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 ;)