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TDC7201: Multiple Pulses measurements

Elad Bar
Prodigy 205 points
Part Number: TDC7201


Hi,

 

I have a question from one of my customers.

We want to measure the time of flight for more than single pulse, for example 5 or 10 pulses, one after the other and average the results so then we could read the average result for few pulses.

Can you help us with the configuration?

Where can I find information about it?

 

Thanks,

Elad

  • 0
    TI__Mastermind 31655 points
    Hello Elad,

    I'm going to assume that you mean they would like to average several cycles of measurements, each with a START and STOP pulse and its own TOF. This functionality is built in to the TDC7201 and is called multi-cycle averaging. In this mode, the TDC7201 will record however many cycles are set (from 1-128 cycles), and will average the TOFs of all the cycles, only sending an interrupt for measurement completion when all cycles have finished. You can find more information in the datasheet section 7.4.4 Multi-cycle Averaging (www.ti.com/.../tdc7201.pdf)

    If you mean to measure multiple STOP pulses after a single START pulse, this can be done by setting the NUM_STOP register which can record up to 5 STOP pulses per START pulse.
  • 0 in reply to Scott Cummins
    Prodigy 40 points
    Hi,
    Is multi-cycle averaging mode can work together with combined measurement mode?

    From TDC7201 datasheet:
    7.4.4 Multi-Cycle Averaging
    In the Multi-Cycle Averaging Mode, the TDC7201 will perform a series of measurements on its own and will only
    send an interrupt to the MCU (for example, MSP430, C2000, and so forth) for wake up after the series has been
    completed.


    8.2.2.1 Measuring Time Periods Less Than 12 ns Using TDC7201
    The minimum time measurable in measurement mode 1 is 12 ns. It is feasible to do measurements down to 0.25
    ns using the TDC7201 in what is called combined measurement mode. In combined measurement mode,
    START1 and START2 are connected together:
  • 0 in reply to ARTHUR BERKOWITZ
    TI__Mastermind 31655 points

    Hi Arthur,

    Since the TDC7201 essentially works as two independent timing channels using the multi-cycle averaging in combined mode will depend on how the devices are connected to the LIDAR AFE and the microcontroller being used. Each channel will begin a new measurement cycle and send out a new trigger as soon as possible after completing the first measurement. Since STOP1 (essentially the combined mode START for purposes of measuring TOF) will occur first, the trigger signal of TDC1 will be output before the trigger signal of TDC2. Once the trigger is sent out, the TDC will simply wait for the next START signal which should be the reference START supplied by your microcontroller. So in this case, the microcontroller should only send the reference START after receiving both trigger signals to make sure that both TDCs are ready for the next measurement to begin.

    This requires that the microcontroller still be active for each new measurement cycle, so if the reason for using the multicycle averaging is to reduce power consumption by allowing the microcontroller to sleep for several measurement cycles, this will not have the desired effect.

    So the short answer is, yes, you can use both multi-cycle averaging and combined mode together, but just make sure that the reference start is only sent out after both TDCs are ready to begin the new measurement.

    Regards,

  • 0 in reply to Scott Cummins
    TI__Intellectual 1600 points

    Hi,

      I have a further question. My customer is for LIDAR application, they want to know what's the shortest pulse repeat frequency( the fastest start-stop repeat frequency). I can not find it in datasheet.

      Pls advice.

     thank you very much!

    Haroad 

  • 0 in reply to Haroad
    TI__Mastermind 31655 points

    Hi Haroad,

    This value is not in the datasheet because it is entirely dependent on the time of flight and the SPI clock speed. A new measurement cannot begin until the measurement registers (TIMEx, CLOCK_COUNTx, and CALIBRATION1 and 2) have been read. Each of these registers is 24 bits. For a single stop, the time to read these registers at max SPI rate is around 5us. On top of this you must add the time of flight (presumable on the order of nanoseconds for LIDAR). The max measurement frequency is the determined by the time of flight + the time it takes to read the registers.


    Regards,