Over Threshold Method

Abstract

The time over threshold (TOT) method has several advantages over direct pulse height analysis based on analog to digital converters (ADCs). A key advantage is the simplicity of the conversion circuit which leads to a high level of integration and a low power consumption. The TOT technique is well suited to build multi-channel readout systems for pixelated detectors as described in our previous work that also exploits the Pulse Width Modulation (PWM) method. The main limitation of the TOT technique is that the relation between the input charge to be measured and the width of the encoded pulse is strongly non-linear. Dynamic range limitation is also an issue. To address these aspects, we propose a new time over threshold conversion circuit where the threshold of the comparator is dynamically changed instead of being constant. We call this scheme the "dynamic TOT method". We show that it improves linearity and dynamic range. It also shortens the duration of measured pulses leading to higher counting rates. We present a short analysis that explains how the ideal linear input charge to TOT transfer function can theoretically be obtained. We describe the results obtained with a test circuit built from discrete components and present several of the spectrums obtained with crystal detectors and a radioactive source. The proposed method can be used for applications like Positron Emission Tomography (PET) that require moderate energy resolution.Index Terms-Dynamic time over threshold (TOT), positron emission tomography (PET), pulse width modulation (PWM), time over threshold (TOT).

A low-power Read-Out Circuit and low-cost assembly of nanosensors onto a 0.13 μm CMOS Micro-for-Nano chip

“…On the contrary, the other flow implies a mixed-signal design that converts resistance and capacitance to the time domain. This technique can be implemented using a lowcomplexity architecture as PWM circuits [12], Time-overThreshold [14], [15], resistance-to-period converters [16] and oscillators [17], [18]. These circuits generates quasi-digital outputs that are compliant with commercial digital electronics (e.g.…”

Analog and digital signal processing method using multi‐time‐over‐threshold and FPGA for PET

“…However, the resulting performance of TOT suffers from a distortion in the energy spectrum degrading energy resolution because of nonlinear input energy to output pulse width conversion. [7][8][9][10][11][12][13][14][15][16][17] MVT is also a digital sampling method, analogous to TOT, to generate samples of an event waveform of PET but employs multiple thresholds to extract energy and time information of a PET event. This method showed that implementing TOT with multiple triggering thresholds could overcome the problems inherent to nonlinear performance of TOT.…”

“…Therefore, compared with other digital sampling methods, such as DRS and TOT, MVT can provide high performance because it has shorter conversion time for storing amplitudes than DRS achieving high count rate and can obtain more samples per detector output pulse than TOT method improving nonlinearity of energy resolution. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17] For design of PET systems using digital sampling methods, such as TOT, DRS, and MVT, a digital DAQ system usually has been employed. These systems consist of an analog-to-digital converter (ADC), time-to-digital converter (TDC), and field-programmable-gate-array (FPGA) for extracting energy and timing information for a detected event.…”

A prototype of aerial radiation monitoring system using an unmanned helicopter mounting a GAGG scintillator Compton camera

“…This paper introduces the concept, design, fabrication and performance of a prototype imaging system with a high spatial resolution and efficiency for mapping radiation distribution in Fukushima. Section 2 discusses the design and fabrication of the system, including electronics using dToT [11] which is firstly applied to a Compton camera. Section 3 introduces the experiments and results.…”