Method of designing unit FET cells with unconditional stability

A method of designing unit FET cells for amplification of K-band signals comprising the steps of:

• extracting an equivalent circuit model from S-parameters of a sample device;
• selecting candidate MMIC topologies for said unit FET cell, said candidate topologies including a number of gate fingers and a gate width, the candidate topology for the unit FET cells comprising at least a single drain region between two gate fingers, the two gate fingers being in-between two source regions, the two source regions electrically coupled by an airbridge, the source regions being further electrically coupled by a conductive ground via to an ground plain of an MMIC die;
• determining equivalent linear circuit models for each of said candidate topologies based on said S-parameters, each of said linear circuit models including equivalent airbridge inductance of each airbridge and ground via inductances of each ground via for sources of said unit FET cell;
• changing the number of gate fingers and the gate width to determine candidate topologies with unconditional stability based on said equivalent linear circuit models of each candidate topology
• selecting one of the unconditionally stable candidate topologies based on predicted gain at a frequency of operation in K-band.