Radio frequency (RF) power-harvesting technology is widely used by the temperature sensors inside high-voltage power-distribution cabinets, which avoids the safety risks caused by the use of batteries. Although the RF electromagnetic wave generated by high-voltage electric fields inside the cabinet can serve as the power supply, it suffers from unstable energy density. As a result, an external device is usually required to power up and read the temperature sensor, such as the near-field communication (NFC) reader of a smartphone. In this case, the RF harvester of the temperature sensor should be sensitive enough to enable a safe operating distance between the external reader and cabinet. Traditional methods combined an AC-DC rectifier and a DC-DC converter to provide a sufficient-high supply voltage for the sensing circuits, but the sensitivity was limited to −21dBm. In this work, an oscillator-enhanced energy-fusion power-harvesting technique is proposed to extend the power-transfer range of NFC. The harvester picks up the NFC energy to start up an oscillator, which enhances the power-harvesting sensitivity of other RF electromagnetic waves such as the 433MHz component in the cabinet. Then, the harvested DC voltage can be increased due to the power superposition of both the 13.56MHz and 433MHz tones. The proposed technique is implemented in a power-harvesting chipset fabricated in 55nm CMOS and 65nm CMOS processes. Measurement results show that the sensitivity of 433MHz power harvester is improved by 4.1dB due to the enhancement of the NFC excited oscillator, which also extends the NFC power-transfer range to 9cm.

Battery-free tags offer a power-efficient solution for the wireless connection in Internet of Things (IoT), where the backscatter communication that is compatible with widely-deployed protocols such as Bluetooth Low Energy (BLE) significantly reduces the hardware cost thanks to the seamless integration into the existing infrastructure. However, there are three main shortcomings in the existing battery-free BLE tags: 1)The tag-to-access point (AP, uplink) communication ranges are limited to 97 meters at -10dBm incident power, which are not long enough for some outdoor scenes. 2) The AP-to-tag (downlink) communication in the state of the arts has not exceeded a 1Mbps data rate and a 4m range, disabling remote tag configuration. 3)The tag-to-tag communication has not been realized in a battery-free way, which cannot construct a passive IoT network. In this work, we demonstrate an integrated bidirectional passive BLE chip that conducts battery-free BLE communication in tag-to-tablet/smartphone, tablet/smartphone-to-tag, and tag-to-tag modes. The chip is implemented in a 65nm CMOS process. An all-digital intermediate frequency (IF) shaping technique is proposed to extend the tag-to-tablet/smartphone (uplink) communication range to 160m at$7.16\mu $W power consumption and a -10dBm incident tone. In addition, a$2^{nd}$-order intermodulation (IM2) based charge-domain GFSK demodulation technique is proposed to enable 1Mbps 12m downlink communication at$6.8\mu $W power consumption, which realizes both tablet/smartphone-to-tag and tag-to-tag communication in a fully battery-free way. As a result, the bidirectional passive BLE chip offers a potential solution for future battery-free IoT mesh network.