Hi,
I’m experiencing an issue with the discrete transistor QPD0030. After approximately one and a half days of continuous transmission at a nominal output power of around 41.5 dBm, I’ve observed a gradual degradation in gain. With the same input power, the output power begins to drop—initially by a few dB, eventually falling significantly below the nominal level.
In some cases, restarting the unit temporarily restores the output power to nominal levels, but it drops again after a few minutes. If transmission continues, the transistor eventually becomes permanently damaged. When this occurs, the drain current rises to over 1 A, and either a gate-to-source junction short develops or there is an issue with the drain-to-source junction. During normal operation, the current typically ranges between 600–670 mA, depending on the transmission frequency. The dissipated power is approximately 20 W.
To improve thermal management, our pcb has extra copper layer inside the vias beneath the transistor. A heatsink is permanently exposed to airflow, and the board temperature appears stable after a few minutes of operation. As a driver, I’m using the QPA9419, preceded by a variable attenuator stage as shown in the block diagram. The RF section is isolated from the rest of the circuitry and enclosed in its own box, with the top wall positioned 3.07 mm above the transistor.
I also measured the case temperature of the QPD0030 and recorded 153°C on the top of the package.
I would be grateful for any advice or recommendations to help identify the root cause of this issue and how to resolve it.
Thanks,
Ondrej Kucera
