An adaptive protection circuit for power amplifier ruggedness improvement

The paper presents a novel protection circuit for power amplifier (PA) ruggedness improvement. This protection circuit is a monolithically integrated, cost and size effective, collector current limiter, indexed to the supply voltage. Compared with conventional protection circuits, the current threshold is indexed to the supply voltage and the protection circuitry uses the same type of device as the RF power transistor to be protected, making it very easy to integrate and more robust to process variations. Moreover, the circuit efficiently protects the PA from all mismatch conditions. The experimental results show that the PA ruggedness is improved (standing wave ratio up to 10:1 for all phases with a supply voltage up to 5.5 V) while maintaining the output power and power-added efficiency under a 50 ohm load.