Junction temperature dependence of high-frequency noise in heterojunction bipolar transistors

The use of the Hawkins model, under isothermal condition, to calculate the bias dependent high frequency noise in Heterojunction Bipolar Transistors (HBTs) is questioned. The inclusion of thermal effects into the noise model of HBTs is necessary as the temperature of the device becomes progressively different from the ambient temperature with increasing bias current. Calculation of noise figure by including the thermal effects explains the experimental measurement whereas the isothermal calculation underestimates the noise figure at high bias current.