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CC2400 RSSI odd behavior

Eric S
Expert 5550 points
Other Parts Discussed in Thread: CC2400, CC2500

I'd like to help my customer get clarity on a couple of specs on the CC2400.   Please help clarify as soon as possible.

 

 

 

1)      Image Channel Rejection @1Mbps is speced at 21dB

I assume this is the mixers image output is that true? if not please clarify this spec.

 

2)      Image Frequency Suppression is speced at 56dB

I am unclear on this spec. Is this further rejection of the image frequency done in software filtering? Please help clarify this.

 

  • 0
    TI__Expert 3205 points

    Hi Eric

    Image Channel rejection is the level of a modulated interferer signal at the image channel while a wanted signal 10dB above the sensitivity limit is received in the wanted channel.

    I.e at 1Mbps an interferer signal < (-87+10+21= -56dBm) should hold no significant influence on communication in the wanted channel at -77dBm above -56dBm the interferer signal will block communication.

     

    Image frequency suppression is the ratio of a signal being received at the image frequency the receiver sensitivity in configured frequency with no signal at this frequency.

    I.e. a (-87+56=-31dBm), 1Mbps a signal at the image frequency will be perceived by CC2400 as a -87dBm signal at the wanted frequency. Note, bits will be inverted when receiving a signal on image frequency.

     

    A >-20dBm signal at any frequency within ±50MHz will block communication when wanted signal is 3dB above sensitivity limit. A RSSI increase is also expected when this strong signal is imposed to CC2400 within this frequency range. That the image frequency (-2MHz) gives the highest RSSI reading is also expected

     

    Note, CC2400 is currently not recommend for new designs. A newer alternative might be the CC2500.

     

    Regards

    Tor-Inge