Research And Design Of Broadband Mixer

The rapid development of wireless communication has made communication more convenient,but compact equipment and complex communication standards also put forward higher requirements on the bandwidth of the RF front-ends.As an important part of the receiver chain,the performance of the mixer has also received a lot of attention.And using a wideband mixer in the RF system can avoid the multi-branch design of the mixing channel,reducing the complexity of the system design and the chip size compared with the narrowband mixer.In response to this,the thesis first introduces the significance and function of mixers in receiver,and conducts extensive research on broadband mixer technology,so as to determine the appropriate technical route for specific project requirements.Then,the general working principle and main performance indicators of the mixer are introduced,and the main topology structure of the mixer is described in detail.Next,the general foundation and common topology structure of baluns are introduced,so as to be selected in different scenarios.Finally,to meet the demand for wideband mixers in civil and military fields,a broadband down-conversion mixer is designed with Ga As technology.The mixer takes the passive double-balanced structure as the core to perform the mixing operation of the radio frequency signal and the local oscillator signal.The bandwidth of the passive mixer is mainly limited by the RF balun,and the active balun is easy to achieve the wide bandwidth.However,there is still a large local oscillator signal fed into a single RF port even for double-balanced topology,so that the transistors of active balun are pre-saturated,which in turn limits the overall linearity.In order to increase bandwidth without suppressing the linearity of the passive mixer,the Ruthoff structure is used to design the passive balun in the thesis.The designed Ruthoff balun has a three-inductor configuration,in which the two inductors are spirally wound in parallel to form a coupled line balun,and the third inductor is used for auxiliary adjustment of phase and amplitude balance.In addition,in order to compensate the conversion loss of the passive mixer and reduce the local oscillator injection power,the intermediate frequency output buffer and the local oscillator input buffer have been designed successively,which both adopt a distributed topology,and each single stage adopts a cascode amplifier to achieve broadband and high reverse isolation.By reasonable layout planning and iterative optimization,the post-simulation results show that the designed mixer RF covers 4.5 to 18 GHz,IF covers 0.8 to 4.5GHz,the gain range is from-0.5 to 2 d B,and the fluctuation is 2.5 d B;the single sideband noise is from10 to 13 d B;1d B input compression point is from-1 to 2.8 d Bm.The overall performance meets and exceeds the requirements.