A 0.3 lx-1.4 Mlx Monolithic Silicon Nanowire Light-to-Digital Converter With Temperature-Independent Offset Cancellation

Abstract

This article presents a monolithic light-to-digital converter (LDC) based on silicon nanowires. The silicon nanowires are arranged in a configuration, which allows cancellation for the offset due to dark leakage current and facilitates system-level chopping of the signal chain, including the nanowires. The readout integrated circuit (ROIC) has an analog front end (AFE) with a resistive-feedback transimpedance amplifier (TIA) to provide a constant voltage that strongly biases the nanowires. A programmable-gain switched-capacitor incremental delta-sigma analog-to-digital converter doubles the output of the TIA and feeds a digital back end that provides a decimated output. Finally, system-level chopping reduces the residual offset and 1/f noise, and 50-/60-Hz rejection suppresses interference from mains lighting. Fabricated in a 0.18-mu m CMOS process, the LDC has an input-referred current noise density of 235 fA/root Hz, and a dynamic range of 106.7, from 0.3 lx to 1.4 Mlx. The offset from the nanowires and the AFE is reduced to less than 30 mu V and offset drift of 193 nV/degrees C in a temperature range of -40 degrees C-85 degrees C. The AFE of the LDC draws 59.5 mu A at 3.3 V, and the digital back end draws 8 mu A at 1.8 V.