# A 920-MHz Dual-Mode Receiver with Energy Harvesting for UHF RFID Tag and IoT +
## 1 Introduction  
With the emerging development of the Internet of things (IoT), wireless sensor networks (WSN) are widely used, such as the wearable health monitoring system and environmental monitoring system. Radio frequency identification (RFID) science has the advantages of standardization identification, low cost and small form factor, there is growing interest in combining RFID and on-chip sensors into smart sensor nodes [1; 2; 3; 4; 5]. However, read range is a big challenging topic for these applications.  
The passive RFID tags, whose maximum read rage is limited within 12 m, are powered by the RF energy radiated from the reader [1]. The read range becomes even worse when RFID tags are equipped with sensors [2; 3]. Semi-passive and active RFID tags powered by the external battery; therefore, they are suitable for long read range and sensing. By using the same envelope detector and backscatter topology as the passive tags, the conventional battery-assisted ultra-high-frequency (UHF) RFID tags achieve maximum sensitivity of \(-\)26 dBm and the read range is around 30 m [4]. The receiver is always-on or turned on in each duty cycle. The power consumption of the receiver is several microwatts; hence, the lifetime of the battery is limited.  
In these years, the high-performance transceivers are proposed and implemented in RFID tags to further extend the read range up to over 100 m [5; 6; 7; 8]. However, the heterodyne receiver includes a passive mixer and a local oscillator (LO) which consumes several hundred microwatts power [9]. The lifetime of the tag would be decreased to several weeks. To solve the power consumption issue and avoid the use of LO, the direct envelope detector based receiver (ED-Rx) is a viable technique to scale down the average current and to meet the system power requirement.  
For ED-Rx, there are tradeoffs between power consumption, sensitivity and data rate. In [7], the ED-Rx consumes 1 uW at 930 MHz carrier frequency with a sensitivity of \(-\)55 dBm and a data rate of 10 kbps. However, the high-Q impedance matching technique leads to a narrow frequency band of these receivers, which will increase the design difficulty of the antenna. In addition, these receivers are incompatible with the UHF RFID protocol. When implemented with backscatter circuits and transmitter, the Q factor and passive gain will be decreased, and the sensitivity of the receiver will be decreased to \(-\)30 dBm.  
On the other hand, to break the limitation of the lifetime and eliminate the use of battery, photovoltaic (PV) and thermoelectric (TE) are promising energy sources for RFID tags. For millimeter-sized PV and TE cells, the output power is several microwatts and the output voltage is 0.2 V to 0.4 V in typical. To address these issues, recent efforts have been focused on the fully integrated DC-DC boost converters that can undertake a tiny input voltage (\(V_{IN}\)), while offering a high output voltage (\(V_{OUT}\)) and a high power conversion efficiency (PCE) [10; 11; 12; 13; 14].  
In this study, a dual-mode UHF RFID tag is proposed. The PV and TE energy-harvesting topology is adopted along with RF energy harvesting to eliminate the external battery. The reconfigurable architecture of the receiver is introduced to be compatible with conventional passive RFID tags. The receiver can operate in low-power (LP) and high-sensitivity (HS) modes according to the input signal power. The proposed RFID system achieves low power consumption, long read range and high integration.  
This study is an extended version of our study published in the IEEE 13 th International Conference on ASIC, 2019, Chongqing, China [15]. The chip is taped-out and the measurement results and comparison table are added to this article. The study is organized as follows: Section 2 describes the principle of the proposed RFID system. Sections 3 and 4 shows the circuits and simulation results of energy harvester and receiver. Section 5 is the measurement results. Finally, the conclusion is drawn in Section 6.