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CC1125 Cat 1 Development kit sensitivity and ACR

JBD26
Prodigy 170 points
Other Parts Discussed in Thread: CC1125

Hello,

I have not been able to achieve the sensitivity and adjacent channel rejection performance reported in application note AN122. To measure the sensitivity I am using the CC1125 Cat 1 development boards for a transmitter and receiver. The dev boards are placed in metal boxes to minimise radiated signals. An RF cable runs between the two boxes and I insert RF attenuators in the conducted path to reduce the signal until the sensitivty limit is reached. Using ETSI CAT1 869MHz 4.8kbps settings from RF studio (Ver 1.14.1) I can only achieve -109dBm sensitivity rather than the -115dBm expected.

I am also not achieving the adjacent channel rejection reported in AN122. My results are about 10dB worse than expected.

Is there anything obvious that I may be missing?

 

 

  • 0
    TI__Mastermind 18780 points

    Are you baisng your sensitivity on the RSSI value or the number and size of attenuators? If iyou use the latter, the noise figure of the attenuators must be taken to consideration as well. What kind of attenuators are you using? Typically, when adding a lot of attenuaters in a row will make the attenuation so big for the signal that you will get some of the signal going through the air instead of the cable. This will typically reduce the performance.

     

  • 0 in reply to CHS
    TI__Mastermind 39860 points

    Are you using SmartRF Studio for your testing?

    Please note that the app note provides the sensitivity as 1% BER. For ACR the interferer is increased until BER = 1%. SmartRF Studio uses packet error rate (PER) in Packet TX / Packet RX.

    PER = 1 - (1-BER)^n, where n is the payload data. As an example, 3 byte payload and 1%BER corresponds to 21%PER

  • 0 in reply to Sverre
    Prodigy 170 points

    I am using fixed SMA attenuators by Mini Circuits (eg VAT-30+) I add up to 6 of these in series to increase the  attenuation to reach the sensitivity level. I have also tried generating the wanted signal using an RF signal generator to FSK modulate a baseband 4.8kbps packet. By adjusting the signal generator power output level I get very similar results to the attenuator method. I am still about 5dB worse for sensitivity and 10dB worse for ACR than expected.

    The RSSI level shown in RF Studio is about 8-9dB less than the signal I have measured going in to the SMA connector on the DEV board. I think this is expected since I have not calibrated the RSSI in any way and the losses through the SAW filter need to be accounted for.

    I have been using the default 30 byte payload packets for these measurements and using a 20% PER criteria. If I reduce the payload to 3 bytes (still using 20% PER) I measure a 1-2dB improvement in sensitivity.

    I am still not close to achieving the ACR limits required for Category 1 (about 10dB out). Can anyone provide any advise on how to achieve better results from the Cat 1 Dev kit? 

     

  • 0 in reply to JBD26
    Prodigy 170 points

    An update:

    I have repeated the ACR measurements on the Cat 1 dev boards using a different signal generator to produce the interfering signal and I now get results much closer to expected. It appears that the signal generator I was using originally does not produce a spectrally pure enough signal for this test.

    Thanks for the replies - they were also very helpful.