Analysis of Electrothermal and Impact-Ionization Effects in Bipolar Cascode Amplifiers

This paper is aimed at the analysis of the influence of electrothermal and impact-ionization effects on the dc behavior of bipolar cascode amplifiers. A simple physics-based relationship is derived to predict the limit of the safe operating area in the output diagram. Experiments and circuit simulations are performed on amplifiers in GaAs and SiGe technologies to examine and explain the distortion in the dc
${I}$
–
${V}$
curves induced by these positive-feedback mechanisms, as well as to predict the temperatures of the individual devices.