Linearized 4-7 GHz LC Tunable Filter with Active Balun in 0.18um SiGe BiCMOS

Abstract

As wireless devices and radar systems become more ubiquitous, there is a growing need for wideband multi-standard RF-SOCs. To enable the advantages of multi-standard systems, reconfigurable RF front ends are needed. Because of the large number of RF signals in wideband systems, tunability and linearity become important parameters. Prior work has shown tunable LC filters to be advantageous in the microwave regime. A balanced-to-unbalanced (balun) transformation circuit is required to support the differential nature of a tunable LC filter. An active balun that also performs as a transconductor to drive the LC tank would relax the design requirement for the LNA and remove a passive balun that would have to precede the LNA. This thesis discusses the linearization of active baluns and presents a comparison between two 4 to 7 GHz tunable BPF designs with active baluns implemented in 0.18 μm SiGe BiCMOS technology. Fourth order filtering is achieved by subtracting two 2nd order LC-tanks. This approach allows 3-dB bandwidth to be tunable from 10% to 20%. In each design, a linearized input active balun is employed to drive the LC-tanks from a single-ended input while preserving noise figure and IIP3 performance. Two different linearization techniques are applied for the balun designs. Simulated NF ranges from 7.5 to 13 dB and IIP3 averages about 5 dBm with the peak value of 21 dBm.