Sub-threshold CMOS voltage-multipliers using hybrid RF-piezoelectric energy scavenging

We present a novel hybrid voltage-multiplier circuit that can efficiently scavenge energy from a combination of a radio-frequency (RF) signal and a sensor signal which is a low-frequency, low-energy piezoelectric signal from a piezoelectric transducer. The piezoelectric sensor signal is utilized for biasing a cross-coupled differential rectifier chain to an operating point where the RF signal energy can be efficiently harvested even if its amplitude is below the threshold voltage of the cross-coupled rectifier transistors. An adaptive biasing circuit ensures that the optimal operating point of the rectifier/multiplier can be tracked across different levels of input RF signal. The measurement results obtained from a 7-stage hybrid voltage-multiplier operating on 10 MHz RF signals show that the proposed technique can yield significant improvements in power conversion efficiency for low input power as compared to a conventional cross-coupled voltage multiplier circuit on the same die.