A 1.9 ps-rms Precision Time-to-Amplitude Converter With 782 fs LSB and 0.79%-rms DNL

Measuring a time interval in the nanoseconds range has opened the way to 3-D imaging, where additional information as distance of objects light detection and ranging (LiDAR) or lifetime decay fluorescence-lifetime imaging (FLIM) is added to spatial coordinates. One of the key elements of these systems is the time measurement circuit, which encodes a time interval into digital words. Nowadays, most demanding applications, especially in the biological field, require time-conversion circuits with a challenging combination of performance, including sub-ps resolution, ps precision, several ns of measurement range, linearity better than few percent of the bin width (especially when complex lifetime data caused by multiple factors have to be retrieved), and operating rates in the order of tens of Mcps. In this article, we present a time-to-amplitude converter (TAC) implemented in a SiGe 350 nm process featuring a resolution of 782 fs, a minimum timing jitter as low as 1.9 ps-rms, a DNL down to 0.79% LSB-rms, and conversion rate as high as 12.3 Mcps. With an area occupation of 0.2 mm2 [without PADs and digital-to-analog converter (DAC)], a FSR up to 100 ns, and a power dissipation of 70 mW, we developed a circuit suitable to be the core element of a densely integrated, faster and high-performance system

Double-Terminal Quenching Topology for Threefold After-Pulsing Reduction: Model and Experimental Validation

Single-Photon Avalanche Diodes (SPADs) have emerged as crucial devices across a multitude of applications, ranging from Fluorescence Lifetime Imaging (FLIM) to Quantum technologies and LiDAR systems. The increasing demand of fastening the acquisition rate of these application has spurred significant interest in minimizing the SPAD dead-time to a few nanoseconds. However, attempts to minimize its duration often exacerbate the after-pulsing phenomenon, posing a significant challenge in optimizing system performance. In this paper, we propose a novel strategy to address this trade-off. We introduce a method that exploits passive or active quenching at the cathode terminal of SPADs, combined with an Active Quenching Circuit at the anode node. This combined approach aims at mitigating after-pulsing effects while simultaneously minimizing dead time. We developed a comprehensive model and validation methodology to rigorously evaluate the effectiveness of this strategy. Finally, we demonstrate how it is possible to achieve a strong reduction in after-pulsing compared to standard approaches

Morphological and genetic aspects of Marfan Syndrome as demonstrated by a case of death during pregnancy with the discovery of two de novo missense mutations in the FBN1 gene

Marfan Syndrome (MFS) is an autosomal dominant disease caused in most cases by mutations in the FNB1 gene, which encodes for fibrillin 1. MFS does not alway shows typical phenotypic signs. Indeed, the occurrence of sudden death of unknown cause is increasingly seen in young adults without ante mortem preexisting pathology to explain the event. In many cases the diagnosis of Marfan Syndrome (MFS) is carried out post mortem, especially in cases where the disease’s external phenotype is absent. Here is reported a case of a young woman who died during a twin pregnancy investigated with medico-legal and forensic anthropological procedures. The autopsy showed the absence of a typical marfanoid habitus and the presence of a dissecting aneurysm of the aorta with histopathological degeneration of the aortic elastic fibers. The genetic investigation revealed two previously undetected de novo mutations of the FBN1 gene: c.T6181C: p.C2061R and c.G1415A: p.C472Y. This new mutations, together with a comprehensive analysis, demonstrates the existence of a causal relationship between these mutations and the dissecting aneurysm of the aorta. This also stresses the importance of a combined multidisciplinary approach to this condition which includes morphological and genetic studies

Transfer Bandwidth Optimization for Multichannel Time-Correlated Single-Photon-Counting Systems Using a Router-Based Architecture: New Advancements and Results

Time-correlated single-photon counting (TCSPC) is a powerful technique for time-resolved measurement of fast and weak light signals used in a variety of scientific fields, including biology, medicine, and quantum cryptography. Unfortunately, given its repetitive nature, TCSPC is recognized as a relatively slow technique. In the last ten years, attempts have been made to speed it up by developing multichannel integrated architectures. Yet, for the solutions proposed thus far, the measurement speed has not increased proportionally to the number of channels, reducing the benefits of a multichannel approach. Recent theoretical studies and prototypes have shown that it is possible to implement a new multichannel architecture, so-called router-based architecture, capable of optimizing the efficiency of data transfer from the integrated chip to the data processor, increasing the overall measurement speed. However, the first implementations failed to achieve the theoretical results due to implementation flaws. In this paper, we present a new logic for the router-based architecture that can operate at the same laser frequency and solve the issues of the previous implementation. Alongside the new logic, we present a new integrated low-jitter delay line combined with a new method for timing-signal distribution that allows the proper management of the pixel timing information. The new implementation is a step closer to realizing a router-based architecture that achieves the expected theoretical results. Simulations and bench tests support the results here reported

Integrated Active Quenching Circuit for high-rate and distortionless SPAD-based time-resolved fluorescence applications

: Time-Correlated Single Photon Counting (TCSPC) is a pivotal technique in low-light-detection applications, renowned for its exceptional sensitivity and bandwidth, widely used in Fluorescence Lifetime Imaging Microscopy (FLIM) and quantum optics. Despite its features, TCSPC is significantly hindered by the pile-up effect, which may distort measurements at high photon-detection rates. Overcoming pile-up is challenging, with traditional solutions often involving complex post-processing or multichannel systems, complicating the TCSPC setup and limiting performance. A breakthrough to overcome this issue is matching the photodetector dead time to an integer multiple of the laser period, obtaining a distortionless histogram even at high illumination conditions. Building on this concept, we present an Active Quenching Circuit (AQC) developed in high-voltage 150 nm technology, achieving unprecedented control over the Single Photon Avalanche Diode (SPAD) dead time. Our design compensates for Process, Voltage, and Temperature (PVT) variations, ensuring ultra precise and robust dead time tuning. The presented AQC achieves a dead-time resolution of 50 ps suitable for time-resolved experiments within a selectable range of laser frequencies from 20 to 100 MHz, maintaining close-to- ideal linearity in dead-time control. Experimental validations through fluorescence measurements reveal a distortion as low as 0.43% under elevated count-rate conditions, highlighting the efficacy of our circuit in overcoming the pile-up limitation

Fully-integrated multifunctional fast time to amplitude converter for high-performance timing applications

Timing measurements with single photon detectors have acquired a prominent role in many applications, especially where they allow the recovery of faint light signals in harsh environments. We present a new fully-integrated multifunctional Time-to-Amplitude Converter (TAC), featuring 8 channels with a full scale range up to 100ns and a linearity better than 1% of the LSB peak to peak. The maximum speed of the converter is obtained in the Fast-TAC configuration (80MHz), while the precision of the converter can be maximized by exploiting multiple channels to perform the same conversion, achieving an overall jitter as low as 1.4ps

Configurable multichannel Time-to-Amplitude Converter for advanced TCSPC applications

In this work, we present the configurable Fast-Time-to-Amplitude Converter (FTAC), a versatile and completely integrated multichannel timing device constituted by 8 high-performance Time-to-Amplitude Converters (TACs) and a smart front-end logic. The designed converter can not only provide state-of-the-art performance in terms of conversion frequency (up to 100Mcps) and timing precision (down to 1.1ps rms, i.e. 2.6 ps Full Width at Half Maximum), but also a unique flexibility to the end user, who can select the most suitable configuration for its specific requirements. Above all, this chip gives the possibility of using the 8 channels separately, as a building block of a multichannel system, or combining the internal converters to reach picosecond precision, that could open the way to on-field exploitation of Super Conducting Nanowire Single Photon Detectors (SNSPDs). The chip provides 11 different configurations among which select the best option in terms of a combination of parallel channels, speed and timing precision

Versatile multichannel time-to-amplitude converter for high-speed and high-precision timing applications

Timing measurements triggered by photo-detection are widely used in several different fields, such as Time-Correlated Single Photon Counting (TCSPC), Quantum Key Distribution (QKD) or Light Detection and Ranging (LiDAR) systems. All these applications have in common one essential element, i.e. the timing electronics, which aims at measuring the time interval between two instants and whose requirements strictly depend on the application-specific goal. In this work, we present a versatile and fully-integrated timing chip hosting eight high-performance Time-to-Amplitude Converters (TACs) integrated with a smart logic, providing to the end user a unique flexibility to select the most suitable configuration for its specific requirements