A Comparison of APD- and SPAD-Based Receivers for Visible Light Communications

Visible light communications is an alternative method of indoor wireless communications that requires sensitive receivers. Ideally, single photon avalanche detectors (SPADs) could be used to create more sensitive receivers. However, the dead time, finite output pulse width, and photon detection efficiency of existing SPAD arrays limit their sensitivity and bandwidth. In this paper, an accurate equation for the impact of dead time on the sensitivity of a SPAD array is presented. In addition, the impact of the width of the output pulses on the
on–off
keying data rate is investigated. Finally, a comparison between receivers containing an avalanche photo-diode (APD) and a large array of SPADs shows that although the receiver containing the SPAD is more sensitive in the dark, the APD-based receiver is more sensitive in a normal operating condition. However, the models that predict the performance of both receivers suggest that newer SPAD arrays will enable significant improvements in receiver sensitivity.