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Original question:

IWR1843: Transimit the FMCW signal at very high speed

IWR1843: FMCW ramp generation

John Schindler
Prodigy 20 points
Part Number: IWR1843

Tool/software:

I think this is related because I'm trying to better understand the ramp generation alluded to in the original question.

I found a working sensing estimator at https://dev.ti.com/gallery/view/mmwave/mmWaveSensingEstimator/ver/2.4.0/.

On the defaults for the xWRL6432 device it shows 

maximum range = 6.543 m => round trip time = 43.6 ns

Sampling Rate (Ms/s) =3.030 => sampling time = 330 ns

Is the Sampling Rate the rate at which the DAC or PLL output changes? If so, is it smoothed so that the frequency is not constant for the transit time?

Thanks

John

  • 0
    TI__Mastermind 23177 points

    Hello John,

    The sampling rate is the rate at which the ADC samples the incoming IF frequency, the DAC and PLL is for output. Can you elaborate on what you mean by smoothing? The mmWave Radar device is FMCW and we define a frequency start and constant frequency slope which can eventually give us a resulting carrier frequency and end frequency. 

    Best Regards,

    Pedrhom

  • 0 in reply to Pedrhom Nafisi
    Prodigy 20 points

    (Sorry if this appears twice; I initially replied with my mail client but it did not appear here.)

    Hi Pedrhom,

    I'm not sure about this device, but I have seen several where basically a DAC generates the ramp for the modulation. The DAC steps usually last longer than the transit times, at least for small target distances.(microsecons vs. nanoseconds)
    This would mean that the frequency does not change and there will be no IF generated. There will of course be some cases where the transit time spans the step change in frequencies but it seems risky to rely on this.
    Since FMCW obviously works, I must be missing something--I hope you can set me straight.
    Best regards,
    John
  • 0 in reply to John Schindler
    TI__Mastermind 23177 points

    Hello John,

    We have this Radar Academy page that covers the FMCW process our device does in decent detail but not overly low level. Feel free to look at the other modules in the Radar Academy for more information on varying levels of detail. Let me know if you need supplemental explanations.

    https://dev.ti.com/tirex/explore/node?a=GwxShWe__2.10.00.2&node=A__AXNV8Pc8F7j2TwsB7QnTDw__RADAR-ACADEMY__GwxShWe__2.10.00.2

    Best Regards,

    Pedrhom