3 Sequencing

Powering the PA on and off in a controlled routine is necessary to prevent the V_GS voltage from being too high when the V_DRAIN is applied. Such a state causes the PA to operate in saturation mode which may result in thermal damage in the PA or the board it is mounted on. Powering on a PA requires the following steps:

1. First, apply the V_GS signal to the PA. The V_GS voltage must transition to the V_GS pinch-off voltage or lower. This ensures that when the V_DRAIN voltage is applied, the gate is already low.
2. Next, enable the drain voltage supply and allow the V_DRAIN to be powered to the nominal value (50 V, for example). As the V_GS is at the pinch-off voltage, I_DS must be minimal.
3. After the V_DRAIN is applied, increase the V_GS bias voltage to set the desired power output of the PA.
4. Finally, enable the RF signal. This allows the PA to transmit a signal.

Figure 3-1 GaN Power Sequencing

The PA can be safely shut down by reversing the power-on steps.

1. Disable the RF signal from the PA.
2. Reduce the V_GS voltage to the pinch-off value, eliminating the power output of the PA.
3. Disable the V_DRAIN voltage by sending a disable signal to the drain supply.
4. Finally, the V_GS voltage can be allowed to collapse to ground as the PA is fully disabled.