Photodiodes: Electronics and Noise Analysis

This lecture covers the electronics and noise characteristics of photodiodes. It begins with the equivalent circuit of a photodiode, detailing components such as the current generator, dark current, junction capacitance, and series resistance. The instructor explains various measurement circuits, including a simple measurement circuit with a load resistor and a transimpedance configuration that utilizes an operational amplifier. The lecture also discusses integration circuits for current-to-voltage conversion, emphasizing the importance of reset and integration processes in photodiode applications. The cutoff frequencies and speed limitations of photodiodes are examined, highlighting the effects of diffusion and drift times. Noise sources are analyzed, including photonic noise, dark current noise, and thermal noise, along with their impact on performance. The dynamic range of photodiodes is discussed, noting the influence of load resistance and saturation effects. The lecture concludes with a summary of key characteristics, such as quantum efficiency, noise factors, and compatibility with CMOS technology, relevant for applications in imaging systems.