Low Power Smartdust Receiver with Novel Applications and Improvements of an RF Power Harvesting Circuit
Salter, Thomas Steven
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Smartdust is the evolution of wireless sensor networks to cubic centimeter dimensions or less. Smartdust systems have advantages in cost, flexibility, and rapid deployment that make them ideal for many military, medical, and industrial applications. This work addresses the limitations of prior works of research to provide sufficient lifetime and performance for Smartdust sensor networks through the design, fabrication and testing of a novel low power receiver for use in a Smartdust transceiver. Through the novel optimization of a multi-stage LNA design and novel application of a power matched Villard voltage doubler circuit, a 1.0 V, 1.6 mW low power On-Off Key (OOK) receiver operating at 2.2 GHz is fabricated using 0.13 um CMOS technology. To facilitate data transfer in adverse RF propagation environments (1/r^3 loss), the chip receives a 1 Mbps data signal with a sensitivity of -90 dBm while consuming just 1.6 nJ/bit. The receiver operates without the addition of any external passives facilitating its application in Smartdust scale (mm^3) wireless sensor networks. This represents an order of magnitude decrease in power consumption over receiver designs of comparable sensitivity. In an effort to further extend the lifetime of the Smartdust transceiver, RF power harvesting is explored as a power source. The small scale of Smartdust sensor networks poses unique challenges in the design of RF power scavenging systems. To meet these challenges, novel design improvements to an RF power scavenging circuit integrated directly onto CMOS are presented. These improvements include a reduction in the threshold voltage of diode connected MOSFET and sources of circuit parasitics that are unique to integrated circuits. Utilizing these improvements, the voltage necessary to drive Smartdust circuitry (1 V) with a greater than 20% RF to DC conversion efficiency was generated from RF energy levels measured in the environment (66 uW). This represents better than double the RF to DC conversion efficiency of the conventional power matched RF energy harvesting circuit. The circuit is integrated directly onto a 130 nm CMOS process with no external passives and measures only 300 um by 600 um, meeting the strict form factor requirement of Smartdust systems.