Ultralow-Power Optical CDR for Integrated Photovoltaic Energy-Harvesting Sensors

Energy storage elements and electromechanical timing references, such as crystals, can dominate energy-autonomous wireless sensor node volume at the 1-mm³ scale. This brief proposes a clock-data recovery circuit that receives power from integrated photovoltaics and extracts clock and data signals from optical data input. A prototype fabricated in 90-nm CMOS was tested over a V_DD range of 150-500 mV, and it supports maximum data rates from 15 kb/s to 4 Mb/s while dissipating 51 nW-3.5 μW. A software implementation of the conjugate gradient method running on an ultralow-power embedded microcontroller was investigated for its potential to compensate for jitter when the recovered clock is used to sample a sensor input. The output signal-to-noise-and-distortion ratio of an analog-to-digital converter can be improved by up to 16-28 dB for an estimated microcontroller power consumption of 15 μW.