Characterisation of power transistors for wireless network applications using passive and active load-pull

Power transistors are important devices in the transmit chains of wireless communication networks. In this paper, two methods are discussed for the characterisation of power transistors namely passive and active load-pull. The load impedance at the output of the transistor is swept over a region of the Smith chart to find the load conditions which optimize various characteristics of the transistor which are critical for the overall effectiveness and efficiency of the wireless network. In passive load-pull, the load impedance is controlled using a mechanical tuner whereas in active load-pull it is controlled by signal injection. Results obtained from applying the two methods to the testing of a Gallium Nitride (GaN) power transistor are discussed in detail at several frequencies.