• State Resolved
  • Locked Locked
  • Replies 1 reply
  • Subscribers 30 subscribers
  • Views 1539 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

IWR1642: Cascading two or more IWR1642 radar units

Shahaf Gargir
Prodigy 315 points
Part Number: IWR1642

Hello,

my customer would like to explore the possibility of cascading two or more IWR1642 radar units, such that the RF signals (of 77GHz) shall be exactly synchronized for both (or all) cascaded units.

The purpose of this is to obtain more real & virtual antennas to be processed in the 3rd FFT algorithm, for better spatial analysis.
In addition, we would like to obtain both elevation & azimuth information in addition to distance & speed.

the questions:

  1. Is it possible to synchronize one IWR1642 unit on another unit's RF signal?
  2. If so, how is it done. Can we use a common 40MHz or 50MHz oscillator in order to obtain that?
  3. If so, what is going to be the phase difference & jitter measured between two cascaded units (on the 77GHz signal),
    and is that jitter going to be sufficiently low to assure proper operation of "unit B" receiving reflected signals originated
    from the transmitter of "unit A" ?
  4. My first assumption is that the jitter is going to be too high to obtain reasonable results, therefore my next question will be:
    Is there a direct way to provide "unit B" with the 77GHz generated at "unit-A", such that both units
    use the same 77GHz signal generated in "unit A" to feed their Gilbert cell multipliers, (thus inhibiting the operation of the RF PLL(s) of "unit B")?
  5. If so, is it possible to make fine tunings such that coupled units are all aligned to the same phase

regards,

Shahaf

  • 0
    TI__Mastermind 37500 points

    Hello,

    In the current mmwave sensor products, RF signal synchronization is used with Cascade operation.   This is possible with the AWR1243P device only.  

    1) no the IWR1642 does not have an RF synchronization, however you can reduce the differences with multiple 1642 devices, by having a buffered external 40Mhz TCXO clock, that is AC coupled and driven to both devices CLKP, while the CLKM is Grounded.   Depending on your application, you can connect one IWR1642 SYNCOUT (Start of Frame) to the SYNC In of the mmwave Sensors, the Frame Start would be triggered by the external Sync Input.   The SYNCOUT on the master IWR1642 comes from a GPIO MSS application 0->1 ->0 transition.

    2) on the AWR1243P, the cascade operation is discussed in "spyy003.pdf"  "swra574"

       There are special signals to connect the ~20Ghz (divide by 4) RF chirp-frame configuration from a master to the slave mmwave devices.  Typically the FMCW_SYNCOUT or FMCW_CLKOUT pins are routed to power dividers, with matched trace lengths to each slave and master mmwave device.  This is used as a transmit reference, and also has a receiver reference.

    On each device there are FMCW_SYNCIN or FMCW_CLKIN pins that are the reference inputs of the chirp signal.

    On each device the CLKP is routed from a buffered TCXO, with delay matched traces to each mmwave sensor.

    On each device the master mmwave sensor SYNC OUT or some customer reference is used for Frame Start.   This is buffered and delay matched to each mmwave Sensor Sync Input.  

    3) If the board delays are controlled, the FMCW_SYNCIN or FMCW_CLKIN will have a delay related to the internal FMCW_SYNCOUT path, since all of the mmwave sensor devices will use the Input, the phase difference is controlled in the delay matched routing.   Related to the jitter of the 40Mhz clock, all of the devices receive the time aligned clock, there is an internal clock interface.   If the customer activates the OSC_ClockOut, and wants to have tuned delay lines for each mmwave sensor, this delay can be tuned.  In the current quad 1243P cascade board, this can also be tuned in a receiver software delay.

    related to the direct question of the receiver reference, please review the cascade materials in the swra574 document.

    4) the cascade approach described is the method to do this

    5) If the board design has matched lengths for the distributed FMCW_SYNCIN, SYNCIN_ and CLKP the larger phase offsets are compensated.  The antenna also has to have delay matching from the RF-Tx, RF-Rx of the mmwave sensor to the antenna ports.

    Regards

    Joe Quintal