| UHF radio frequency identification(UHF RFID) technology is a use of the wireless signal which is coupled to achieve recognition technology. With communications security, without contact, stable performance, etc., it is increasingly being applied to our daily lives.From the system architecture and communication protocol UHF RFID receiver module requires began analysis to determine the performance parameters of the circuit used in the form of a receiver and various modules to optimize its key module.Because of UHF RFID systems require low noise and low power requirements,two mixer circuits are designed, respectively, one-step and two-step frequency conversion architecture. First, the traditional step-conversion as the core, adding cross-coupled dynamic circuits injection structure, and using a capacitive load resistor in parallel to form further filter out high frequency noise, noise figure of the first circuit is only 12.83 d B. Secondly, for the characteristics of high linearity, we designed a two-step conversion mixer circuit,whose input 1-d B compression point up-7.8d Bm.For the next mixer need to use low-noise local oscillator signal, so a LC oscillator circuit is designed. First, we analysis the voltage controlled oscillator works, and combined with the system requirements for the design tradeoff. The eventual adoption of the current bias of the cross-coupled differential LC oscillator, while deduced inductor, fixed capacitors, variable capacitors specific design method to determine the size selection on the basis of negative resistance circuit designed. The output frequency coverage from 1.717 GHz to 1.949GHz; at 100 k Hz, the phase noise is-97.98 d Bc / Hz, when frequency is 1MHz, the phase noise is further reduced to-126.0d Bc / Hz.For the rest of the key circuits used in UHF RFID reader is analyzed, including two frequency divider circuit and the reference current source circuit. First, a simple analysis of the two divider works, and for the critical transistor dimensions were derivated, the simulation results of the second divider circuit. A final design for realizing down-mixer and a voltage controlled oscillator 100μA bias current source, simple structure, in the whole temperature range deviations of only 2.64μA.Through the analysis, design and improvement of the key modules of the reader, such as mixer, oscillator, frequency divider, bias current source, the circuit structure and verification results are given. The circuit structure and the verification results of the two mixer, RFID oscillator, frequency divider and reference current source are presented. |
