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CC1101: Relationship between MAGN_TARGET and CARRIER_SENSE_ABS_THR

Brandon Van Pelt
Prodigy 30 points
Part Number: CC1101


If the CARRIER_SENSE_ABS_THR is disabled (0x08) would the MAGN_TARGET settings have any effect for the RF performance, or would it also be essentially disabled?

  • 0
    TI__Guru* 86741 points

    From the data sheet:

    "The MAGN_TARGET setting is a compromise between blocker tolerance/selectivity and sensitivity. The value sets the desired signal level in the channel into the demodulator. Increasing this value reduces the headroom for blockers, and therefore close-in selectivity. It is strongly recommended to use SmartRF Studio [5] to generate the correct MAGN_TARGET."

    That means that you should use the value given SmartRF Studio for this setting, even if you are not using CS.

    Siri

  • 0 in reply to Siri
    Prodigy 30 points

    For our project we are using ASK. From design note DN022:

    "3.1 AGC Settings The register settings provided by SmartRF® Studio have been optimized for 2- FSK/GFSK/MSK modulation and when using one of the preferred settings and only changing the modulation format to OOK/ASK, the AGC settings might result in unstable or non-optimum reception (i.e. degraded sensitivity)."

    "The optimum AGC settings change with RX filter bandwidth and data rate, but for OOK/ASK the following has been found to give good results:

    AGCCTRL2 = 0x03 to 0x07

    AGCCTRL1 = 0x00

    AGCCTRL0 = 0x91 or 0x92"

    Before finding the design note our team had already discovered we could achieve significant improvements over the default values for our automotive application by adjusting the settings in the AGCCTRL registers. 

    Our current settings: 

    AGCCTRL2 = 0x03
    AGCCTRL1 = 0x58
    AGCCTRL0 = 0xB2

    So back to my question, If the CARRIER_SENSE_ABS_THR is disabled (0x08) would the MAGN_TARGET settings have any effect for the RF performance, or would it also be essentially disabled?

  • 0 in reply to Brandon Van Pelt
    TI__Guru* 86741 points

    From the DN022:

    "AGCCTRL2.MAGN_TARGET[2:0] is used to set an on-chip target value for the peak signal amplitude. MAGN_TARGET is used by the AGC loop to set the correct gain."

    This means that the MAGN_TARGET setting will affect the RF performance (it is not only used as a mean to set the CS threshold)

    Also, please specify if you are using CC1101 or CC1101-Q1. Your post says CC1101, but you are referring to an automotive application.

    Siri

  • 0 in reply to Siri
    Prodigy 30 points

    Thanks for the explanation! We are using the CC1101, I brought up the Q1 variant with our hardware engineer. Our application is an in-cab device and the difference between 85c and 125c temp rating is not an immediate concern, but we will look into switching for the next hardware version.