LNA PCB layout

[Leiser]

Hi,

I design LNA´s for the automotive market. I have a dimension constraint. Does anyone know if it´s possible to design a LNA (174-864MHz) on one side of the PCB and a FM LNA on the other one?? I thought than using 4 layer PCB with two internal ground planes could be an option, however I have never done it before and I don´t know if what I´m saying is just not possible. My worries are if amplifiers will affect each other.

Thanks in advance.

 

[Comcokid]

I would say it's possible, depending upon how much gain each LNA has. Like any LNA, high-gain may dictate shields or other isolating techniques to prevent oscillation from parasitic feedback.

I've designed several 2.4 GHz LNAs on double sided material keeping one side ground plane. Layout's a little tricker but you can do it. Nothing inherently wrong with having two ground planes. Any ground stitching vias may have to be thought-out carefully since blind vias would be cost prohibitive for automotive.

A wild thought - you could make the two LNAs on double sided thin material, and as a final PCB assembly step break and fold the two PCB back-to-back with a drop of glue, RTV, or doublesided tape to create your "4-layer" board assembly.