Research On PCD Digital Demodulation Algorithm Based On ISO/IEC 14443 Protocol

The contactless IC card system is composed of a proximity card(PICC)and a proximity coupled device(PCD),which complete information transmission through wireless communication.However,the PCD demodulation error is large and the speed is slow,which will lead to the problem that the system cannot communicate correctly.The improvement of demodulation ability can not only play the performance advantage of PICC chip,but also improve its reliability and security,which plays a key role in the operation of the system.Therefore,in order to ensure the normal operation of the system and the stability and security of communication,it is necessary to improve the demodulation algorithm to reduce the demodulation error,improve the demodulation effect,and improve the demodulation efficiency.According to the engineering requirements,this paper takes a certain PCD chip as the research object and studies the implementation of on-off Keying(OOK)andBinary Phase Shift Keying(BPSK)demodulation algorithms.The carrier synchronization and symbol synchronization in OOK non-coherent demodulation andBPSK coherent demodulation are analyzed and optimized in detail.The specific work content is as follows:1.In order to solve the problem that the demodulation circuit design is too simple in the communication process between the chip and TypeA card,and demodulation in counting mode leads to poor demodulation effect and unable to communicate normally,an incoherent demodulation algorithm based on Hilbert transform is studied.Firstly,the principle and implementation method of non-coherent demodulation are studied;then,the Hilbert transform is introduced in the envelope extraction process of incoherent demodulation,which simplifies the hardware circuit design;finally,the feasibility of the algorithm is verified by simulation,the advantages and disadvantages of the algorithm and coherent demodulation are compared,and the demodulation scheme is determined.2.Aiming at the problem that the frequency offset occurs during the communication between the chip and the TypeB card,the difficulty in synchronizing the carrier lock leads to large demodulation errors and communication errors.a carrier synchronization algorithm based on Hilbert phase detection is proposed;aiming at the problems of large amount of code element synchronization operation,resulting in slow demodulation rate and slow communication,a code element synchronization algorithm with increased interpolation points is proposed.Firstly,the principle and implementation of carrier synchronization and symbol synchronization in BPSK coherent demodulation are studied;secondly,the original algorithm was optimized by replacing the traditional Costas loop phase detection with Hilbert phase detection,which effectively corrected the carrier frequency offset and added Gardner timing synchronization loop interpolation points to speed up the determination of the best sampling time;finally,the feasibility of the proposed carrier synchronization and symbol synchronization algorithm is verified by simulation,and compared with the traditional algorithm.The simulation results show that the proposed algorithm can effectively correct the carrier frequency offset,preserve the signal characteristics,reduce the computation amount of symbol synchronization loop,speed up its locking speed,and improve the efficiency of understanding modulation and accuracy.3.The hardware design and verification of the proposed algorithm are carried out.Firstly,the top-down design method is adopted,and the RTL-level function verification of the algorithm is verified by the joint simulation of Matlab,Quartus II.and Modelsim;then,the Field Programmable Gate Array(FPGA)development board was used to build the test platform,complete the prototype verification of the demodulation algorithm,and collate the data,compared with the original algorithm,Under the condition of the same packet loss rate,the required signal-to-noise ratio environment is reduced by 11 dB and the performance is significantly improved;finally,the DC synthesis tool is used to realize the conversion of RTL code to gate netlist based on SMIC 0.13μm process,and the integrated demodulation algorithm circuit achieves a balance between area,timing and power consumption.