DETERMINATION OF MAXIMUM FREQUENCY FOR UNITY POWER TRANSFER RATIO OF HEMTS AND MESFETS FOR HIGH-FREQUENCY APPLICATIONS

Based on the concept proposed for integrated bipolar transistors, the maximum frequency F(pmax) for unity power transfer ratio of a FET amplifier, which is preceded and followed by identical amplifiers, has been determined. An analytical expression for calculating F(pmax) has been derived based on a simplified FET model for the first time. When source and gate parasitic resistances are taken into account, the expression can also be applied to determine the F(pmax) with slight modification. The impact of different circuit elements on F(pmax) of both HEMTs and MESFETs has been investigated and clarified. The calculated results are shown and discussed. The comparison between F(pmax) and f(t) as well as f(max) is made and significant differences between these figures of merit have been observed. F(pmax) is very useful in determining the actual bandwidth of HEMTs and MESFETs for the design of both monolithic and hybrid microwave integrated circuits.