About the receiving circuit of EVAL. What should I connect to the antenna? CIR or Coupler. Is LNA unnecessary?

[Mizum.1]

In Figure 2 of st25RU3993 DateSheet, the CIR is used in front of the antenna, but the coupler is used for T4 of EVAL.

I think if I want to use carrier cancellation, ​the Coupler needs to be used.

Which one is recommended?

Is LNA unnecessary?​

Does adding LNA increase the sensitivity?

Please tell me NF or device noise.

[Bart Herse · Accepted solution]

Hi Mizum.1,

Indeed , carrier cancellation requires a directional coupler. A 10 dB directional coupler is recommended. A 5 dB coupler would be possible as well but beware of the significant higher transmission losses that come with it. Components we have made experience with are from Anaren, Johanson Tech and RN2 although other manufactures might have suitable models too.

An LNA can help to boost the sensitivity but I recommend to use a model with a bypass.

Cheers,

B