AN1232 Datasheet, PDF (1/6 Pages) STMicroelectronics – Ruggedness improvement of RF DMOS devices

AN1232
Application note
Ruggedness improvement
of RF DMOS devices
Introduction
RF amplifiers often experience impedance mismatch between output and load. Such an
impedance mismatch generates a reflected wave towards the RF power transistor, making a
much more stringent working environment for the transistor. Working conditions grow critical
when the load is disconnected from the output of the RF power transistor, since, in this case,
the reflected wave amplitude becomes comparable to the incident one.
RF transistors are able to withstand severe impedance mismatch conditions particularly
essential for applications such as plasma generators or nuclear magnetic resonators which
operate under rough conditions. DMOS devices used in such applications appeared to lack
the necessary ruggedness when operating under severe RF load mismatch conditions. This
weakness was believed to be intrinsic.
Based on the need to improve the ruggedness of RF power DMOS, an investigation was
carried out and a theoretical model simulating the failure mode mechanism was developed.
Finally, relevant corrective actions were undertaken.
July 2007
Rev 13
1/6
www.st.com