Research On Mixer And Amplifier Multifunction Chip Of L-band Based On Gaas Technology

With the wide application of active phased array technology in modern radar and communication systems,the cost,area and power consumption of phased array systems are required to be higher and higher.Traditional phased array components are composed of discrete devices,which have many problems such as large circuit area,high cost,poor consistency and complex assembly,etc.The multifunctional chip in this study integrates multiple functional subsystems in an integrated way,which makes up for the disadvantages of traditional phased array components and is of great significance for the development of phased array systems.Based on GaAs pHEMT process,this study designed two multifunctional chips work-ing in L-band,and focused on the research and analysis of key units in the circuit.The specific work content is as follows:（1）Aiming at the problem of large insertion loss and large area of traditional passive mixer,this paper modeling analysis on the balun converter,add a tail capacitance on the balun end,which reduces the electric length of the balun transmission line,and applies it to the passive dual-balanced mixer to improve the frequency conversion loss of the mixer.Based on this structure,a down converter with RF frequency of 0.96-1.25GHz and local frequency of 1.31GHz is designed.The final design result is:the frequency conversion loss is less than 9dB,the output P_1dBis greater than 3.9dBm,and the isolation degree from the local oscillator to the intermediate frequency terminal is greater than 38dB.（2）In order to solve the problem that the noise and gain characteristics of LNA cannot be taken into consideration at the same time,the degenerate negative feedback structure of source pole is introduced to establish the relationship with the input impedance,and the optimal matching point is selected to realize the noise and gain characteristics of the circuit at the same time.In order to solve the problem that the gain of wideband amplifier rolls down with frequency,the RC negative feedback structure equivalent model is estab-lished to compensate the transistor gain rolls down and realize the high gain flatness of the circuit in wideband.A low noise amplifier is designed based on this kind of topological structure.The simulation results show that,in the range of 0.96-1.25GHz,the amplifier gain is greater than 31dB,the noise coefficient is less than 0.8dB,and the gain flatness is less than±0.5dB.（3）In view of the contradiction between the traditional switch isolation and insertion loss characteristics,this study adopted the series and parallel structure then combined with the equivalent model of pHEMT switching devices to analyze,designed a single-pole double-throw switch with high isolation and low insertion loss characteristics.Simulation results show that:within 0.96-1.25GHz,the insertion loss of the switch is less than 0.33dB,the isolation degree is greater than 52dB,and the output P_1dBis greater than 18.8dBm.