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Max frame rate of TI TOF sensor

Andrei Talapov
Prodigy 60 points
Other Parts Discussed in Thread: OPT8241, OPT9221

My potential application of TI TOF sensor requires very high frame rate.

I used OPT8241-CDK-EVM with Voxel Viewer.

To get high frame rate I started with No Calibration Profile in Voxel Viewer, which automatically set

dealias_en=False, mod_freq1=48MHz and quad_cnt_max=4.

I changed sub_frame_cnt_max to value of 1.

To decrease readout time, I set ROI to 320 by 1.

Then voxel Viewer changed Video Mode to 120 fps.

After that I manually increased fps until Voxel Viewer showed Error “Failed to set frame rate at 241.00fps” and crashed.

What is the reason for limiting fps to 240?

By the way, the real frame rate was not 240 fps but 200 fps, as can be seen on the attached oscillogram of emitted laser light.


  • 0
    TI__Genius 14835 points
    For laser safety compliance, on the OPT8241-CDK-EVM, we restrict the lower limit of pix_cnt_max to 50000. This corresponds to a maximum frame rate of 240fps (given by (SYS_CLK_FREQ / (QUAD_CNT_MAX * SUB_FRAME_CNT_MAX * PIX_CNT_MAX)) == 48e6/(4*1*50000)).

    Your measured frame rate is probably 200 because the last successful pix_cnt_max setting was for a value of 60000. Could you check if this is the case?
  • 0 in reply to Anand Gadiyar
    Prodigy 60 points

    Anand,

    Voxel Viewer claims pix_count_max=50000 and  240 fps, while oscilloscope shows 200 Hz frequency.

    I wonder how 240 fps limit is related to laser safety. I see that the max laser signal is exactly the same as in all other regimes of operation, and averaged laser power  is not high because here I used default 14% duty cycle.

    What is the meaning of pix_cnt_max parameter? Lowest value of 50000 is definitely lower than total number of sensor pixels 76800.

    From the attached figure it is clear that time from start of exposure for one full frame to the end of exposure ( from start of the first quad to end of the 4th quad) is less than 4 ms.

    For my possible application it would be very desirable to decrease this time for a minimum.

    SBAS703a mentions parameter lumped_dead_time which supposedly should do this. But I could not find it in Voxel Viewer.

    What happened to it?

  • 0 in reply to Andrei Talapov
    TI__Genius 14835 points
    Andrei,

    VoxelSDK shows 240fps because you attempted to set it, and that setting did not go through. The actual setting is what you read back for the 50000 pix_cnt_max.

    The pix_cnt_max value is the quad time in cycles of the 48 MHz system clock.
    (refer to section 7.3.3 of SBAS703A).


    We have the following restrictions in the CDK-OPT8241-EVM.
    - PIX_CNT_MAX lower limit of 50000
    - INTG_DUTY_CYCLE upper limit of 20
    - LUMPED_DEAD_TIME disabled
    - ILLUM_DC_CORR* disabled

    This is enforced in the SDK and in the FX2 firmware and only for the CDK-OPT8241-EVM for laser safety.
    github.com/.../TintinCDKCamera.cpp

    Designs you build with the OPT8241+OPT9221 chipset need not have this restriction.

    We limited these on the CDK because a combination of deliberate/accidental settings (for example a very high frame rate plus high integration duty cycle) could potentially be unsafe.
  • 0 in reply to Anand Gadiyar
    Prodigy 60 points
    Anand,
    I compared distance measurement noise of OPT8241-CDK-EVM with distance measurement noise of ESPROS DME600 TOF camera and found TI sensor noise to be several times lower. This looks encouraging. But to know if it is worth to continue testing TI sensor, it would be very useful to know what minimal one frame exposure time (from start of first quad to end of last quad in frame) can be achieved. It also would be of great value to know what maximum frame rate can be achieved for the small ROI of size 320*1. Is it true that such values only can be found if I will write my own SDK and FX2 firmware?