Preferably an "external supply", e.g. an inverting DC/DC converter powered by the 28V input or an existing auxilary supply in your amplifier circuit. You need to make sure that the negative bias powers up before the drain voltage.
I think you realized that's it's no reasonable option to bias a flanged microwave transistor by a source resistor.
Sir, if i make a simple calculation, Vg= Vgs - Vs.
Vg ( which if i used a fixed bias configuration, would be [R2/R2+R1]*Vdd] )
And Vs would be Id*Rs ( i asume Id is equal to Is ).
Then if we just say that we want Vgs become -1.7, then -1.7v= Vg + Vs ( we should think that if we add Vg with Vs, the result should be -1.7v ).
And that made me confuse sir, because a source resistor would have been a 'part' also in biasing ( based on the calculation Vgs= Vg + Vs ).
I've never used a GaN HEMT as an amplifier before, i normally used BJT transistor and worked in low power and low frequency, so that the biased voltage would depend also on the emitter resistance ( source in BJT ) [ Vbase=Vbe+Vemitter ].
And my second question sir, why would we use DC/DC converter that supply a negative bias ( e.g. cuk converter with buck regulator ), why don't we use just a normal fixed bias configuration that gives -1.7V rather than use a converter DC/DC ?
I just wondered.
Thank you very much for your help sir,i really appreciate.
( I'm sorry if i looked too big headed, because when i learned about analog device, my lecturer said that if we want to bias a class A amplifier using BJT or FET, the best and the 'normal'
way is using Fixed bias as the configuration like the pictures below ).