A TEMPERATURE-COMPENSATED CLOSED LOOP OVERDRIVE LEVEL CONTROLLER FOR MICROWAVE SOLID-STATE POWER AMPLIFIERS

摘要

The reliability of GaAs power FETs used in solid-state power amplifiers (SSPA) is adversely affected when operated in an overdrive (excess input power) condition for a long time due to excess gate current. Manufacturers of SSPAs use different schemes to protect the FET power devices from overdrive conditions. One method is to distribute the compression in the device chain; another is to use a limiter circuit. In both cases, however, it is very difficult to fully protect the devices from an overdrive condition, which becomes worse when the SSPAs operate in a varying temperature environment. Some manufacturers also use a feedback control loop for this purpose but its limiting power level is highly sensitive to temperature. A temperature-compensated closed loop overdrive control circuit can eliminate these problems. In this article a detailed description (with mathematical expressions and test results) of a temperature-compensated closed loop overdrive level control (OLC) circuit is presented. This scheme can properly protect the FET power devices from overdrive conditions, irrespective of the change in temperature, and the described mathematical expressions help to design the temperature compensation network without trial and error.