On A Chip Integrated Optimization Design Of Spiral Transformer And Balance

As the market demands of consumer electronics such as the wireless communication, radio frequency identification and mobile TV etc. are rapidly growing, miniaturization, high performance, low cost and power consumption are more and more important. As a consequence, SOC (System On a Chip) has attracted more attention and interests. However, the lack of high-quality passive devices has become a bottleneck in the RF or microwave system.On-chip passive devices, especially monolithic transformer and balun (balance to unbalance), arevery important for improving the performance of circuit or system, and they become more crucial when supply voltage is getting lower. Balun is indispensable in the transformation between single-ended and differential circuits. Due to the loss characteristics of Si substrate and complexity as well as numerous parasitic effects of passive devices, it is still a big challenge to implement high performance monolithic transformers and baluns.In this thesis, monolithic transformer and balun are discussed and studied based on the process of IBM7wl. The analysis is made according to the influence on the performance index caused by different geometric design parameters. The3D EM simulation software is HFSS, which is produced by Ansoft. First, coplanar transformer with turn ratio1:1is studied. It reveals how the geometric design parameters affect the performance of transformer. Then stack transformer is discussed. Merit and demerit of different structure of stack transformer is concluded according to simulation and a higher performance transformer is designed with lower insert loss and high self resonance frequency using the conclusion discussed above. Finally the method to implement a high performance balun is discussed, using the conclusion obtained from the research of monolithic transformer and a stack balun with good balance and low insert loss is achieved. An optimization method, namely, wider centre tap, is also discussed, which can improve the performance of balun effectively.