Design Of Multi-function Mixer

As is known to all, as one of the important components of RF channel, a mixer has a significant impact on the performance of the whole RF channel. With the development of the RF circuits miniaturization trend, the monolithic microwave integrated circuits(MMIC) have become a research hotspot in recent years. The multi-function mixer circuit in this paper is designed based on the MMIC technology and its working frequency band is 5 ~ 12 GHz.Described in this paper the multi-function mixer circuit mainly has two parts, namely the double balanced mixer and the driving amplifier. The double balanced mixer is a circular double balanced mixer composed of four diodes connected end to end. In the design process of the double balanced mixer, a detailed design process of LO balun and matching circuits is described. Due to the performance of the LO balun have a very important impact on the performance of the entire double-balanced mixer, therefore in the LO balun design process, a detailed analysis of the parameters(turns, wire width, line spacing, OD, ID)effecting the performance of the balun is presented. Finally through the optimization with the simulation software, the balun meets the pre-determined specifications. In the process of matching circuit design, although the common T structure matching circuit is used, we pointed out some problems in the layout of the circuit. Upon the completion of the balun and the matching circuit, the double-balanced mixer is finally and successfully completed after a constant adjustments and optimizations.In the design process of the driving amplifier, the stability of the amplifier is described in detail and the bias circuit and matching circuit of the amplifier are emphatically presented. The guarantee of the stability of an amplifier is very important for any amplifier. Therefore, in this paper, the stability of the amplifier is analyzed in detail and some effective measures to improve the stability of the amplifier are proposed. And due to the dc bias circuit and matching circuit both have influence on the stability of theamplifier, finally, on the basis of a comprehensive consideration of the stability, gain and output power, the amplifier is successfully completed and meets the pre-determined specifications, after several times optimizations and adjustments.Upon the completion of the above two unit circuit, the cascade of two unit circuits is successfully implemented after optimizations and adjustments. Next the circuit is processed and tested and the circuit meets the pre-determined specifications. As much as 43 d B of the LO to RF isolation of the double balanced mixer is superior to the domestic and foreign products of the same frequency band.