Avalanche breakdown protection by adaptive output power control

Cellular phone power amplifier transistors, implemented in low-cost silicon technology, suffer from destructive breakdown. Their breakdown voltage is insufficient to withstand the high collector voltages that occur under extremes. To avoid breakdown an adaptive output power control concept is proposed that makes use of the detected collector peak voltage to limit the output power once a threshold level is crossed. Output power is limited by reducing the effective power control voltage. It avoids opposite actuation of the protection loop and that of the power control loop. For a supply voltage of 5 V and a nominal output power of 2 W no breakdown is observed for a VSWR of 10 over all phases.