|M.Sc Student||Segev Gal|
|Subject||Study and Design of CMOS Phase Shifter|
|Department||Department of Electrical Engineering||Supervisor||Professor Emeritus Yael Nemirovsky|
|Full Thesis text|
The phase shifter is a component where the phase difference between its input and output is controlled electrically, mechanically or magnetically. Phase swing, phase resolution, insertion loss, amplitude deviation and chip area are some of the characteristics which define the quality of such a device.
A phased array antenna system is the most robust application of such a component, providing the ability to steer its beam in space, without mechanically shifting the antenna. Both civil and military radar systems are examples of applications which extensively use this component.
In this thesis we present design and characterization of a phase shifter based on RC bridge topology on the 0.18µm RF-CMOS process commercially available in Israel. Traditionally, the approach consisted of using a tunable capacitor to obtain the phase shift. The suggested work consists of both tunable capacitor - varactor - and tunable resistor - transistor - therefore providing more design flexibility. Additionally, voltage control nodes were implemented in order to offer the ability to fine-tune the device post-fabrication, thus to slightly reduce the phase error due to process variation.
The proposed phase shifter consists of 5 bits, full phase swing coverage design, having a resolution of 11.25º and 1GHz bandwidth on a central frequency of 12.5GHz. The circuit itself is fully differential and consists of 4 basic phase shifting units, each responsible for a different shift. Also, five amplifiers are used to match the input and output to 100Ω and also to act as isolating buffers between each of the basic phase shifting units. Two sub-circuits of the main design were fabricated and characterized in order to assess the performance of the suggested topology. In addition, extensive research in terms of EM simulations regarding the behavior of the process coils was performed.
Temperature stabilization techniques were also extensively investigated in this work. Two stabilization sub-circuits were designed and fabricated in IBM 0.18µm process to support the amplifier losses as a result of temperature dependent effects.