A μW Complementary Bridge Rectifier With Near Zero Turn-on Voltage in SOS CMOS for Wireless Power Supplies

An inherent shortcoming of rectifiers designed using standard CMOS devices is poor low input power performance. It is shown that this can be overcome through the use of intrinsic devices with close to zero-threshold voltage available in a 0.25 mu m silicon-on-sapphire (SOS) CMOS process. A novel complementary bridge rectifier structure based on a combination of cross-connected and diode bridge rectifier topologies is introduced to avoid the excessive leakage current incurred through the use of intrinsic devices. A design strategy which maximizes efficiency and produces an input impedance which will interface well with the inductive coil type antennas used in biomedical implants is presented for this new rectifier type. The fabricated rectifier achieves a 1 mu W DC output power for an input power of -26.5 dBm at 100 MHz. A peak measured power conversion efficiency of 67% is achieved at 100 MHz, but more importantly >30% is attained for a wide output power range which reaches as low as -40 dBm. At the target 1 mu W output power a of 44% was achieved.