Modeling of integrated single photon avalanche diodes and design of an ultra-low-power analog readout circuit

Single-photon avalanche diodes (SPADs) are highly sensitive photodetectors capable of detecting light at the photon level. SPADs have a wide range of applications, including biomedical imaging techniques like fluorescence lifetime imaging microscopy (FLIM) or Positron Emission Tomography (PET) scanners. In this context, the ICTEAM (UCLouvain) has developed a thin ultraviolet enhanced backside-illuminated single-photon avalanche diode. The device requires the integration of a dedicated CMOS interface circuit to read and process the signal. The design of the front-end circuitry heavily depends on the characteristics of the photodetector and an equivalent model of the SPAD is often required to facilitate the procedure. Hence, the objective of the thesis is twofold; modeling the SPAD behavior and designing a readout circuit. In the first step, this work proposes a novel compact SPICE model based on TCAD simulations (Silvaco) to accurately reproduce the transient response of the studied SPAD to a light pulse. In the second step, this thesis presents the design of the first stage of the readout electronics. The proposed first amplification stage is achieved by a transimpedance amplifier using a folded-cascode configuration. The design is conducted at the transistor level using the gm/ID methodology. The circuit is simulated and validated at the schematic level using Cadence Virtuoso. It shows a transimpedance gain of 66dBΩ, a bandwidth of 48MHz, and a power consumption of 760µW. It offers similar performance as the state-of-the-art sub-mW transimpedance amplifiers, where the gain is traded for bandwidth.