Microwave Balun Device Design Based On Integrated Passive Device Technology

Nowadays,with the rapid development of mobile communication technology and the arrival of 5G commercial era,more RF front-end devices need to be integrated in portable terminals.In order to ensure the superior and stable performance of wireless communication systems,higher standards have been set for the miniaturization,performance and cost of devices,which also promotes the industry’s research on integrated passive device(IPD)technology.Balun is an important part of RF passive devices.The study of Balun is of great significance to improve the overall performance of RF microwave systems.Therefore,on the basis of in-depth understanding of thin film IPD process,this paper studied the design of integrated balun on chip based on thin film IPD process.The main work is as follows:Firstly,the lumped parameter Balun design was studied in this paper.In the process of designing lumped parameter balun,four common high and low pass filter models are equivalent to lossless transmission line respectively to realize lumped parameterization of lossless transmission line.Four different combinations of Balun models based on high/low pass filters are discussed,which are T&T type,T&π type,π&T type and π&π type.Based on T&π type structure,this paper introduces a capacitor compensation circuit to further improve the balance of lumped balun.Two frequency transformation factors and two impedance transformation factors are introduced into the ABCD matrix of the high/low pass filter respectively to obtain a lumped parameter circuit model with better performance.Based on the circuit model,the lumped parameter balun of 0.6dB amplitude imbalance and 1.5° phase imbalance in the 2.2～2.9GHz frequency band is finally designed.Different from the lumped parameter balun,in order to cope with the broadband scenario,this paper studied the distributed MarchandBalun design.Based on the improved MarchandBalun,the coupled three-line microstrip line and the improved MarchandBalun are combined,and it replaces the coupled two-line with the coupled three-line,so as to enhance the coupling effect of the coupling line and realize the ultra-wideband.Through theoretical analysis,the Z-parameter matrix model is established.At the same time,the appropriate spiral structure is used to save chips,so that it cannot only be suitable for 5G working band,but also achieve miniaturization design.Finally,the tape test results show that the return loss can reach below 8dB in the passband of 3.0～6.0GHz,the phase imbalance in the band is within ±9°,the amplitude imbalance in the band is within ±0.5dB,the insertion loss in the passband is less than 2.3dB,and the effective area of the chip is only1.2mm×1.5mm。The error analysis is carried out for the measured results and simulation results.Through slicing the chip,it is found that the actual processing results of the width,thickness and spacing of the metal wire are different from the simulation settings.After correcting the error,the simulation results and the measured results are in good agreement,which verifies the correctness of the design theory and provides rich experience for the subsequent film IPD design.