DESIGN, MODELING AND CHARACTERIZATION OF AN ACTIVE PHASE SHIFTER USING A FERROELECTRIC CAPACITOR
Ali Mahmud, T. S. Kalkur, Asad Jamil, N. Cramer · Integrated ferroelectrics · 2006
This paper reports an active phase shifter circuit implemented with discrete components and which uses a ferroelectric capacitor as the tuning element. The circuit consists of two bipolar transistors coupled with a feedback network that has a voltage variable transfer function. The active nature of the circuit allows for signal gain, while the ferroelectric varactor provides a high-Q tuning element. Thus, the overall performance is improved by the advantages of both technologies. Computer simulations with measured results from the implemented system are presented and show that the network, even with markedly non-ideal transistors, can provide a true all-pass response over the frequency band of interest (100–500 MHz). The measurement results demonstrate an analog tunability of about 140° with a gain variation of about 1 dB at 300 MHz when using a Ba0.5Sr0.5TiO3 (BST) capacitor with a tunability of 2:1.