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CC2642R-Q1: Out-of-band blocking of CC2642 and RSSI

Albin Zhang
Expert 5860 points
Part Number: CC2642R-Q1
Other Parts Discussed in Thread: CC2640

Tool/software:

Hi, 

1. could you elaborate the parameter of the Out-of-band blocking? 

e.g. if inject a strong jammer signal between 1.3~2GHz, below 10dBm， does it mean there is no any impact? or the wanted signal sensitivity drop to -67dBm? 

2. Why a Jammer will impact the RSSI reading? (about +40dB)

BR. Albin

  • 0
    TI__Intellectual 1280 points

    Albin,

    1. The out of band blocking specifications detail the power level the device can withstand without interfering with communication. So from the table you've provided, for 30MHz to 2000MHz, if an interferer is present and stays below -10dBm there should be no degradation in communication.

    2. If a large out of band jammer signal is present, it can increase the noise floor of the CC receiver and interfere with communication. Especially if the received signal is near the noise floor. 

    Andrew 

  • 0 in reply to Andrew Lugo
    Prodigy 40 points

    Hi Andrew,

    1.Is RSSI measured as intensity of sum of both wanted signal and noise from blocking signal. Why is my test, RSSI decreased about 8dBm when blocking signal between 1.3GHz~2GHz was added?

    2. Is there any document that shows how RSSI is get in detail.

  • 0 in reply to Fantw
    TI__Intellectual 1280 points

    Albin,

    1. Can you please provide more details of your test. 

    a. Are you using Smart RF studio?

    b. Is your wanted signal modulated or unmodulated?

    c. Is the tone CW or are you sending data packets?

    d. What is the power level of the blocking signal?

    e. What is the bandwidth of the blocking signal?

    f. What is the RSSI value of the wanted signal without the blocking signal present?

    g. Are you using the 1M or 2M phy

    2. There is no document that I'm aware of that provides details of how RSSI is computed. 

    Andrew

  • 0 in reply to Andrew Lugo
    TI__Expert 5860 points

    Hi Andrew, 

    Thank a lot for follow up. 

    The ?? ? should be the customer reported the phenomenon. I will ping him to reply directly. 

    BR. Albin

  • 0 in reply to Andrew Lugo
    Prodigy 40 points

    Hi Andrew, Albin,

    a. Smart RF studio was not used. CC2640 was set in Rx by customer's software.

    b. Wanted signal was modulated and transmitted by CMW500.Its antenna was put about 8cm to DUT. It could be received by app in mobile phone such as LightBlue.

    c.

    d.The blocking signal was sent by a horn antenna about 1m to DUT. I see in GM's EMC STANDARDS that it's 70 V/m.

    e. I see in GM's EMC STANDARDS that the blocking sinal is " CW, Pulse Modulation (PM) Pulse Repetition Rate (PRR) =217Hz, Pulse Duration (PD)= 0.57ms "

    f. CMW500 was put near DUT, and the RSSI was about -17dBm typically without blocking signal.

    g. Using 1M phy.

  • 0 in reply to Fantw
    TI__Intellectual 1280 points

    Fantw,

    Thanks for the information I will need to discuss this issue with some experts on my team and get back to you.

    Andrew

  • 0 in reply to Andrew Lugo
    TI__Intellectual 1280 points

    Fantw,

    Does this mean your blocking signal is about +40dBm before taking into account the gain of the horn antenna? Also what is the gain of your horn antenna? Is communication being lost when the interferer is present or is the only issue that the RSSI value is lower? It sounds like you're oversaturating the RF front end and it's affecting the accuracy of the RSSI calculations. Transmitting a 40dBm signal 1m away from the device will result in an out of band interferer well above the -10dBm limit called out in the datasheet for the band of your interferer.  Going above this limit can and will degrade communication performance and can result in the strange behavior you're observing. 

    Andrew

  • 0 in reply to Andrew Lugo
    Prodigy 40 points

    Hi Andrew,

    Thanks for your reply. No error in communication or maybe no communication since DUT only receieves wanted signal and sends RSSI to upper tester. If it's because input power is larger than -10 dBm, is there any measures except add a filter in RF frontend.

  • 0 in reply to Fantw
    TI__Intellectual 1280 points

    Fantw,

    Yes, reducing the signal level of the interferer signal being received by the CC device is the only measure that you can take to reduce these affects. Adding additional filtering and adding a metal shield around the CC device would be the 2 primary ways to accomplish this. 

    Regards,

    Andrew

  • 0 in reply to Andrew Lugo
    Prodigy 40 points

    Hi Andrew,

    How can we explain RSSI will reduce if interferer signal is larger than -10dBm. Would you check whether my idea meets the fact. In my opinion, when interferer signal becomes larger, LNA will work in nonlinear area, 2rd and 3rd harmonic in output increase, this make AGC lower LNA's gain, so the power of wanted signal reduces. Is there a low-pass filter after LNA that will filter harmonic. 

  • 0 in reply to Fantw
    TI__Intellectual 1280 points

    Fantw,

    I think your assumption about the effects of the intefererer on the LNA, driving it into the nonlinear region and affecting it's gain are probably correct. I can check with the design group on this topic but their response may be delayed.  

    Regards,

    Andrew