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TDC7200: TDC7200 calibration

Ross Swanson
Prodigy 120 points
Part Number: TDC7200

Hi,

The data sheet does not describe when calibration is done, I'm interested in mode 2, without averaging enabled. 

1.) When INTB fires low are we guaranteed the registers calibration_1, and calibration_2 are ready to be read? The data sheet does not confirm this.

2) When is the calibration measurement made, just after the time_1 recording is begun, or when config1 register address 0 START_MEAS bit is set?

I currently use the 10 period mode for calibration_2 but I'm interested in exploring the larger 40 period mode because the majority of my system noise appears to be in the cal_2 data, (as expected?).

--Ross

  • 0
    TI__Expert 3450 points

    Hi Ross,

    1) Yes, the registers are ready to be read once INTB goes low. 

    2) Calibration 1 occurs after START_MEAS, just before TRIGG is asserted. 

    Using a longer calibration will capture a longer segment of your clock signal. 

    What is the application, and by noise do you mean variation in cal_2?

    Regards,

    Gabriel

  • 0
    Prodigy 120 points

    Hi,

    Yes jitter noise in clock to TDC.

    Application is digital pulse skew measurement. BTW it would be good if an update were made to the datasheet about this, along with a note discussing the fact that there is some hystersis in the cal_1 measurement that shows up with time_1 values larger than cal_1 by significant amount that I discussed awhile back with another collegue of yours on this same forum, he dismissed my findings because he could not reproduce them in your demo board. But I see them every day, refer to previous post about this, for example below I'm sweeping a pulse across the TDC input clock and I see these results for time_1 cal_1 cal_2 with period count of 10 (hex)

    time_1 cal_1 cal_2 
    0692 006bd 04354 

    06a4 006bf 0435f
    06b5 006be 04361
    06c7 006bf 04360
    06d6 006bd 04353
    06e9 006be 0435f
    06fa 006be 0435f
    070c 006bf 04365
    071e 006bf 04368
    0072 006be 0435c
    0083 006c0 04369
    0094 006be 0435f
    00a6 006bf 04364

    As you can see the time_1 value exceeds the cal_1 value at 5 locations! It would be good if TI fixed or at least characterized this in the data sheet.

    Thanks,

    --Ross