Accuracy of Broadband On-Wafer Load Pull Measurements

Numerous systems are currently available for taking semi-automated load pull measurements. The majority of these systems use computer controlled, passive microwave tuners. At Texas Instruments a test set has been constructed around one of these systems to make broadband on-wafer measurements on large numbers of devices. Through various experiments, the accuracy of the system is examined both at the tuner and on wafer reference plane, and errors discussed. The calculation of a normalized VSWR is introduced as a useful method to quantify measurement error, and other means of quantifying error are also discussed. The result is a test set capable of accurate on-wafer measurements from 6-18GHz at high reflection coefficients. These capabilities make possible not only the broadband characterization of devices without lengthy calibrations, but also the ability to measure larger devices without specially dedicated prematched devices, which use up valuable wafer space.