High-efficiency integrated readout circuit for single photon avalanche diode arrays in fluorescence lifetime imaging

Abstract

In recent years, lifetime measurements by means of the Time Correlated Single Photon Counting (TCSPC) technique have led to a significant breakthrough in medical and biological fields. Unfortunately, the many advantages of TCSPC-based approaches come along with the major drawback of a relatively long acquisition time. The exploitation of multiple channels in parallel could in principle mitigate this issue, and at the same time it opens the way to a multi-parameter analysis of the optical signals, e.g., as a function of wavelength or spatial coordinates. The TCSPC multichannel solutions proposed so far, though, suffer from a tradeoff between number of channels and performance, and the overall measurement speed has not been increased according to the number of channels, thus reducing the advantages of having a multichannel system. In this paper, we present a novel readout architecture for bi-dimensional, high-density Single Photon Avalanche Diode (SPAD) arrays, specifically designed to maximize the throughput of the whole system and able to guarantee an efficient use of resources. The core of the system is a routing logic that can provide a dynamic connection between a large number of SPAD detectors and a much lower number of high-performance acquisition channels. A key feature of our smart router is its ability to guarantee high efficiency under any operating condition.

Full Waveform LiDAR for Adverse Weather Conditions

“…If using a focal plane array, there are limited space and thermal budgets, and if we increase the complexity of the data storage (e.g. for full histograms instead of single points), then we reduce the fill factor and the frame rate accordingly [93]. Simple binary logic and external frame summation can reduce the frame time (to as low as 10 ms [94]) but that does not allow full wave data analysis of the type described in Section IV.…”

High-accuracy and video-rate lifetime extraction from time correlated single photon counting data on a graphical processing unit

“…To overcome this tradeoff, a new approach has been proposed at Politecnico di Milano, which exploits different technologies for the various parts of the system, each one specifically selected to optimize a single aspect of the problem. 20 The system targets the use of custom-technology SPAD detectors, which have been proven to provide best-in-class performance in terms of a combination of PDE, noise, and detector jitter. 21 These detectors require dedicated electronics developed on purpose to attain the best performance, and in fact, in the past few years several dedicated circuits have been presented in the literature, [22][23][24] paving the way to the development of such a high-performance, densely integrated TCSPC system.…”

“…Moving from this consideration, the camera under development at Politecnico di Milano has been designed starting from the data rate that can be reasonably handled by the currently available technology: a target throughput of 10 Gbit/s. Such an amount of data will be generated exploiting five conversion circuits 20 along with 10 bits to address the 32 × 32 detector array pixels. The exploitation of only five conversion circuits shared with a 32 × 32 detector array poses tight constraints on the resource sharing mechanisms to avoid distortions and inefficiencies.…”

A CMOS SPAD Imager with Collision Detection and 128 Dynamically Reallocating TDCs for Single-Photon Counting and 3D Time-of-Flight Imaging

“…Since the detected photons have to be read off-chip for processing, the IO bandwidth determines the maximum photon throughput, so as the number of the photons that can be read out in each cycle. In this case, a per-pixel TDC architecture exhibits low efficiency in both power consumption and area occupancy, due to the sparse photon detection [ 13 ]. To improve the fill factor, instead of a per-pixel TDC architecture, a TDC sharing scheme is employed in this design.…”

“…In fact, due to the digitization of photons, a large volume of data can be generated then read off-chip via bandwidth limited IOs. In most situations, instead of the TDC number, the IO bandwidth is the major limitation to the photon throughput [ 5 , 8 , 11 , 12 , 13 ]. Therefore, to avoid the distortion due to photon pileup, the pixel activity must be restricted to 1–3%.…”