M.Sc Thesis

M.Sc StudentSayag Avraham
SubjectHigh Frequency CMOS Low Noise Amplifier Design
Methodology using Slow Wave Transmission Lines
DepartmentDepartment of Electrical and Computer Engineering
Supervisor PROF. Dan Ritter
Full Thesis text - in Hebrew Full thesis text - Hebrew Version


This thesis presents two related topics: a novel design methodology for improving the noise figure of a Ka band LNA (24GHz), and a comprehensive study of slow wave transmission lines that were incorporated in the circuit. The LNA achieved a record low 2.8 dB noise figure, 1 dB lower than state of the art LNA fabricated using the same 0.18 ┬Ám CMOS technology. The obtained noise figure is comparable to the performance of LNAs fabricated using more advanced silicon technologies such as 90 nm CMOS and SiGe heterojunction bipolar transistors. The salient result presented in the section on slow wave transmission lines in this thesis is a new compact analytic model that accurately describes the properties of slow wave transmission lines. The model also provides straight forward physical insight on the principle of operation of slow wave transmission lines.  The essence of the design methodology presented in this thesis is that the transistor current density is determined at an early stage of the design, and transistor gate width only in the last stage. This methodology is based upon the experimental observation that the noise and gain characteristics of the device are primarily determined by the current density. As in most previous studies, we have chosen the inductive source degeneration common source topology, which provides low noise figure and high gain with simple matching networks. The optimal value of the source denegation inductance was determined prior to determining the transistor gate width, for several reasonable gate width values. The insertion loss of the input matching network for different transistor width values was studied, and as mentioned above, only in the last stage the transistor width was determined. The loss of the passive elements in the LNA was reduced using slow wave transmission lines instead of conventional transmission lines or spiral inductors. Slow wave transmission lines exhibit a higher effective dielectric constant than standard transmission lines. Thus, matching elements incorporating slow wave transmission lines are shorter than the equivalent conventional elements, and their loss is significantly lower. Chip size is also reduced by using slow wave transmission lines instead of conventional transmission lines.