Stability of high-frequency transistor in common-emitter configuration

This letter describes the stability of the common-emitter transistor in terms of the y parameters in the high-frequency range; the graphical representation of the normalised input admittance of the transistor is also shown. This representation is useful and convenient for investigating performance of the input admittance in both design and analysis of circuits. The maximum frequency of potential instability of the common-emitter transistor is established using an approximate high-frequency equivalent circuit of a junction transistor.