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TDC7200, Mutiple reflected signal measurement

Shinichi Inoue
Guru 21556 points
Other Parts Discussed in Thread: TDC7200, TDC7201

Dear Spacialists,

My customer is considering TDC7200 for LIDAR.

He has question about multiple reflected signal measurement.

Could you please advise?

(1) The datasheet of P1. says "supports up to 5 signals", 

He thinks this means multiple reflected signal.

On the other hand, datasheet P.5, 7.3 recommended Operating Conditions of Minimum Time between 2 stop signals, describes  minimum 67ns.

In case of LIDAR, 67ns means 3 x 10^8 x 67 x 10^(-9) = 20.1m.

TDC7200, when using multiple optical reflection, can't it measure less than 20.1m? 

(2) Do you have any solution for reducing minimum time between 2stop signals 67ns?

If it can't be impossible, it seems to be not suitable for LIDAR.

I appreciate your great help.

Best regards,

Shinichi 

  • 0
    TI__Mastermind 21685 points
    Hello Shinichi-san,

    Yes, minimum time between 2 stop signals is 67ns. If stop signals are closer than 67ns, one solution is to use two TDC7200s with common start. TDC1 would measure start to stop1 time and TDC2 would measure start to stop2 time.

    FYI, we also have a 2 channel TDC device called TDC7201. It has two builtin TDC channels that you can use to overcome the 67ns minimum time between 2 stops.

    www.ti.com/.../description

    Other workaround option is to introduce a known fixed delay so stop1 to stop2 is greater than 67ns.

    Please check this app note also

    www.ti.com/.../snaa292

    Thanks,
    Vishy
  • 0 in reply to Vishy Viswanathan
    Guru 21556 points

    Dear Vishy

    Thank you for your reply.

    A minimun time is 67ns for one TDC7200.

    By using two TDC7200s, it can be reduce.

    I also introduce TDC7201, I think it is more suitable for LIDAR.

    I am going to send your recommended two documents.

    If customer has addtional question, I'll ask again.

    I appreciate your great help.

    Best regards,

    Shinichi