| Phase shifters are used in a variety of applications, including communications and radar, as well as in on-chip applications such as clock recovery circuits. Both active and passive phase shifters have been widely studied. Active circuits mostly rely on solid-state devices for tuning while passive phase shifters often use a ferroelectric or micro-electro-mechanical system (MEMS) device. This research pursues the novel idea of using a ferroelectric varactor in an active circuit. The superior characteristics of such a device are combined with the advantages of an active system. This thesis dissertation presents an overview of competing technologies along with a brief discussion of the characteristics of ferroelectric varactors. The design, implementation, and analysis, along with measured results, are also covered for the completed system.; An active phase shifter circuit implemented with discrete components is reported. The tuning element, a ferroelectric varactor, is a parallel plate capacitor with Ba0.5Sr0.5TiO3 (BST) as the dielectric. The circuit consists of two bipolar junction transistors coupled with a feedback network, which contains the varactor and thus produces a transfer function that can be varied with a control voltage. The active nature of the circuit allows for signal gain, while the BST varactor provides a high-Q tuning element. This represents an improvement over strictly passive phase shifters with ferroelectric elements. Circuit simulation results are presented and compared with measured data from the implemented system. The network, even with markedly non-ideal transistors, can provide a true all-pass response over the frequency band of interest (200-1100 MHz). The measurement results demonstrate an analog tunability of about 100° with a gain variation of about 0.6 dB at 1 GHz when using a BST capacitor with a tunability of 2.75:1. |
