The authors describe a technique for easily calculating normalized determinant function using return ratios. It is shown that an elegant yet simple relationship exists between the return ratios of each dependent source in a linear network and Platzker's normalized determinant function. Using this relationship, the stability (or instability) of linear N-port networks containing any number of active devices can easily be determined using commercially available circuit simulators. An example is shown where this new technique correctly predicts instability in a GaAs MMIC power amplifier. >

A rigorous yet simple method for determining stability of linear N-port networks [and MMIC application]

This paper ties together several different aspects of linear stability analysis as it applies to microwave circuits. In particular, it reviews how the Rollett proviso enters into the well-known stability parameter tests and how the proviso can be evaluated using standard computer-aided-design software.

Rollett Proviso in the Stability of Linear Microwave Circuits&#8212;A Tutorial

The generally accepted method of ascertaining the stability of microwave circuits, i.e. reducing the complicated N-node networks to Two-Ports between input and output, and requiring that K>1 and.

Rigorous determination of the stability of linear n-node circuits from network determinants and the appropriate role of the stability factor K of their reduced two-ports

The authors describe a technique for easily calculating normalized determinant function using return ratios. It is shown that an elegant yet simple relationship exists between the return ratios of each dependent source in a linear network and Platzker's normalized determinant function. Using this relationship, the stability (or instability) of linear N-port networks containing any number of active devices can easily be determined using commercially available circuit simulators. An example is shown where this new technique correctly predicts instability in a GaAs MMIC power amplifier.<<ETX>>

A Rigorous Yet Simple Method For Determining Stability of Linear N-port Networks

The proviso imposed by Rollett [1962] on the well-known stability criteria for linear twoports is examined and redefined as the requirement that at least one set of immittance parameters must have no RHP (right-half plane) poles. It is shown that the proviso can be interpreted as the extreme cases of a newly introduced proviso that requires that the S-parameters defined for at least one pair of arbitrary positive reference impedances have no RHP poles. The new proviso means that the twoport must be stable for at least one pair of arbitrary positive resistance terminations. Since S-parameters are much easier to measure than immittance parameters at microwave frequencies and their direct measurability is an indication of the absence of RHP poles, the new proviso allows us to apply the stability criteria to measured circuits less consciously of the proviso. >

Proviso on the unconditional stability criteria for linear twoport

Many papers and textbooks and the leading CAD (computer-aided design) packages state that a two-port is stable if and only if K>1 and mod Delta /sup s/ mod >

K.T. Hetzler

Papers

Instabilities diagnosis and the role of K in microwave circuits