Stability analysis of broadband cascode amplifiers in the presence of inductive parasitic components

Theoretical stability analysis of broadband cascode amplifiers at high frequencies is presented. The stability of the amplifier in the presence of parasitic inductive components is thoroughly investigated. It is shown that the stability can be improved by inserting a series resistance in the gate of common-gate device of the cascode amplifier. To ensure stability, the gate resistance should be selected within specific ranges that are derived analytically. Based on the insights provided by the analyses, several practical design guidelines are given to improve the stability of high-frequency broadband cascode amplifiers. Finally, the derived results are adopted in stabilisation of an X-band cascode amplifier implemented in a 0.18 mu m complementary metal oxide semiconductor process.