A novel, fully automated, fully calibrated multiple-stimulus measurement system has been developed for the extensive characterisation of complex amplifier structures under single-tone and modulated signal excitation. Achieving precise relative phase and magnitude control of the independent RF, base-band and bias signals allows analysis and measurement of otherwise hidden device interaction. Use of the measurement system in characterising multiple-device amplifier behaviour has led directly to a novel optimisation approach, allowing the efficiency and linearity to be maximised. In order to control the base-band impedance environment, a fully calibrated IF-load-pull capability has been incorporated, allowing investigations into amplifier sensitivity to memory effects, specifically those associated with base-band impedance termination. The features of this system are demonstrated through its application in characterising a dual input Doherty structure. By varying a number of independent parameters including relative RF input phase, relative RF input power and bias, behaviour has been uncovered that has led to improved insight and understanding of the Doherty structure.
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