On the design of unilateral dual-loop feedback low-noise amplifiers with simultaneous noise, impedance, and IIP3 match

This work describes the theory and design of a nonenergetic dual-loop feedback low-noise amplifier (LNA) that provides maximum unilateral gain and simultaneous noise and impedance matching conditions. The dual-loop feedback is implemented in the form of transformer current-feedback and inductive series feedback (emitter degeneration). The current-feedback transformer is also used to neutralize the base-collector capacitance (C-bc), by combining it with a properly dimensioned shunt admittance at the collector output. The result is a single-transistor, unilateral-gain amplifier with high isolation and good stability, eliminating the need for a cascode stage and thus enabeling the use of a lower dc-supply voltage. For the,complete LNA, simple design equations are derived for the unilateralization, noise, and impedance matching requirements. Finally, second-harmonic tuning at the source improves the linearity without compromising the simultaneous noise and impedance match. To verify the presented theory, a 900-MHz hybrid Si BJT LNA has been implemented, which achieves 1.3-dB noise figure, 15-dB gain, - 55 dB isolation, and + 10 dBm IIP3 using a conventional double poly transistor, consuming I-C = 2.5 mA at V-CE = 1.5 V.