Some basic problem about GaN Amp. working in TDD senario.
We all know that when I power on a GaN amp.(usually N -channel depletion type), we need to follow some procedure like below
1) Set VD&VS to 0.
2) Set VG negative enough (like -6V)to deplete the channel inside the MOS.
3) Set the VD to VDQ like 20 volts.
4) Increase VG (to like -2.5V) until ID increase to IDQ like 50mA.
The problem is, if I am doing a TDD. Could I just simply switch the the VG between -2.5V and -6V, or I need to slowly increase VG and observe ID at every transmission time slot starting.
And some more complicate GaN amps. like Doherty with multiple FETs (Driver, Peaker, Carrier).
They have more complex step to power on.
If I use a Doherty GaN amp in TDD. When the Rx time slot is over, could I just simply set the VGs to the same value as last TX time slot I set?
You are correct. The procedure described in the datasheet is more about bring up a device in the lab and is less relevant to operation in the field. So I think that the procedure looks like this.
1. Set Vgg to pinch-off level (say -6V)
2. Set Vd to 20 V
3. Apply RF
4. Pulse Vgg from -6V to -2.5V
5. Wait for duration of transmission
6. Pulse Vgg from -2.5V back down to -6V
8. Pulse Vgg from -6V to -2.5V
9. Wait for duration of transmission
10. Pulse Vgg from -2.5V back down to -6V