RF/DC Ground Consideration

[lkjhgf]

In the application where there are RF components with DC bias, do we need to keep seperate RF ground and DC bias ground??

If yes then what is the specific reason for that?
Where the RF gnd should be and where should be DC bias gnd?
Ground pouring on the top layer should be RF gnd or DC gnd?

I have one RF LNA IC working at 8 GHz frequency, which has no reference pin mentioned for ground. It has ground paddle where it is specified RF/DC gnd and also has supply pin to which there is a decoupling capacitor connected whose other end will be DC bias ground. So which ground will the IC consider as a reference for signal?

What are the effects when the RF/DC ground are the same?

Please help me with your valuable suggestions.

 

[ikevin]

RF_GND and DC_GND must be connected at some point, otherwise they will have different references and that might burn your circuit. Usually you route your RF signals with reference to RF_GND plane then everything else you reference to some other ground plane, let's call it DC_GND. Finally, connect those 2 ground planes through a big resistor maybe 1/4W 0805, depends on your application. This a method to minimize the amount of noise going from one plane to another plane.

Another way of doing this is to have a RF transformer where you isolate the RF_GND and DC_GND completely. When you choose the RF transformer, make sure to pick the correctly frequency for your application.