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Low dynamic measurement of RSSI on CC1120

Axel Lavroche
Prodigy 130 points
Other Parts Discussed in Thread: CC1190, CC1120
hello,

We use a CC1120 that perfectly receive 434Mhz but we have a problem with the values ​​of RSSI .

The indications are correct once the offset adjusted but the dynamic is not there . We will as about -80 to -120dBm . Impossible to go over the -80dBm. So dynamic of 40dB instead of 70dB in the worst case.    .
(values read on RSSI0 and 1 are Ox214 for an AGC_GAIN_ADJUST register of 0 in the case of saturation to -80dBm : So Ox214=532*0.0625=33.25-102(offset)-15(custom adjust for extern LNA) = -83dBm value of saturation for us. )

We use a configuration 4GFSK 163.2kbps Chan_BW = 200kHz .

The value of " AGC_REFERENCE " has been adjusted for an external LNA (16dB) . The AGC registers are configured in this way :
CFG0 = CB
CFG1 = A9
CFG2 = 20
CFG3 = 91

Thanks to explain us what register can be influence the dynamic of measurment of RSSI.

Best regards,

ps : We have try to change the IF_Config that is the value by default or the configuration of DC_Filter but any results on RSSI dynamic
  • 0
    Prodigy 130 points
    I always to say that we have try with values issued of Smart RF for AGC but it don't work too
  • 0 in reply to Axel Lavroche
    TI__Mastermind 39860 points
    Did a measurement in our lab using CC1120+CC1190 and got the expected RSSI reading vs input power level. When using zero-IF the RSSI saturated at approx -50 dBm as expected.

    Please provide a plot of RSSI reading (converted to dBm) vs input power level. Include also the register settings used.

    Have you tried to use TrxEB + SmartRF Studio to control the chip and do the RSSI reading? That is, strap wires from TrxEB (SPI + GDO lines) and use a good known SW (i.e. SmartRF Studio) to control the board. The way I read you e-mail you have developed HW and SW and you are trying to debug both at the same time. When doing HW debugging use a good known SW (Studio). Conversely, when debugging SW use a good known HW (e.g. TrxEB + CC1120EM). Right now we do not know if your problem is HW or SW related.
  • 0 in reply to Sverre
    Prodigy 130 points
    the plot is really simple : saturation at 83.5dBm and correct RSSI returned up to -105dBm after that no reception so no RSSI returned. Sometimes a -110dBm or near is returned.

    We can't developped hardware with smart rf studio software. We have a sensivity and a behaviour of our product really good and as datasheet but not for the RSSI and his dynamic.
    We always search which parameter can influence this data.

    If it was Hardware problem we shouldn't have the very good behaviour on all other caracteristics i think.
  • 0 in reply to Axel Lavroche
    TI__Guru**** 317180 points
    AGC_REF should not be adjusted by the gain of the LNA. Use the equation in the UserGuide.

    It looks like your AGC settings is for a much lower datarate, have you tried the AGC_CFGx settings SmartRF Studio suggest for the 200 kbps setting which is close to what you need?