Small Signal Amplifier Design: A Collection from Applied Microwave & Wireless

Inductive Emitter Degeneration

The process of intentionally inserting additional inductance between device emitter connections and RF ground is a common method used for influencing device input/output match, noise match, stability and linearity. Inductive degeneration does not impact noise figure performance as seriously as resistive degeneration does. In this design, two microstriplines, each with dimensions of 0.15 mm 1.9 mm, serve as inductors between each device emitter lead and PCB ground plane. This additional inductance provides series-series negative feedback, improving amplifier third-order intercept and gain compression points, at the cost of reduced gain. For this LNA, approximately 1.5 to 2 dB of gain is traded to attain improved linearity. In other words, typical gain in a similar applications board with direct emitter grounding was 16 to 16.5 dB. This gain was reduced to 14.7 dB by using inductive emitter degeneration.

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