Joint self-heating and RF large signal characterization

Self-heating affects the RF performance of power transistors and must therefore be characterized for accurate device modeling. This paper presents an active loadpull (ALP) testbed which performs continuous wave measurements with the LSNA for arbitrary loads and substrate temperatures while jointly measuring the device die temperatures with an infrared sensor. Measurements are performed for a 15 W GaN HEMTs for 15, 25, 35 and 45 C substrate temperatures. The thermal resistance is extracted from the dissipated power and temperature data for fundamental loads spanning the entire Smith Chart. The quasi linear relation between the dissipated power and the device temperature increase measured for all loads verifies that a physical temperature is measured. The expected correlation between the dissipated power, output power and device temperature is also evidenced. This ALP testbed provides thus a wealth of joint loadpull, thermal and loadline data which should facilitate the extraction of an electrothermal device model directly from large-signal RF measurements.