Design And Research On GaAs Microwave Switch And Attenuator Circuits

With the rapid development of science and technology,the demonds of communication system by people become stricter.Monolithic microwave integrated circuits(MMIC)meet the people's requirement well because of the improvement of today's semiconductor process.The combination of high cut-off frequency,good consistency,low loss and high output power of MMIC makes it used in citizen communication systems and military facilities extensively.T/R module is one of the most important part of microwave and millimeter wave communication systems.It can be uitilized to receive and transport microwave signal.Switch and digital step attenuator are signal-controlling components in T/R module.Switch controls the “on” and “off” of the road;or it chooses the path of microwave.Digital step attenuator together with digital step phase shifter controls the direction and intensity of active phased array radar systems.It is strategic for active phased array radar and T/R module to research and improve performance of the microwave switch and digital step attenuator.In this paper,the parameters of switch and attenuator in modern communication system will be analyzed.The development and design method will be discussed and presented.This paper will be divided into two parts,one is microwave switch's theory and design,the other is digital step attenuator's.Among the switch part,two kinds of microwave switch will be introduced.And in the attenuator part,a 3-bit digial step attenuator will be discussed.The DC~15 GHz wide band SPDT is based on 0.25 μm GaAs depletion pHEMT process.According to given parameters and combining with theory,the series-shunt topology is selected.By schematic and layout simulation,a DC~15 GHz SPDT is presented.On chip test and assemble test are given to verify the simulation results and make comparision.The final results show the insertion loss is less than 2 dB,isolation is better than 30 dB and input 1 dB compression point is better than 23 dBm.In the second part of microwave switch,a 71~86 GHz high frequency SPDT is presented.To achieve compact insertion loss,an advanced 0.15 μm GaAs enhance pHEMT process is introduced.Artifical transmission line is discussed and uitilized in this design.By optimizing the layout,a 1.2 dB insertion loss with 25 dB isolation and-6 dBm IP1 dB results are achieved.To ensure the reliability,PVT analysis is given.The results show that it is to some extent stable in changing situation.In the attenuator part,a 2~3 GHz 3-bit attenuator is showed.1 dB topology is simplified T structure,2 dB and 4 dB are bridge-T type.Insertion phase shift is mainly discussed and proved by simulation in 8 dB attenuation bit.The final test shows that the insertion loss is less than 1.5 dB,RMS attenuation error is 0.12 dB,insertion phase shift is ±0.5° and IP1 dB is above 24.7 dBm.