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IWR6843AOP: Max output power for regulatory compliance

Jeff Marsar
Prodigy 30 points
Part Number: IWR6843AOP

Hello,

My team and I are trying to verify that our application meets an FCC radar output power requirement and have a few questions. Specifically 3.2.2 in this TI document:
https://www.ti.com/lit/an/spracp3c/spracp3c.pdf?ts=1665498950691&ref_url=https%253A%252F%252Fwww.google.com%252F

Device datasheet: https://www.ti.com/lit/ds/symlink/iwr6843aop.pdf?ts=1667490529439

1. Is the single transmitter output power EIRP of 15 dBm out of the chip package or out of the antenna?

2. If multiple transmitters are energized at the same time, how does that factor into our calculations?

3. The formula for power density in the reference document defines R as the minimum separation distance. Is that the separation from the energy source to the target? Section 3.1.2

4. Does distance to the target factor into the average and peak TX power requirements listed in section 3.2.2?

5. A software teammate received advice from TI about setting the output power to 10. The suggestion was to set register 'txOutPowerBackoffCode' to 0x0A0A0A, with the intention of setting each antenna to 10 dB (0x0A). I am confused by that since the documentation refers to this setting as a backoff, "how much the transmit power should be reduced from the maximum". Thus, a setting of 0x0A would not set the power to 10, but set the power to (max - 10). Can you clarify?

Thank you!

Jeff

Norbert Health

  • 0
    TI__Mastermind 37805 points

    Hi,

    An expert will comment shortly.

    Best,

    Nate

  • 0 in reply to Nathan Block
    TI__Mastermind 37805 points

    Hi Jeff,

    Jeff Marsar said:

    1. Is the single transmitter output power EIRP of 15 dBm out of the chip package or out of the antenna?

    EIRP is radiated power out of the antenna

    Jeff Marsar said:

    2. If multiple transmitters are energized at the same time, how does that factor into our calculations?

    As this app note states: "Additionally, if using multiple transmit antennas at once for BPM-MIMO or beamsteering, there is a factor of 10log10(Nantennas) that is added to account for constructive interference. Gantenna, multiple simultaneous transmitters= Gantenna, single transmitter + 10log10(Nantennas)"

    Jeff Marsar said:

    3. The formula for power density in the reference document defines R as the minimum separation distance. Is that the separation from the energy source to the target? Section 3.1.2

    I believe so.

    Jeff Marsar said:

    4. Does distance to the target factor into the average and peak TX power requirements listed in section 3.2.2?

    No, these are measured on the output of the device. Radiated measurements will likely be adjusted to account for the attenuation of free space when calculated.

    Jeff Marsar said:

    5. A software teammate received advice from TI about setting the output power to 10. The suggestion was to set register 'txOutPowerBackoffCode' to 0x0A0A0A, with the intention of setting each antenna to 10 dB (0x0A). I am confused by that since the documentation refers to this setting as a backoff, "how much the transmit power should be reduced from the maximum". Thus, a setting of 0x0A would not set the power to 10, but set the power to (max - 10). Can you clarify?

    Your understanding is correct. A value of 0x0A0A0A would be the maximum of around 12-13 dBm (varies by device), minus 10 dB for a value of 2-3 dBm, For 10 dBm of transmit power, you would use a value of 0x030303 to get 9-10 dBm of output power.

    Best,

    Nate