Evaluation of thermal balancing techniques in InGaP/GaAs HBT power arrays for wireless handset power amplifiers

Three layout-based techniques designed to equalize the temperature distribution in GaAs HBT output arrays of Power Amplifiers (PAs) are evaluated. Electrothermal simulation results show that a reduction in the range of 4–5% of the peak of the junction temperature rise over ambient can be achieved with a negligible increase in design complexity and area, and that up to 7% can be obtained by further optimizing the distribution of base ballast resistors. This is a positive outcome in regards to long-term device reliability since the probability of a failure is reduced when the highest junction temperature in the array is decreased. However, and extensive experimental characterization of PAs incorporating the array variants reveals that the temperature reductions are too low to yield quantifiable improvements in RF performance and ruggedness.