| NFC(Near Field Communication)is more and more widely used in consumer electronics and electronic tags and so on.Typically,it is applied in bus card,metro card,Apple Pay,and Mi Pay.Due to the advantages of fast response,high security and low costs in the NFC,many mobile phone manufacturers are now adopting NFC.The combination of NFC and mobile internet technology brings tremendous demand for mobile payment and promotes the widespread application and rapid development of NFC in the field of global payment.However,there are many kinds of NFC tags circulating in the market with different parameters,various manufacturing technology of mobile phone manufacturers and technical standards,which cause the unfriendly experience of using NFC products.Moreover,NFC involves multiple industrial chains and many hardware vendors,which make NFC technology and related products encountering great challenges in compatibility.As a result,the testing of consistency and compatibility of NFC products by a highly compatible test instrument is imperative before the new products are to be released in future.For now,the development of NFC testing instrument is still blank in the domestic.The relevant test instruments are mainly monopolized by several large foreign' companies and are expensive.Therefore,it is urgent to design a NFC compatibility test instrument with high compatibility,simple operation and reasonable price.These are studied that modulation module,demodulation module,adjustable parameter-setting module and clock extractiohn module.The modulation module and demodulation module ensure the reliability of the test instrument communication.The adjustable parameter-setting module enables the tester to set various physical parameters flexibly in NFC communication,such as carrier frequency,RF field strength,etc.The clock extraction module can generate a new stable signal of the same frequency according to the carrier signal.The signal is for modulation and demodulation module.The main work and innovations of this thesis are as follows:1.The followings are studied,the modulation and demodulation of Type B communication in proximity-coupled devices(PCDs)in ISO/IEC 14443 protocol.The basic modulation function module and demodulation function module are realized in this tester based on the FPGA technology for Type B communication.In the demodulation module,through checking the baseband data,encoding the data in NRZ-L,and adding the header and tail for the data frame and mapping with the waveform,it is achieved that the modulation function for 10%ASK.The response signal of PICC is demodulated by the methods of envelope detection,median measurement and time detection.The accuracy and stability ensure the complete and reliable conmmunication between the smart cards and the NFC tester.2.The testing requirements of the testing instruments for contactless smart cards is studied.In order to be compatible with variable contactless smart cards,the relevant physical parameters of the RF field and waveform parameters of the signal need to be configurable flexibly.The adjustable parameter-setting module can configure parameters flexibly such as baseband data rate,RF field strength,carrier frequency,modulation parameters,the rising and the falling edge time parameters of the signal envelope.The data sent by ARM will be received by FPGA,and then it will be verified and encoded in FPGA.After selecting the sending rate of the baseband data,the design uses load modulation to complete the baseband signal modulation.The modulation module and the adjustable parameter-setting module realize the flexible configuration of the above adjustable parameters.3.A new demodulation method is proposed and implemented based on FPGA for the demodulation function of test instrument.The new demodulation method is more proper than the traditional BPSK demodulation scheme,by means of envelope detection,median decision and time measurement.The envelope detection is achived with the hardware circuit.The mean of the envelope is calculated with FPGA in real time over a period with sliding window.Then,comparing the envelope value with the current mean value,the subcarrier signal is converted to 0 or 1 in binary.The function of time measurement is realized by judging the position of the phase flip according to the result of the median judgment.Finally,the baseband bit stream data can be decoded.4.The requirements of the homo-frequency carrier signal is studied in the test instrument.In addition,a method of generating homo-frequency carrier wave is proposed and implemented.This method of generating the new carrier signal by the frequency meter against the traditional carrier synchronization method.Homo-frequency carrier signals can be generated stably and quickly in a certain frequency range.By this method,stably the homo-frequency signal will be got while there is no carrier signal(or after the carrier signal disappears)on the NFC radio antenna. |
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