Wirelessly Powered Passive Systems With Dynamic Energy Storage Mechanism

Wirelessly powered passive sensors extract the required energy from external radiators. However, their sensitivity is typically worse than -20 dBm due to the limitation of the RF power harvesting. We study the theoretical and practical constraints on the RF power scavenging at low incident power levels. The concept of dynamic energy storage is introduced to enable the operation of the wirelessly powered passive systems at very low input power levels. The extra received power beyond the sensitivity level is stored and later used to enhance the sensitivity of the wireless sensor. As a proof of concept, an integrated wirelessly powered passive transponder with dynamic energy storage mechanism and sensitivity enhancement is designed and fabricated in a 0.13-mu m CMOS technology. Based on the measurement results, the sensitivity of the wireless sensor with matching circuitry has been improved from -18.2 to -27.5 dBm at 900 MHz. The total chip area is 0.8 mm x 0.9 mm.