NRF51822-CFAC-WLCSP + BAL-NRF02D3 + onboard PCB (passive antenna)+ 2layer flex PCB

[Bhaskar]

Hi,

I'm designing a 2 layer flex PCB with the nRF51822-CFAC WLCSP package and recommended ST BAL-NRF02D3 balun and on-board PCB passive antenna (not ceramic chip antenna) with pi network for tuning.I have a couple of questions.

1. How to achieve 50 Ohm transmission line impedance to match on both nRF side, and the antenna side to meet 20m distance. its a completely flex PCB of 2 layer (not a rigid PCB) and all components should be mounted on flex PCB only.

2. What reference files should i consider to satisfy my requirement. Let me know is there any design reference available.. My project running with critical deadlines..Please help me how to proceed..

Thank you....

[Einar Thorsrud]

I do not think there are any particular things you need to think of when using a Flex PCB compared to a normal rigid PCB. The only thing is that you need to tune the impedance trace to match the material and thickness of the PCB, as Dave_couling wrote.

You can download the nRF51x22 CxAx Reference Layouts here.

[Einar Thorsrud]

A properly tuned λ/4 printed monopole antenna, such as the one that is used in the nRF51 DK has a good efficiency. I am not an antenna expert, but I would be surprised if you could gain much using a different PCB antenna shape. The most important is to let have a decent distance to ground and that the antenna is as straight as possible. (The performance is better if the antenna has a 90-degree angle to the ground plane, but a normal PCB antenna is naturally parallel to ground.)