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IWR6843ISK: RX and LO behaviour when all TX channels are turned off

Dante Spack
Prodigy 10 points
Part Number: IWR6843ISK

My current configuration is simple: I have a DCA1000 and an IWR6843ISK. I am doing research on the use of TI's FMCW radars as measurement devices. I am aware that this is NOT a typical way to use mentioned hardware.

For the reason mentioned above, I have turned off all TX channels in mmWave Studio, and I have turned on one RX channel, namely the first one (RX0). This works and I am able to do everything within the mmWave Studio software as expected.

I am curious about the RX/hardware behaviour in my scenario:

  • Firstly, if all TX channels are turned off, what is my RX mixed with? I am assuming an LO, but TI's FMCW fundamentals mention that RX and TX are mixed for each chirp.
  • Secondly, how does the LO behave for one RX channel, assuming that the RX and LO are mixed for each chirp?
    • Does the RX/LO "sweep", just like how a TX channel would transmit a synthesized signal? E.g. the LO increases linearly with small increments, like a modulated chirp would.
    • Or does the RX's LO "jump" for each chirp? E.g. the LO increments for each chirp?

I think that the latter (LO increments for each chirp) is true, but I am unsure. I have created an image to better express what I think is happening:

I have been going through the TI's FMCW fundamentals and the IWR6843ISK datasheet, but I was unable to find any information regarding my question.

  • 0
    TI__Mastermind 31680 points

    Hello User,

    Thankyou for reaching out onTI E2E Forums!

    I understand you're new to FMCW radars and TI mmWave Sensors and as a first step, we would like to introduce you to our mmWave Training series that is specially architected by our team for beginners like you. 

    Here is the link to the series : https://training.ti.com/mmwave-training-series 

    We believe you'll get a better understanding on FMCW Radars with this.

    Please let us know your insights and and feel free to reach out to us again in case you still need any clarifications or if you feel your questions are unanswered. 

    Thanks and have a good day!

    Regards,

    Ishita 

  • 0 in reply to Ishita Kochar
    Prodigy 10 points

    Thanks for your reply: I've already followed the training series but my question still remains the same.

  • 0 in reply to Dante Spack
    TI__Mastermind 25835 points

    Hello Dante,

        As you could see in the block diagram, Even if the Txs are off LO would be fed to mixer, Here LO would be a ramp generator, same would be fed to mixer to generate the IF signal.  LO would increases linearly with small increments, like a modulated chirp would do.

    However in the RF Rx signal path there are no Tx signals coming back as a reflection you would get just noise.

    Could you please elaborate what is your ultimate motive of this question?

    Thanks and regards,

    CHETHAN KUMAR Y.B.