Ruggedness Improvement by Protection

Cellular phone power amplifier transistors have to withstand extreme voltages, temperatures and currents. Requirements on IC and packaging technology are relaxed by using over-voltage and over-temperature protection. To avoid breakdown, protection circuits are used that detect the collector peak voltage and die temperature to limit the output power once a threshold level is crossed. For a supply voltage of 5 V and a nominal output power of 2W, no breakdown is observed for a VSWR of 10 over all phases. For a VSWR of 4 and worst case mismatch phase the maximum die temperature is reduced from 143degC to 112degC when the output power is adaptively reduced from 32.1 dBm to 27.7 dBm