I have the QPA2609 LNA, have gone through its datasheet which mentions the requirement of bias sequencing. There’s also an application note from Qorvo for the same.
I would like to know, if using this in FMCW chain, is there mandatory need to have the bias sequencing circuit.
The above mentioned note already have the example circuit for the bias sequencing but as the LNA being a sensitive component was thinking of supplying ultra low noise LDOs for both the Vgs and the Vd supplies, but one among them is the buck converter ! Also got to know there are two ways for the bias sequencing,
Active bias sequencing - where focus is given on keeping the drain current constant
By keeping the Vgs constant
What shall be used ?
The same LNA is used in the paper but it didn’t quoted anywhere about the power sequencing.
The QPA2609 is a depletion mode device, so needs bias sequencing. If running continuous then this would only need to be at power up/down. Incorrect bias sequencing will likely cause high current damage to the LNA.
The app note you referenced (AN107) has the correct bias sequencing, but is not suitable for the QPA2609 as it just uses a fixed gate voltage.
The QPA2609 Idq/Vgq response will vary across devices, as well as over conditions like temperature. This means that your bias circuit needs some form of active bias. This is normally in the form of a current sense resistor in the drain feed, and some closed loop to adjust the gate voltage to maintain constant Idq.
For further information please contact appsupport@qorvo.com stating your company name and location.