Design Of Millimeter Wave Broadband Directional Coupler And Mixer

In modern life,the radio frequency transceiver system of wireless communication has been everywhere in people's lives for all aspects.With the development of technology,the frequency band has also developed to the millimeter-wave band,and the research on the ordinary high-frequency band has also become more in-depth.Because of the increasing requirements for the performance of circuits in integrated chips,it is increasingly urgent to optimize the performance of directional couplers and down-conversion mixers that are essential in transceivers.Couplers and down-conversion mixers have become a exploring spot in the industry.At the same time,this research is of great significance for the sustainable development of modern communications.First,the paper summarizes the research progress of directional couplers and down-conversion mixers at home and abroad;meanwhile,introduces and analyzes the process technologies of the circuit in this paper and the structures of passive components such as baluns and inductors.Then,a 45～85GHz broadband coupler circuit using Ga As process is presented in this thesis.The circuit is realized by three symmetrical microstrip lines with staggered branches structure.The branches increase the coupling capacitance and ground capacitance between the microstrip lines in the coupler,which better offsets the influence of parasitic parameters introduced by the discontinuity of the coupler,and compensates the phase speed difference between the odd and even modes of the coupler Isolated signal leakage,then improved the isolation and directivity of the coupler.The three-dimensional electromagnetic field simulation shows that that in the frequency band of 45～85GHz,the return loss of each port of the coupler is less than-26 d B,and the transmission loss of the output port is-0.8d B.The coupling degree of the coupler obtains-9.5d B,the isolation is better than-32 d B,and its directivity is greater than 23 d B.The core structure area of the coupler is 0.31×0.12mm~2,and the area of test structure is 0.74×0.49mm~2.In addition,A 20～30GHz down-conversion mixer based on the 0.18μm CMOS process using the Gilbert structure is designed in this thesis.The mixer uses a transformer balun with better phase performance to realize the differential input of the circuit signal,and uses weak inverse bias technology to make the circuit have lower power consumption.In addition,The output uses a resistance feedback buffer amplifier,which increases the circuit's gain.At the same time,Gilbert's highly balanced structure makes the circuit have better port isolation.The result of simulation shows that when the local oscillator power is-6d Bm,the mixer achieves a flat conversion gain of7.8～9.8d B in the 20～30GHz,and the port isolation is above 27 d B.The circuit operates at a voltage of 1.8V,a quiescent operating current of 10.5m A,and a chip area of 1.41×0.88mm~2.The directional coupler achieves high directivity in a wideband,and the mixer achieves low power consumption and flat conversion gain.It has certain reference significance and application value for the design of circuits in the wireless communication field.