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TDC7200EVM: Multi cycle averaging jumps

Martin van Schaik
Prodigy 30 points
Part Number: TDC7200EVM
Other Parts Discussed in Thread: TDC7200

Hello,

I am using  TDC7200EVM board to compare it's TOF measurements to the ones from our current hardware solution.

When i use multicycle averaging in the TDC7200 with 8 cycle averaging, the results show some unexpected jumps.

The green line is measured using our current hardware, the red line is from the TDC7200, calculated using the formulas from the datasheet.

I would expect both lines to show similair behavior, but the data from the TDC7200 show jumps in time from about 100ns, which is the clockperiod of the clock used (10Mhz).

What can be the cause of this?

  • 0
    TI__Mastermind 31655 points
    Hello Martin,

    What is the scale for the horizontal axis? This is showing the TOF over a period of time?

    Are you reading the values from the TDC7200 only after the INTB goes high to signal the end of the measurement period?

    Regards,
  • 0 in reply to Scott Cummins
    Prodigy 30 points

    Hello Scott,

    The graph indeed shows the TOF over a period of time,  there is approximately 1.5 seconds between measurements. I zoomed in on part of the graph to make the problem more visible.

    After the measurements i first check if INTB has gone low (it goes low after measurements are complete, right?), then i read the different values from the TDC7200 (TIME1, Clock_count1, TIME2, Calibration1 and Calibration2)  to calculate the TOF. I would expect the TOF from the TDC7200 (red line) to look more like the TOF of our current system (green line) so without the jumps..

  • 0 in reply to Martin van Schaik
    TI__Mastermind 31655 points
    Hi Martin,

    Sorry for the delay. Could you please give a bit more information about the setup? Could you save the config file from the GUI and upload it here? Also, do you notice any dependency on the number of multicycle averaging cycles? Finally, how often are you running the measurement?

    The GUI has some limitations as far as USB data update speeds. One thing I would suggest is to decrease the measurement frequency in the setup tab and see if that affects the results.

    Regards,
  • 0 in reply to Scott Cummins
    Prodigy 30 points

    Hi Scott,

    I'm not using the GUI, I have the TDC7200EVM board connected to one of our exisiting measurement systems which measures the TOF using a counter in a PLD. I use the start and stop signals for that counter to also start and stop the TDC7200. Before doing the measurements I first configure the TDC7200, then i start measurements with our own system and let the TDC7200 time them in parallel with the counter in the PLD.

    The configuration of the TDC7200 is:

    CONFIG1: 0x02 (no forced calibration, parity disabled, Rising edges for both triggers, measurement mode 2)

    CONFIG2 : 0xD8 (Calibration2 40 clock cycles, 8 measurement cycles, single stop)

    Before the start of each measurement I write 0x03 to CONFIG1 to start the measurements.

    So far I have only tried 8 cycle averaging, mainly because of the memory limitations of our measurement system.

    I did try doing 10 single measurements with the TDC7200  (so no multi cycle averaging) and storing the TOF after each measurement and averaging the  TOFs after all measurements where complete.

    When doing this I didn't observe any jumps in the TOF.