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This paper presents an RF energy harvester embedded in a low-power transceiver (TRX) front-end. Both the harvester and the TRX use the same antenna and operate at the same frequency of 2.4 GHz. To decouple the harvester from the TRX, different concepts are proposed regarding the transmitter (TX) and receiver (RX). To avoid loading the TX, the harvester is decoupled with an nMOS switch that can be enabled with a start-up rectifier. Concerning the RX, the decoupling mechanism relies on the nonlinear input impedance of the main RF-DC converter. The harvester also includes a supply management circuit for over-voltage protection and charging energy storage devices with a constant current or voltage. The energy harvester has been co-integrated with the low power TRX in a 130 nm CMOS process and achieves a measured peak power conversion efficiency of 15.9%. For input power levels of at least -9 dBm, it is able to charge up a supply capacitor to a regulated voltage of 1.34 V. The impact of the harvester on the TRX performance is measured with respect to an identical TRX front-end without harvester, showing little impact on the TRX performance. Both TX output power and RX noise figure are degraded by less than 0.5 dB. As an additional feature, the start-up rectifier is also used for demodulation of On-Off-Keying (OOK) signaling, which can be used as a secondary wake-up channel. Since the required area for the harvester is only 0.019 mm2 (≈ 2% of the total active TRX area), it can be added to the TRX at almost no cost.
Date of Publication: July 2013