Gate Voltage dropping under load condition

[MightyBeard7]

We have designed a custom board using the **broken link removed**. We are Using this custom board to provide Biasing voltages to the QPA1022 Amplifier.
We tested the custom board with the following set-ups:-
SETUP-1:- WITH NO LOAD(Power amplifier)
Under this setup Gate voltage is being generated and can be varied by varying VR1(10K pot). VDS is being generated and controlled by TTL input.
SETUP-2:- WITH LOAD(Power amplifier)
Under this setup, the Gate voltage is being dropped to -1.5V, because of this we are unable to set the Drain current but the Drain voltage is being generated.
For the reference find the SETUP-1, SETUP-2 and schematic snapshots..

I am unable to debug the issue. Can somebody help me in this?

SETUP-1


SETUP-2


SCHEMATIC- PAGE1


SCHEMATIC- PAGE2

 

[Carry for cents bazar]

Is your power supply connected to both the gate and drain source? Can it give enough current for both the gate and drain source channel? Check if what is powering the gate can produce the necessary current. For a certain Drain Source current and voltage you need a certain gate current and voltage.

 

[MightyBeard7]

@Carry for cents bazar Thanks for the reply

The biasing/sequence module **broken link removed** needs VGS= -8V hence I am generating -8V from MAX765ESA+(output current 250mA). For VDS(Drain supply voltage) I am feeding externally from RPS(Regulated Power Supply).

 

[FvM]

You should check which voltage is actually dropping first. Can be GCP_IN, -VGS8V0 or VG_A respectively VG_B.

You should also check if excessive current draw of the VGS load is the reason, current can be measured across the 10R series resistor. If so, the most likely reason is a short of in RF circuit, either defective bypass capacitor or GaN FET.

 

[MightyBeard7]

@FvM The IGS(gate supply current) for Power amplifier is 10mA(from datasheet) There is no excessive current drawn from VGS. I need to check which voltage is dropping first

 

[FvM]

I didn't ask for datasheet values but actual circuit health state. Ig is not 10 mA, you are confusing maximum rating with expectable operation current, it's < 1 mA according to datasheet.