a question for pcb
As shown in the attached picture, the PA is in QFN package, with 3 stage amplifier inside. Each stage has its own gate and drain pins.
In order to reduce the footprint area, I would like to connect all gate pins together, as well as connect all drain pins together, so can I just add one set of the by-pass capacitors, like in (b), to the gate and to the drain pin? Since the DC power to each gate or drain is the same, one set of the by-pass capacitor would be enough for filtering?
Also, can I just make the PCB layout like (c)?
Well i would not suggest option "c" at all. all the stage sould be decoupled separately.
Thanks Dipnirvana.
Another questions about the decoupling capacitor. Can I just connect the 0402 100pF capacitors adjacent to each Vdd and Vgg, and then tied them together, and connect the tantalum 2.2uF capacitors at the common joint?
In this case, the 100pF provide some decoupling between different power pin, and the 2.2uF provide further futhering from the DC power line.
Well my friend capacitor requierment comes from the current switching requierment of the particular IC. may be single 2.2uF enough for the application. But i would say if "a" is proposed by the vendor, just go for it.
How did you connect the decoupling capacitors to the ground ?
This is extremely important depending on the frequency of interest. if you use signle via, this will bring you some inductance effects so this PA may oscillate. Connections must be done very carefully and straightforward.Because RF currents ( especially harmonic currents ) should be tied to the ground very shortly..