In general, for a linear two-port device characterized by S-parameters, the two necessary and sufficient conditions to guarantee unconditional stability (e.g., no possibility of oscillation when the input and output of the device are both terminated in any passive real impedance) are

a) K>1, and (b) ?<1, where

An alternative form for these two conditions as

a) K>1 and b) B ₁>0, where

can be found in the literature [2].

A simulation tool is of great help when trying to optimize an amplifier for stability. The Ansoft Serenade design environment was used for simulations in this LNA design, including evaluating the stability factors K and B ₁ up to 6 GHz.