Research On Radio Frequency Identification Analog Front End Based On Metal Oxide TFT

Radio Frequency Identification(RFID)is a kind of technology that can achieve information interaction between a reader and an electronic tag through a radio frequency signal.RFID is indispensable for the development of the Internet of Things.With the concept of the Internet of Everything proposed,the application of RFID is more promising.Compared with amorphous silicon TFT(a-Si TFT)and polysilicon TFT(poly-Si TFT),Metal oxide thin film transistor(MOTFT)have many advantages such as simple production process,low cost,high field effect mobility,etc.So it is often utilized in the design of driver circuit and pixel circuit of panel displays field.Using MOTFT to design electronic tags can realize low cost,flexibility and transparency of electronic tags,which can further promote the development of flexible wearable devices and makes a great difference to relative research field.Firstly,this paper introduces the main circuit modules of analog front-end of electronic tag,and then using MOTFT to design rectifier circuit,modulation and demodulation and charge pump circuit according to the electrical characteristics of MOTFT under the top gate technology.Moreover,the design ideas of clock extraction circuit,reset circuit and voltage limiting circuit are also discussed.A full-N rectifier circuit is designed by using MOTFT.The test results show that the output DC voltage changes from 0.8 V to 7 V,when the input signal is 1 MHz and its voltage amplitude changes from 4 V to 14 V.The output DC voltage changes from 0.8 V to 6 V,When the input signal is 5 MHz and its voltage amplitude changes from 4 V to 14 V.It shows that the output of the rectifier circuit is less than that of 1 MHz when the input signal is 5 MHz.By adding an auxiliary circuit to the traditional ASK demodulation circuit,the simulation results show that the proposed circuit improves the falling speed of the envelope signal edge.We test the ASK demodulation circuit.The test results show that the demodulated signal high level is 1.44 V at 5 V operating voltage when the carrier is frequency of 1 MHz,the amplitude of 5 V and the data modulation rate of 2 kbps.The demodulated signal high level is 1.51 V at 5 V operating voltage when the carrier is frequency of 2 MHz,the amplitude of 5 V and the data modulation rate of 1 kbps.Under the two different test conditions,the edge of output waveform decreases and rises slowly.We conclude that it may be due to the excessive parasitic capacitance of the actual circuit,leading to the deviation of time constant from the design value.The resistance load modulation circuit is designed and the simulation results is showed.The traditional fourphase clock charge pump circuit output stage is improved.By adding two extra transistors and two capacitors,the threshold voltage loss caused by diode connection in the output stage is eliminated.The simulation results show that the output of improved four-phase clock charge pump increases about 1 V compared with that of the traditional at the input voltage of 5 V and the clock frequency of 100 kHz.Finally,the design ideas of clock extraction circuit,reset circuit and voltage limiting circuit are discussed in detail.The design and implementation of each circuit module in this paper lay a foundation for the the subsequent design of electronic tags integrated by TFT.