Balanced-Balanced Tunable Filtering LNA using Evanescent-Mode Resonators

Multifunctional RF components are of great benefit to wireless systems, as they can reduce size and power consumption. A fully balanced Low-Noise Amplifier (LNA), with embedded tunable filtering functionality, using a single transistor, is presented in this paper. The design concept is based on evanescent-mode cavity resonators at the input and the output. The resonators provide filtering, in addition to balanced (BAL) external coupling and a Single-Ended (SE) internal coupling with the core LNA. The internal coupling provides the minimum noise matching to the transistor. A proof-of-concept design is fabricated using a PCB process. The measured results demonstrate a tuning range from 2.8–4 GHz with a noise figure ranging from 3.4–4.6 dB, a balanced gain of 16.7–14.2 dB, and a CMRR of better than 55 dB. The presented BAL-BAL LNA can seamlessly interface with fully balanced RF systems.