Direct Monitoring of RF Overstress in High-Power Transistors and Amplifiers

Light emission from power transistors at a compression level in the range of 2-3 dB has been imaged using a microscope-mounted camera. Results show that the emitted light intensity distribution across the transistor is highly nonuniform and depends on the load impedance, direct current, and RF conditions. The light intensity correlates with a negative gate current, which is a result of the RF-induced impact ionization in the transistors. The nonuniformity in the light intensity is attributed to the RF-induced voltage overstress in the transistors. The observed light emission may be used as a direct and contactless monitor of the RF-induced overstress in transistors and power amplifiers