20W Output Broadband Amplifier with Automatic Gain Control and Thermal Protection

Abstract

The requirement is to explore concept, design, fabrication and testing of a common source class B, cwrf amplifier by using readily available MOSFET that can withstand a load mismatch at all phase angles with more than a VSWR of 20:1. This amplifier must give an output of more than 20W with 13dB gain in the frequency range of 28 to 46MHz i.e. 37 ± 9MHz. This module will make one of the stages for a multistage cascaded high power cwrf solid state amplifier. The amplifier must be over current and over voltage protected by using external self-regulated dc power supply at the drain. The amplifier MOSFET device is presently to be biased at the gate with a variable dc supply. This arrangement will make it gain controlled. This will be feed backed from the cwrf output so as to make it automatic gain controlled in future. Various techniques of sampling forward and reflected power at the output must also be explored. A thermoswitch at the heat sink of MOSFET is to be added along with necessary circuitry to regulate the operating temperature, thereby protecting the device from overheating.