A Research Of Integrated Miniaturized Mixer

In order to accommodate signals having a wide percentage frequency bandwidth, facilitate upconversion ahead of higher frequency receivers and improve sensitivity of receivers, researchers have developed a high performance passive mixer that allows original equipment manufacturers to optimize receiver design. Such mixers are of great use in both military and civilian applications. The most primitive single-ended and single balanced passive diode mixers gradually get abandoned due to poor isolation and low IF output frequency. Following balanced mixer are widely favored cause its wider operating bandwidth of the RF and LO signals, higher isolation, large input third order intercept point IP3 and so on, but there are disadvantages such as commly-6 d B or even bigger insertion loss and about 10 d Bm local oscillator power. Circuit structures of active mixers are complicated and size get way big when taking microstrip line as transmission line especially in microwave band, which is not in favor of integrating and quite on the contrary of miniaturization. Therefore, there are still undefeated strumbling blocks in the research of miniaturized passive devices in microwave communications.This thesis starts with research background and significance of miniaturized mixers, followed by introduction of history, status and prospect, then explains the working principle of mixers in detail, analyzes concepts and calculation methods of various performance parameter of mixer. After that theoretical research of planar balun is given and verified through simulation. On this basis multilayer Marchand balun is introduced and its performances are verified also through simulation to realize miniaturization.After a comprehensive comparison between different structures of mixers, we choose double balanced structure to implement the mixer this paper presents. Diode chip HSMS2827 of Avago is taken as diode ring. Module is established in ADS software using SPICE parameters. Characteristics of impedance with frequency for RF, LO circuits are simulated to provide initial value for impedance matching. Various performance parameters of multilayer Marchand balun are analyzed and modules are built in three dimensional high frequency electromagnetic simulation software HFSS based on LTCC technology. Cascade balun is selected to design the mixer after comparision. RF, IF and LO balun are optimized through simulation. SNP files exported are joined with diode model in cascaded simulation to ensure the performance of miniaturized broadband mixer.This paper presents the design flow of a double balanced mixer detailedly, cascaded balun is adapted to broaden bandwidth and a IF balun is added to improve isolation. Finally the implenmented mixer is tested. The mixer designed has a operating bandwidth of 3-7 GHz for local oscillator and Radio Frequency, DC-2 GHz for IF, within bandwidth 3-7 GHz conversion loss is between-10 to-6 d B, third-order intercept point IP3 is more than 10 d Bm, isolation between LO port to the RF port is bigger than 35 d B while that between LO port to IF port more than 13 d B. In summary, the double balanced mixer this paper presents meets requirements for engineering applications due to its broad frequency bandwidth as well as high isolation.