Ultra-low-voltage circuits for sensor applications powered by free-space optics

Ultra-low-voltage circuits powered and clocked by free-space optical links are implemented in 90 nm digital CMOS. A CDR circuit powered by 4.6 klx illuminance recovers optical data at 50 kb/s using interleaved subthreshold oscillators. A passive-filter ¿¿M produces a 47 dB peak SNDR at 2.1 klx and 256 kHz sample rate. The CDR consumes 217 nW at 300 mV V_DD and 200 kb/s. The ¿¿M consumes 102 nW at 400 mV V_DD and 1.6 MHz for a figure-of-merit of 23 fJ/conversion-step.