Hello everyone,
This is my first post to AAC. Over the past few years I've reference these discussion boards rather frequently and I've found them to be quite informative.
I have been working on a wireless sensing application and have some general design questions concerning board layout and can't seem to find consistent guidelines from the various chip manufacturers. I'm looking for some guidance and recommendations to improve the outcome of my design.
Transmission Line Design Questions:
Board Layout Questions:
Any help is greatly appreciated!
P.S. I'm just a dumb mechanical guy...
This is my first post to AAC. Over the past few years I've reference these discussion boards rather frequently and I've found them to be quite informative.
I have been working on a wireless sensing application and have some general design questions concerning board layout and can't seem to find consistent guidelines from the various chip manufacturers. I'm looking for some guidance and recommendations to improve the outcome of my design.
Transmission Line Design Questions:
- I am calculating 50 Ohm Impedance using AppCAD with 4 layer board stack-up from Osh Park
- Should transmission line impedance be considered as a micro-strip or a wave-guide?
- When is one preferred over the other? And for my application, with a very short TX line, should I calculate impedance using a microstrip?
- Atmel Application Note AT02865 – RF design guidelines recommend treating the transmission line as a microstrip when W/H >= 2 and a gap of 4X the dielectric thickness. The Johannson reference design is a two layer board and uses a coplanar waveguide
- For best performance should I manufacture some PCB's with varying track widths / spacing and then use a VNA to determine the best dimensions? If so, is the length of trace important?
Board Layout Questions:
- Should I include a keep-out region under the antenna launch area under the (u.FL) connector or should I leave solid copper pour? If a keep-out is recommended, should it be applied to all layers?
- Should I extend the ground plane beyond the U.fl connector, or is the current layout okay in that regard?
- Should I stitch the grounds of top and bottom layers to the RF Gnd area, or just the Surrounding Ground on the Top Layer and leave the bottom disconnected in this area?
- Per guidance on Nordic Dev Zone, a left a solid copper pour under the BALUN on all layers. I also left copper pour on all layers under the transmission line.
- Layer 1 = Red (Signals / Gnd)
- Layer 2 = Green (Solid Gnd)
- Layer 3 = Orange (Power Planes)
- Layer 4 = Blue (two signals but mostly Gnd)
Any help is greatly appreciated!
P.S. I'm just a dumb mechanical guy...