1310/1550 nm Optical Receivers With Schottky Photodiode in Bulk CMOS

Abstract

This article presents optical receivers in bulk CMOS technology with integrated Schottky photodiodes (PDs). These PDs can detect photons with an energy below the silicon bandgap, such as the 1310/1550 nm wavelengths typically used in single-mode fiber applications. In particular, a comparison of Schottky PDs in 28 and 40 nm bulk CMOS and its circuit design implications are given. As these PDs have a relatively low responsivity, however, a low-noise electronic front end is required to convert the low photocurrents into voltages suitable for signal processing. Positive capacitive feedback and designing near critical damping are two techniques that can improve the noise performance of transimpedance amplifiers. These techniques are thoroughly analyzed and demonstrated. Finally, measurement results of silicon implementations with integrated Schottky PD using these techniques are presented.