The Designer's Guide Community Forum

The Designer's Guide Community Forum
https://designers-guide.org/forum/YaBB.pl
Design >> RF Design >> RF design tips
https://designers-guide.org/forum/YaBB.pl?num=1192091944

Message started by imett on Oct 11^th, 2007, 1:39am

Title: RF design tips
Post by imett on Oct 11^th, 2007, 1:39am

hello to everyone,
i'm a new rf designer and i've to ask some question about the rf design layout that i don't understand:

in many rf boards (evaluation boards) there is a hole , not plated, near the rf components like ad8353...LMH6624 etc

usually for RF i use a pcb with all the bottom connect to ground and a spot top ground; to avoid the ground loop i've to connect the active components to the top ground or with a vias to the bottom?

many board use ,for a signal trace, use many vias to ground to reduce the ground impedence, it is necessary use thi technique?

Thanks in advance.
Matteo

Title: Re: RF design tips
Post by didac on Oct 15^th, 2007, 1:58am

Hi imett,
I was waiting to see if someone more experiencied than me could help but I will try anyway. When you are talking about in which ground you should connect the component I really don't understand what you mean, there's only one ground, the ground plane in the bottom; the component should connect to a copper spot filled with bias to make a good (ideally free of parasitic) ground.
My suspect about this hole you see at evaluation boards is that it's a non-standard fiducial mark for automatic pick&place machines(usually local fiducial for fine pitch component is a solid circle of copper with solder mask cleared and a good clearance, but I see machines that are able to handle with any geometry).
You said that many board filled the ground along the signal trace with bias,are the using this configuration?:
GND
SIGNAL
GND
if so it's a coplanar line, and yes you should fill with vias(every lamba/20 or so). If you use microstrip ground must be placed at a safer distance from the signal trace because calculations of impedance assume that only the ground plane in the bottom layer is present.

Other questions arise if you have in the same board RF,power and digital circuits. Then power and ground usually are splitted and connected in
a star point.
Hope it helps,
PD:there's a tutorial about RF design available atwww.jlab.org/accel/eecad/pdf/050rfdesign.pdf

Title: Re: RF design tips
Post by xutangyi on Jan 12^th, 2008, 6:46am

dear sir
I'm a new designer of the rf ciruit,i learned a lot of rf module designer in the designer's guide,but i want to know the have some other forum to discuss the rf module design.such as:the module about the HPA(Output power is about 5W,the design about lna module) pls tell me some place to learn. thank you very much(I'm a chinese engineer)