This book focuses on ultra-sensitive PIN and avalanche photodiode receiver (USPAR) ICs for data communication. After more than 20 years of exploitation of the pin-photodiode CMOS technology leading to efficient APD and SPAD receivers and sensors, this book describes how ultra-sensitive PIN photodiode receivers close the loop back to PIN photodiode ICs. In contrast to conventional optical receivers, which are based on resistive-feedback transimpedance amplifiers (TIAs), the book uses charge integration on small photodiodes with a low capacitance known from image sensors to reduce the noise considerably – even better sensitivity than with SPAD receivers is achieved. To obtain a much larger light sensitive area as in pixels of image sensors, innovative low-capacitance pin-finger and dot photodiodes are introduced. Important advantages of USPAR ICs are much lower circuit complexity, much smaller chip area and much lower power consumption as of SPAD receivers. In addition, error correction can be avoided. Detailed investigations of photodetectors and integrating amplifiers with many surprises and astonishing results of newest research will be described. Key Features: Describes newest research results in the field Covers basics to applications Includes properties of USPAR receivers compared to that of SPAD receivers in compact form. Explains dedicated ultra-low-noise circuits to exploit charge-integrating receivers in detail. Presents microelectronics and optoelectronics combined in an easily understandable way. Included numerous elaborate illustrations and tables facilitate and enhance comprehension.