output power exceed +4dbm after matching circuit

[welsonliu]

when design the product, BLE output power set at +4dBm, and test the real output power with Spectrum Analyzer. when test at the MCU direct output pin the output power is about +3.5dBm, but when test after matching circuit, the output power is about +4.7dBm, the output power exceed the MCU output power, why this happens? Normally, the output power should  attenuation when after the matching circuit, i did not use a PA amplifier...

[run_ar]

Hi,

We always measure output power after the matching circuit as that provides the best working conditions for the radio front end. Measuring without the matching circuit will normally give you lower output power due to improper matching.

Also there are chip to chip variations. So there will be better performing chips that has an output power that is greater than 4, and there are lower performing chips that has an output power that can be lower.

[welsonliu]

Thanks, yes, you are right , i can not test the output power without the matching circuit...

when i saw the datasheet of 52840, i found it say the RF power accurancy is +-4dB, i can not understand what this means, 

does it means the output power has so much error??

see the picture i redline this parameter...

[run_ar]

We are testing and screening for output power in production. At room temperature we have a normal distribution where most products are within +/- 2 dBm (Likely closer to +/- 1.5 dBm). You can have some out layers, mostly at the lower end. In addition the output power depends on temperature. i.e. it is higher at low temperature and lower at higher temperature. Seems the difference is about 0.5 dBm in average for 4 devices between -40 degrees C and +85 degrees C.  In addition to this the product specification has some additional margin for error.

[welsonliu]

Thanks very much for your kind help.