The Design And Realization Of Universial Transceiver Front-end Based On AD9361

With the rapid development of wireless communication technology,RF front end as the core component of wireless communication system is responsible for the conversion between RF signal and baseband signal,its performance affects the indicator of the entire communication system.With the improvement of wireless communication requirements in various fields,Requirements for RF front-end features turns to multichannel,long-distance,wide band,omnidirectional communication.Based on the practical topic,this paper aims to design a dual-channel general transceiver RF front end based on AD9361.The operating frequency range of the two channels is not less than 200 MHz.When using omnidirectional antenna and IF bandwidth is not greater than 4MHz,this dual-channel general transceiver RF front end can reach 1km communication distance.In this paper,based on the AD9361 transceiver chip,the addition of low noise amplifier ensures that the receiver spurious dynamic range based on the improved receiver sensitivity,the addition of power amplifier improves the transmit power of the transmitter,and to ensure that the third-order intermodulation of the transmitter is not less than 30 dBc.The Balun circuit was designed between the AD9361 and the amplifier and the smallest system was established for the AD9361.The main design work of this paper is as follows:1.According to the circuit structure and the transmission distance,Spurious-free dynamic range and third-order intermodulation of the transceiver,the key indexes of 433 MHz,1.65 GHz receiver and transmitter channel are analyzed and calculated respectively,And put forward the requirements of the indicators of Balun circuit,low noise amplifier chip,amplifier chip,matching circuit.2.In 1.65 GHz low noise amolifier,matching circuit were designed according to both optimum noise match and mismatch looses,the low noise amplifier with a noise figure of 1.56 dB and a mismatch loss of 0.12 dB is implemented.A decoupling circuit of the power supply is designed according to the target impedance required by the receiver when the minimum signal is input,Increases the sensitivity of the 1.65 GHz receiver to-90.5d Bm / 4MHz and reduces the overall noise figure to 2.5dB.3.The maximum output power of the 433 MHz and 1.65 GHz transmitters is set at 25.7dBm and 23.95 dBm respectively in the amplifier circuit from the output signal of 1dB compression point,third-order intermodulation coefficient,matching loss,and power amplifier output and gain.Using the maximum power transmission matching,the maximum quiescent current operating point set the way to ensure the output power of the power amplifier,and using partial decoupling to prevent the power fluctuations of the power amplifier on the operating point of interference,and to ensure a stable operating point.4.According to the relative bandwidth and loss required by 433 MHz amplifier matching,the maximum Q value of each node is calculated.By controlling the Q value control,the multi-element matching method is used to realize the input impedance in the range of 6.2 + j * 4.6?,Matching to 50 ohms near the 200 MHz range make the return loss is not less than 15 dB,the broadband match of 433 MHz amplifier is achieved.5.According to the impedance characteristic of 1.65 GHz amplifier,the impedance at the center frequency is close to 50 ohms,the impedance change per unit bandwidth is relatively larger,the parallel LC resonant circuit is used to bend the impedance,increase the matching bandwidth,and complete the 1.65 GHz power amplifier Broadband match.6.According to the RF PCB design criteria from the plate selection,cascade design,RF signal integrity,power supply,ground and several key issues in front-end PCB were designed.7.The test of the RF front end of the general transceiver based on the AD9361 is completed,including the matching test,the gain test,the receiver dynamic range test,the transmitter third-order intermodulation coefficient test,1km long distance communication test.The test results meet the requirements of the functional indicators,verify the feasibility of the design.