Design and Implementation of Silicon-Based Distributed Amplifiers

As the demands for broadband communication continue to expand, the development of high-speed data link has attracted great attention recently. With the requirement of operating bandwidth, the distributed amplifier is the most widely used topology to overcome the limitation of gain-bandwidth product. In the choice of process technology, compound semiconductors such as GaAs or InP are preferable due to the superior high-speed characteristics of the transistors Unfortunately, these processes have higher cost and are not suitable of chip system integration. The recent advance in CMOS and BiCMOS process technologies motivates the study of silicon-based optoelectronic integrated circuits due to the lower cost and higher level of system integration. Therefore, the circuit implementation of Si-based distributed amplifier is chosen as the topic of this thesis.

In the design of distributed amplifiers, the inductors or transmission lines are required to construct the signal propagation paths at input and output. The inherently low quality factors of the passive components have long impeded the implementation of Si-based distributed amplifiers. In this thesis, the characteristics of the passive components have been studied and modeled for the optimization of the distributed amplifiers.

From theoretical analysis, the gain-bandwidth product of distributed amplifiers with conventional architecture has been limited by the fmax of active devices. In a CMOS technology large parasitic capacitance in gate and drain terminal of active devices leads to a smaller bandwidth while the low transconductance imposes strict restrictions on the overall gain of the distributed amplifiers. On the other hand, the large equivalent parasitic impedance at the base of bipolar devices degrades the circuit performance in a BiCMOS technology. In order to alleviate the design issues, a CMOS folded distributed amplifier is first proposed to optimize the bandwidth. It exhibits a power gain of 5±1.15dB within the frequency range from 6GHz to 32.5GHz. In the second design, another CMOS distributed amplifier is designed for high power gain. The simulated gain and bandwidth are 9±0.9 dB and 3.3GHz, respectively. Finally, effort has been made for the design of a SiGe HBT matrix distributed amplifier using emitter degeneration and self-bias technique, achieving a gain of 9.5±0.5 dB and a bandwidth of 49GHz.