Research On Broadband And Integrated Balun And Mixer And Applications In Multi-antenna Communication Systems

The 5th generation(5G)mobile communication system has been gradually commercialized since 2019,and a new generation of mobile communication has arrived.The multi-antenna technology with massive multiple-input multiple-output(MIMO)technology as its core plays a vital role and has been highly valued by industry and academia.Multi-antenna communication systems are the development trend of future communication systems.As the communication rate becomes higher and higher,the number of antennas or channels used in multi-antenna communication systems will inevitably increase,which makes the communication system and the corresponding circuit layout more complicated.At the same time,since communication systems and measurement systems need to support as many communication standards as possible in many cases,their operating frequency ranges need to cover multiple frequency bands.Therefore,under the premise of ensuring communication quality,the multi-antenna communication system puts forward higher requirements in terms of broadband,integration,and miniaturization,which is of great significance to conduct in-depth research on it.This dissertation major in the key technologies and research hotspots of the RF receiving front-end of multi-antenna communication systems,and conducts in-depth theoretical research on key devices and system integration,as well as verification by experiments.The major innovation achievements are listed as follows:(1)In this dissertation,the passive double-balanced monolithic integrated mixer with Marchand baluns is studied in depth,and a method of developing a wideband mixer is proposed.Firstly,by further studying the characteristics of ideal Marchand balun,the relationship between its operating bandwidth and characteristic impedances is obtained,and a research method based on deviation impedance is proposed,which is beneficial to better observe the impact of the change in characteristics impedances of the coupled transmission line on the bandwidth of Marchand balun,laying the foundation for subsequent mixer design.Secondly,the harmonic balance method is adopted to simulate and observe the input impedance characteristics of the diode core of the mixer driven by a certain power of the local oscillator signal as the size of the diode changes.Then,combined with the impedance characteristics of the Marchand balun,the appropriate size of the diode is determined.The advantage of this design process is to make full use of the RF characteristics of the Marchand balun and the diode core to obtain good matching between stages,making the design of the mixer more compact and fully reducing the introduction of redundant circuits,which is beneficial to obtain a wide operation frequency range,as well as reduce the chip size.The mixer is fabricated in WIN's 150 nm Ga As p HEMT(pseudomorphic High Electron Mobility Transistor)process.The measurement and simulation agree well,exhibiting an operation frequency range covering from 7 up to 40 GHz,with more than 30-d B isolation from LO port to RF port.The above research results have been published in Wiley International Journal of RF and Microwave Computer-Aided Engineering.(2)A novel compact broadband balun with operation frequency range of more than a decade octaves is proposed,which break through the limitation of traditional Marchand baluns with operation frequency range of mostly a few octaves.The novel balun is comprised of two parallel spiral coupled transmission lines.The equivalent coupled line model reveals that its amplitude imbalance of the balun with symmetric structure equals to the coupling coefficient of the coupled line in decibel.It is known that spiral structure based coupled transmission line has very high coupling degree of close to 1(i.e.0 d B),which is suitable for use in baluns,and on this basis,it is only necessary to slightly adjust the size or layout of one side to slightly change its coupling degree so as to achieve an excellent property of amplitude balance and obtain the needed balun with good performance.Accordingly,two novel wideband baluns with different coupling methods are designed and fully simulated by electromagnetic simulation software.One balun is based on edge-coupled spiral transmission lines,which is fabricated in WIN's IP2M(Integrated Passive 2 Metal)process of owning two metal layers.Measurement shows that the balun has the operation frequency range covering from 2 up to 18 GHz(Fractional Bandwidth,i.e.FBW,160%),with insertion loss of less than6 d B,amplitude imbalance of less than 1 d B,phase imbalance of less than 3 degrees and reflection coefficient of less than-10 d B.These research results have been published in IET Electronics Letters.The other balun is based on broadside-coupled spiral transmission lines,which is fabricated in Sanan's IPD(Integrated Passive Device)process of owning three metal layers.Measurement shows that the balun has the operation frequency range covering from1.34 up to 16.37 GHz(Fractional Bandwidth,i.e.FBW,170%),with insertion loss of less than 8 d B,amplitude imbalance of less than 0.67 d B,phase imbalance of less than 5 degrees and reflection coefficient of less than-11.8 d B.These research results have been published in IET Electronics Letters.(3)Deep research is conducted on the integration and miniaturization technology of multi-channel RF receiving front-end with broadband operation frequency range,and two multi-channel RF receiving front end systems of owning dual-or four-channel are developed,which has the operation frequency range covering from 0.2 up to 6 GHz and support a switchable signal bandwidth between 40 MHz or 80 MHz.Each receiving channel in the systems adopts a secondary-frequency-conversion super-heterodyne structure and its intermediate frequency is determined by the center frequency of the surface acoustic wave(SAW)filter,which can be flexibly set in the frequency range of 50 up to 200 MHz.Based on the system indicators and the placement of off-chip devices such as filters and frequency synthesizers,and fully considering the factors such as signal flow and the relative positions of the chips' ports,a single channel is divided into multiple key components according to the top-down design method.Each key component is realized by a specific multi-function chip,which is composed of several unit circuits such as broadband low noise amplifier(LNA),mixer,gain block,RF switch,digital attenuator,positive-negative voltage level converter and so on,and fabricated in WIN's 150 nm low noise p HEMT process.After fabrication,the dual-channel system is builded by bonding bare chips to printed circuit board(PCB).As for four-channel case,the system must be builded in the PCB board with the same area.Thus,the method via bonding bare chips to PCB board is no longer applicable.A new method is using LTCC process to package bare chips and parts of filters into a single-channel RF receiving system-in-package(SIP),which is efficient and economical.Parts of this research result have been published in Journal of Microwaves and accepted by Microwave Journal.