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TDC7200: Question of understanding regarding multi-cycle averaging

Felix Mullis
Prodigy 20 points
Part Number: TDC7200

In the Multi-Cycle Averaging Mode, the TDC7200 performs a series of measurements on its own. Is it correct that this mode only affects the CLOCK Counter Values and not the Measured Time Values? When I increase the AVG_CYCLES value, the CLOCK Counter Values increases proportional, but the Measured Time Values do not increase. It looks like the Measured Time Values are always single measurements. Can you confirm that?

Thanks a lot.

Felix Mullis

  • 0
    TI__Mastermind 27780 points

    Hi Felix,

    All Measurement Result registers are influenced by multi-cycle averaging mode and used in the TOF equation as described in the datasheet:

    "The results of all measurements are reported in the Measurement Results registers (TIME1 to TIME6, CLOCK_COUNT1 to CLOCK_COUNT5, CALIBRATION1, CALIBRATION2 registers). The CLOCK_COUNTn registers should be right shifted by the log2(AVG_CYCLES) before calculating the time-of-flight (TOF). For example, if using the multi-cycle averaging mode, Equation 2 should be rewritten as: TOFn = normLSB [TIME1 - TIME(n+1)] + [CLOCK_COUNTn >> log 2 (AVG_CYCLES)] x [CLOCKperiod]"

    The CLOCK counter value increases due to the log2(AVG_CYCLES) shift function. After the multi-cycle averaging is complete, are you observing no change in the TIMEn values regardless the number of average cycles (1 vs 128)? Are you only reading these values after the averaging cycle is complete (INTB interrupt trigger indicates completion)?

  • 0 in reply to Akeem Whitehead
    Prodigy 20 points

    Hi Akeem,

    I read all the result values after the averaging cycle is complete. The CLOCK counter value increases due to the log2(AVG_CYCLES) shift function, but not the TIMEn values. This different behaviour is the reason of my question. For the TOF calculation, it is necessary to adjust the CLOCK counter values but not the TIMEn values. From this fact, I conclude that the TIMEn value is either already the mean value of all the single measurement values or just a single measurement value (probably the one from the last cycle). If it is the mean value, then the right shifting by the log2(AVG_CYCLES) must be done by the TDC7200 and I think that is not the case.

    So I'm looking for the definition and specification respectively of the TIMEn register values in the Multi-Cycle Averaging Mode. I hope you can provide me some more details and information regarding this register values.

    Thanks again

    Felix 

  • 0 in reply to Felix Mullis
    TI__Mastermind 27780 points

    Hi Felix,

    The TIMEn value is already the mean value of all the single measurements after the number of measurement cycles has been matched. The log2(AVG_CYCLES) compensation is performed at the master controller (not TDC7200) to compute the time-of-flight as shown in the previously mentioned equation-2 explanation.