Circuit Design And Implementation For Modem Of UHF RFID Passive Tag

As one of core technology of Internet of Things in the 21 th century, Radio Frequency Identification(RFID), especially passive UHF RFID has the advantage of long identification distance, high reading speed, low cost, and has been widely used in supply chains, logistics, tracing of goods. At present, the way of the maximum energy transmission of passive UHF RFID system and correctly receiving and sending of data have been two main factors restricting the operation distance between reader and tag.This article aims to analysis the principle and way of energy and data transmission, and realization of specific circuits, and must be learn to improving working distance of tag. First, it makes a detailed introduction about the constitution of passive UHF RFID system and the architecture of chip of tag on the whole, it also emphatically analyzes and deduces the principle and way of energy and data transmission, and makes a brief comparison between national military air interface protocol at 900 MHz(abbreviated to “GJB”).With meeting the requirement of the forward communication link in the GJB, it designs two kings of demodulator. The first one has the traits of high sensitivity and low power. It adopts the method of active envelope detection to enhance the sensitivity of demodulator and to reach the sensitivity of 100 mV. With the help of the combination of reference voltage generator circuit and comparator circuit, it can make further efforts to decrease the power and to reach 293.6 nW. The second one has the traits of wide dynamic range and high demodulation depth. It employs native MOSFETs used as a basic envelope transistor in the PDK. The sensitivity of demodulator is reaching up to 150 mV. The designing automatic voltage limitation circuit has better function of voltage limitation in the near field of reader without damaging the envelope signal. The suggestion of average voltage detection makes further efforts to increase the ability of demodulating the low modulation index RF signal for demodulator. The demodulation depth is 10%. In the reverse communication link, the article analyses the influence of the available power and backscattered modulated power of transponder IC in the two kinds of modulation style including ASK(amplitude shift keying) and PSK(phase shift keying). It also designs a kind of low power PSK circuit. With the 80 kb/s data rates, it only consumes 46.3 nW.This article also designs an automatic impedance matching circuit. The RF input power is-13 d Bm, and the rangs of carrier frequency is 860 MHz to 960 MHz, the maximum output voltage of rectifier is maintained to 2.4 V. In the end, the article lists fundamental principles of the design of layout. The chip is fabricated in TSMC 0.18 μm 1P5 M mixed CMOS process. Finally, we carry out simple protocol conformance testing for the tag based on the GJB after packaging.This article explores the principle of energy and data of passive UHF RFID system and proposes specific solution. The designing circuits satisfy the each requirement of GJB.