I'm system engineer, so don't know well about PHEMT or HEMT chip.
I'd like to use HMC598 and HMC-ALH382, HMC-ALH476 like doubler or AMP.
These chips are required some bias sequence.
You can find PDF file about bias
//Design and Implementation of a Bias Sequencing Circuit for the HMC463LP5 Low Noise Amplifier//
that circuit is method how to make proper bais sequence.
They say VGG should be turned on than VDD. I understood it and It did good.
But, when VGG is turned off, is it okay?
I think VDD will be turnd off after VGG. It may be problems.
But that application note notice only tuned off speed by using VDD' capacitor.
Now, I want to know correct bias sequence.
Could I ignore bias when chips are turnd off?
I'm going to move this into the RF forum where someone should be able to help answer this question. I did find another article which might be useful as well.
I already check that PDF file. In my case, I use standard amplifier bias sequence and cascode distriuted amplifier bias sequence.
But they focused only turn on time without turn off time.
Generally, the biasing sequence for devices which have a gate voltage (amps, doublers) will be:
The power down sequence should be those steps in reverse:
You can use HMC980, HMC981 and HMC920 active bias controllers, to implement the bias sequencing.
I'm using many chips and HMC_ALH382 is one of the chips, It needs +2.5V VDD.
But, HMC980, HMC920 chips support minimum +3V~4V.