Ambient light interference stands as the primary source of noise encountered by the light detection and ranging (LiDAR) systems based on single-photon avalanche diode (SPAD), which seriously restricts the detection range and accuracy of sensors. Multi-event mode and time-gating method are extensively employed due to their effective suppression ability of the ambient light interference with easily implemented circuit structure. However, the current research on these two operational modes is limited to qualitative description, lacking a comprehensive theoretical analysis. This paper investigates the impact of the multi-event mode and time-gating method on enhancing the imaging capabilities of the sensor, employing a probability distribution perspective. A behavioral model is established, enabling the simulation of the comprehensive functionality of a SPAD-based LiDAR system in either first-hit mode or multi-event mode, including the histogramming, coincident detection, time- gating functions. The model can serve as a substitute for the actual circuit in system function validation and parameter optimization, thereby significantly reducing the design and simulation cycle.

This paper presents a gain-programmable low-noise switched-capacitor circuit for readout of a bulk micromachined gyroscope with a resonance frequency of 3-4 kHz and signal bandwidth of 100 Hz. A charge transfer method is adopted which enables the common node of the sensing and driving structure in gyroscope to a stable biasing voltage, so that the driving force influence of the voltage fluctuation on the common node in the traditional readout method is eliminated. An offset cancellation scheme is used in the readout circuit to suppress the opamp's offset and two programmable capacitor arrays are also implemented on-chip to compensate the initial capacitance offset from the MEMS gyroscope. In order to simulate the transient response of the circuit to the vibrating gyroscope, a simplified model is proposed which uses a time-varying voltage to generate a time-varying capacitor. The chip measures 2times2.5 mm2 in a standard 0.35 mum CMOS process. Simulation results show that the readout circuit can resolve input capacitance variations of 95 aF in 100 Hz bandwidth with 83.4 dB dynamic range from a single 5 V supply.