A dual-band SiGe HBT active load using stacked LC resonators and RC series feedback circuits

A dual-band SiGe HBT active load is presented for use in the reflection type phase shifter with a wide phase-shifting range and low insertion losses. The active load is based on a common-emitter configuration of SiGe HBTs employing stacked LC resonators in the load circuit for a wide shifting-range at multiple frequencies as well as RC series feedback circuits between emitter and ground for improving return losses. Since the parallel LC resonators with different resonant frequencies are stacked in configuration, the individual resonant frequency can be varied independently. The implemented dual-band active load using 0.35 μm SiGe HBTs with an ft of 25 GHz and Si varactor diodes with a capacitance ratio of 2.5:1 has achieved a maximal phase shift and a return loss of 270° and 0.6 dB at 0.64 GHz as well as 300o and 1.9 dB at 0.87 GHz, respectively.