Unilateral Power Gain Of Heterojunction Bipolar Transistor

To increase the capacity of Internet,transmission bitrates of 100 Gb/s and 160 Gb/s have received a strong interest.Such applications require electronics based on advanced transistors with cutoff frequencies above 300 GHz.A fundamental property of high-frequency transistors is their maximum oscillation frequency,f_max,defined as the frequency where the device ceases to be active.State-of-the-art transistors offer a maximum operation frequency beyond the capabilities of conventional measurement equipment.So to find f_max,the so called Masons Unilateral Gain is extracted at lower frequencies and extrapolated to the frequency where the gain equals unity,according to the model.Unfortunately,the characteristics of the best high-frequency transistors makes obtained results questionable.A resonance in U-curve occurs,requiring a modified expression for the available power gain when extrapolating for f_max.Mason's Unilateral Gain do not offer a unique solution to the problem,only one that fulfills the definition of f_max.Another expression has been obtained,and experimentally verified,that offer an unambiguous extrapolation.To become creditable,this expression needs also to be theoretically derived.The proposed expression,or a new one,should be confirmed based on Mason's original paper,the definition of S-parameters,and a small-signal model of a transistor.This master thesis describes the whole derivation process of a new available power gain expression(Gp) for the device Heterojunction Bipolar Transistor(HBT's) based on its small signal T-model,with the help of four-terminal network theory.After plotting it,we will see that there is no resonance in maximum available power gain Gp-curve.This means any f_max-value can be extrapolated from a resonant function (U-expression),but extrapolation from Gp-curve brings a well-defined f_max.