Electrothermal Effects on Performance of GaAs HBT Power Amplifier During Power Versus Time (PVT) Variation at GSM/DCS Bands
Power versus time (PVT) variation is one of the most important features for describing electrothermal performance of RF power amplifiers (PAs) for global system for mobile communication/digital cellular system bands. The PA sometimes produces high power at the first time slot and low power at the second time slot, which results in similar temperature variation caused by its self-heating effect. Therefore, both theoretical and experimental investigations are carried out for capturing electrothermal effects on the performance of GaAs-based heterojunction bipolar transistor (HBT) PAs. The temperature distribution over the PA die is obtained using our in-house developed finite-element method algorithm and a thermal infrared scanner, respectively. In particular, the PVT variation of the PA for a two time slot, as well as a four time slot (i.e., 75% of its operation time is in the “power on” state) case is studied in detail. Furthermore, an improved design for the GaAs HBT PA chip is performed, fabricated, and tested with its PVT variation suppressed effectively. This study should be very useful for the development of PAs for many wireless communications.