Uhf Semi-active Tag Front-end Design

Radio Frequency Identification (RFID) is a fast developing technology, which identify tags without contact. The further development of the internet of things (IoT) and other automatic environment sensing and processing systems, RFID has been enhancing its functions and applications. The technology development drives this enhancement into two directions. The first one is the integration of sensors in the low cost RFID tags. In this direction, semi-passive tags, which have a battery as power supplier, but still use backscatter as the signal transmission scheme, is a newly emerging technology. On the other hand, the increase of applications and data brings about higher security requirement, which drives more security protocol and security circuit design for RFID tags.Firstly, this paper gives analysis of characteristics of the semi-passive tags. Then, it brings about a analog/RF frontend of a semi-passive tag. This paper analyzed the read/write distance, system structure, and life time of the semi-passive tag, and points out that the precise power management is the key measure to prolong the battery life time. Two strategies including the two-stage wake-up circuit and wireless recharge circuit are proposed. The two-stage wake-up circuit makes merits of both low standby power and precise wake-up. The wireless recharge circuit also realized the merits of low recharge power and constant recharge function, comparing with the traditional ones.Secondly, in the semi-passive tag chip, an analog random number generator (RNG) is designed for security applications. Firstly, various kinds of RNG schemes are analyzed and compared. According to the timing, power and area of the UHF RFID, compromises between the bit rate, power consumption and circuit area are made. And two RNG circuits are designed, both of which realized ultra-low power, low voltage, and small chip area.All the circuits mentioned above are taped out in SMIC 0.18μm process with semi-passive RFID tags. Measurement results show that all the power management circuit, wireless recharge circuit realized their functions and the RNGs show good randomicity quality.