Design Of Hardware Circuit Of UHF RFID Reader

Radio frequency identification(RFID) is a non-contact automatic identification technology, which has been developed rapidly in recent years. HF RFID technology has been very mature,however,UHF RFID has great development space and will become mainstream. UHF RFID has many advantages such as disposable read multiple tags, long identification distance, fast data transferring speed, high reliability and so on. On this basis, this paper has designed a low power consumption, small size RFID reader hardware circuit which works at UHF band.According to the requirement of the paper, AS3991 RFID reader chip produced by Austriamicrosystems is chosen as the core part of the circuit. The size of the chip is only 9 x 9mm, and there are two output power modes: 0d Bm and 20 d Bm. 20 d Bm output is used in this paper, with the internal integrated power amplifier, which not only guaranteed performance of the reader but also reduced the circuit size. Then the power supply circuit, loop filter circuit and the oscillator circuit of the RFID reader chip are designed. According to the requirements of the design, suitable low pass filter, Balun and the directional coupler are selected. C8051F340 microcontroller is used in digital control part. Then USB circuit, reset circuit, as well as the chip connection with AS3991 has been designed. The reader uses the USB power supply and C2 pin for downloading and debug. For RF chip outputs differential signals, The differential outputs need to be converted to singleended outputs in order to pass the low pass filter. This is done by a Balun. So a matching circuit between AS3991 and Balun is designed using ADS. To further realize the miniaturization, the matching circuit used Low-temperature co-fired ceramic(LTCC) technology, which reduced the size of circuit by about 30%.The circuit schematic diagram is designed in Altium Designer. After selecting chips and devices, Printed Circuit Board(PCB) layout is designed. Then we make the UHF RFID Reader. The final step is testing the circuit board. In normal power supply mode, we test the frequency of voltage pin supplied to the chip, chip in the standby state of the output waveform, and the normal work of the output power and the operating frequency to verify it can work.