Threshold Voltage Compensated RF-DC Power Converters in a 40 nm CMOS Technology

Circuit techniques termed as threshold voltage (Vth) compensation are utilized for CMOS RF-DC power converters or more specifically RF charge pumps to improve the power conversion efficiency at low levels of RF input voltage. In this work, we present two differential RF charge pumps for UHF RFID transponder ICs that include a Vth compensation. The first circuit uses gate biasing for Vth compensation, whereas the second circuit design follows a combined approach of gate and bulk biasing. The circuits have been manufactured in a 40nm low-power CMOS technology. Measurement results demonstrate that the power conversion efficiency can be improved from 39% to 42% at a given output power of 4µW and an output voltage of 1V by using bulk biasing. Both circuits show a low input quality factor of 13 at this output power level and allow therefore the implementation of highly sensitive broadband UHF RFID transponders.

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