antenna circuit capacitor tolerances

[FredNovalia]

Hi,

Our manufacturer would like to change the recommended capacitors on the nRF51822 antenna circuit design. Here is the query:

Please check below 3 capacitors request +/-0.1pF , which are not regular/popular spec., not only the price will be 2 or 3 times higher, but also the lead-time will be longer at least 6 weeks up. Can you use/accept +/- 0.25pF tolerance ? 2.2pF MULTICOMP MCHH15N2R2B500LT Capacitor, NP0, ±0.1pF 1.5pF MULTICOMP MCHH15N1R5B500LT Capacitor, NP0, ±0.1pF 1.0pF MULTICOMP MCHH15N1R0B500LT Capacitor, NP0, ±0.1pF

What would be the risks in changing those tolerances? Could you suggest some alternative capacitors, cheaper and readily available?

Thanks for your help,

Fred

[Locky]

These are fairly standard tolerances for precision RF tuning components. It is likely you PCB specs will have a much larger variation than these values i.e. the impedance of your RF trace. The main questions you have to ask yourself are:

1. What volume are you producing? More volume = More potential for full spectrum variation
2. What RF performance variations are you currently seeing across a production batch?
3. What is acceptable RF performance variation to you / your customers?

Likely you won't see much difference in a 0.25pF VS 0.1pF tolerance. But RF is black magic until you actually test ;)

[FredNovalia]

Thanks for the advice. We will go into full production (>10000) but hopefully we will get a test batch from the manufacturer.

[Asbjørn]

I would agree with @Locky here. If you want to change component manufacturer and tolerances, make sure that this would still be ok with regard to performance of your boards. Usually it won't be a problem, but as Locky states, testing is important here. If you are fine with potentially larger variations in a batch, but still with all of them within acceptable performance, there's nothing wrong in switching supplier. The risk is that output power, sensitivity, attenuation of harmonics could vary more across your boards along with the higher tolerances that you introduce with the new components.

I don't have any specific component recommendation, but I would recommend you to test with the new components before you go into production.