Research On High Linearity Low Noise Amplifier Employing Dual Active Bias Technique Based On SiGe Technology

Recently, with the increase of wireless users and throughput of data flow, transmission technologies with higher spectrum efficiency are required so as to provide higher quality services within the limited extent of spectrum for more users, which inevitably require higher linear RF front-end. As the first active module stage of a wireless receiver, the linearity of Low Noise Amplifier (LNA) has a direct influence on the linear performance of the whole system. Thus, the research on high linearity LNA becomes one of hot topics in RFIC field domestically and overseas. With the rapid development of SiGe technology, SiGe BiCMOS technology has been widely used in RF front-end circuit. In this dissertation, the main factors which impact on the linear performance of SiGe HBT are investigated by an analytical method. Then, an improved dual-active biasing structure is proposed to improve the linearity of SiGe HBT. Finally, the new biasing structure is applied to the design of high linear SiGe HBT broadband LNA, and then the LNA layout is given.First, based on the Gummel-Poon model, Volterra-series analysis was performed to obtain an insight into the linearity behavior of SiGe HBT. Volterra-series analysis indicates that there exists mutual cancellation mechanism for nonlinearity among the four major factors, namely gm, Cdiff, CBC and RB, making the SiGe HBT good linear characteristics. The further analysis shows that a stable bias operating point is important for improving the linear performance of SiGe HBT.Secondly, in order to stabilize the bias operating point, hence improve the linearity of SiGe LNA, an improved dual-active bias structure is presented. The stabilizing effect on the LNA bias operating point by the improved dual-active bias structure is studied in mathematical method. The effectiveness of the bias structure is verified by Agilent RF design software ADS (Advanced Design System).Thirdly, based on this improved dual-active bias structure, a1.5-5.5GHz high linearity broadband SiGe HBT LNA is designed. Taking the gain, noise figure and linearity into account, the cascode structure with good reverse isolation is selected in the LNA topology. LC impedance matching technology is utilized to accomplish the input and output ports impedance matching. And then, frequency extension technologies such as shunt peaking technology and emitter parallel capacitor feedback are employed to compensate the gain reducing in high frequency, thus, the gain flatness is improved.Finally, the performance of the LNA is simulated by ADS. The results show that, in the frequency range from1.5to5.5GHz, the LNA has an Input3rd order Intercept Point (IIP3) between2.2to5dBm, the maximum improvement amplitude of IIP3is14.2dBm compared to the LNA with traditional passive bias in the same topology, which verifies effectiveness of the novel dual-active bias structure in improving the linearity of the LNA. Simultaneously, the LNA has a gain (S21) of22.5dB, a noise figure below3.5dB, and the input and output reflections (S11and S22) less than-10dB over the bandwidth range from1.5to5.5GHz. Meanwhile, the LNA is unconditional stable. The overall results exhibit that the LNA has good performance. At last, the RFIC layout design rules and geometry optimization methods are disscussed, and the layout of the high linearity and broadband SiGe HBT LNA with the improved dual-active bias structure is designed based on JAZZ0.35μm SiGe BiCMOS technology.