Impedance matching nrf5340 with chip antenna and saw filter

[Dhruvit]

Hi everyone,

I'm designing a PCB using the nRF5340 MCU and the same matching circuitry (series inductor and parallel capacitor) with parallel ESD protection as provided in the nRF Thingy:91 reference design. I'm also using the same components: the 2450AT18D0100E chip antenna and the SAFFB2G45MA0F0AR1X SAW filter.

While reviewing the nRF Thingy:91 design files, I haven't been able to locate explicit mentions of 50-ohm impedance matching for the PCB traces.

My question is:

• Is additional impedance matching for the PCB traces truly unnecessary in this scenario, or might I have missed something during my examination of the reference design?

Thanks and regards,

[mathiaso]

Hi, Dhruvit.

You should indeed use a 50-ohm coplanar waveguide for your RF trace, as mentioned in this guide.

Best regards,
Mathias

[Dhruvit]

Hi mathiaso,

I have used same impedance profile as given in thingy91, as of i am using chip antenna 

for double check I have also matched in Altium for 50ohm and its nearby same trace width 

is it enough for maximum or nearby thungy91 rf output?

[mathiaso]

The trace dimensions giving a 50-ohm impedance will vary depending on PCB stack-up, material, etc. I recommend that you both use the tool in the Layer Stack Manager in Altium and that you check with your PCB manufacturer which dimensions will result in a 50-ohm transmission line on your PCB.