A stopband-tunable low-noise differential amplifier with dual-passband and triple-stopband using varactor-tuned bias circuits

A stopband-tunable dual-band low-noise differential amplifier has been developed for the next generation adaptive and/or reconfigurable wireless radios. It employs varactor-tuned bias circuits in the design of low-noise differential amplifiers for suppressing the unwanted signals adjacent to the carrier signals. The amplifier demonstrates dual-passband and triple-stopband performances. Lower, middle and higher stopbands can be independently tuned by varactor-tuned base and collector bias circuits, respectively. With the use of 0.35 µm SiGe HBTs and Si varactor diodes with a capacitance ratio of 2.5, a lower stopband with a maximal gain suppression of 43.7dB for 0.35 to 0.63GHz, a middle stopband with a maximal gain suppression of 25.5dB over 0.61 to 1.17GHz, and a higher stopband with a maximal gain suppression of 27dB across 1 to 2.5GHz have been successfully achieved.