Title :
A 1-GHz active phase shifter with a ferroelectric varactor
Author :
Mahmud, Ali ; Kalkur, T.S. ; Jamil, Asad ; Cramer, Nicholas
Author_Institution :
Dept. of Electr. & Comput. Eng., Colorado Univ., Colorado Springs, CO, USA
fDate :
5/1/2006 12:00:00 AM
Abstract :
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 nonideal 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 I GHz when using a BST capacitor with a tunability of 2.75:1.
Keywords :
active networks; barium compounds; bipolar transistors; circuit tuning; ferroelectric capacitors; microwave phase shifters; strontium compounds; titanium compounds; varactors; 1 GHz; 200 to 1100 MHz; BST varactor; Ba0.5Sr0.5TiO3; active phase shifter; all-pass response; bipolar junction transistors; control voltage; feedback network; ferroelectric varactor; high-Q tuning element; nonideal transistors; parallel plate capacitor; passive phase shifters; transfer function; Binary search trees; Bipolar transistor circuits; Capacitors; Circuit optimization; Dielectrics; Feedback circuits; Ferroelectric materials; Phase shifters; Strontium; Varactors; Active circuits; ferroelectric capacitors; phase shifters; tunable circuits and devices;
Journal_Title :
Microwave and Wireless Components Letters, IEEE
DOI :
10.1109/LMWC.2006.873529