Synthesis and Testing of Power Optimized Waveforms (POW) with Focus on 1-POW and Square POW

Abstract

Passive Radio Frequency Identification (RFID) tags are powered by energy-harvesting charge pumps through AC-to-DC rectification of the wireless RF signal: typically a pulse-interval encoded (PIE) continuous-waveform (CW). These charge pumps are comprised of capacitors and diodes, the latter being the leading barrier of passive tag operation. Specifically, the pump diode turn-on voltage is responsible for limited tag sensitivity, read range, and reliability. The Power Optimized Waveform (POW) is a new, non-invasive transmission signal that improves RFID tag sensitivity by providing higher peak voltages without exceeding Federal Communications Commission (FCC) output power regulations. Two POWs that are tested are the 1-POW, comprised of two sinusoids centered about a carrier signal frequency, and the Square POW, the product of a carrier signal and a voltage modulating square wave. A Dickson charge pump was used to measure the power gain of POW versus CW. Spectral efficiency and charge pump efficiency were calculated at different transmit powers and POW frequency spacing. Positive gain was achieved at low transmit powers (< ~4 dBm), and higher frequency spacing, making POW preferable over CW in low power applications.