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Original question:

BOOSTXL-PGA460: Short range measurements

BOOSTXL-PGA460: monitoring PGA460 using oscilloscope

Zeinab Ramshani
Prodigy 70 points
Part Number: BOOSTXL-PGA460
Other Parts Discussed in Thread: PGA460

Hi,

I am using BOOSTXL-PGA460 and I would like to monitor the burst and echo signals using Oscilloscope. I connected the RTRN pin in daughter card to my oscilloscope ,now I can see the burst signal but not the echo. is there any way to see that also? although, the device can recognize the target perfectly and the measured distance shown by the EVM software is correct.

the target is close so considering the 100usec, shown in the snapshot, I must have seen the echo also.

 Thanks,

  • 0
    TI__Expert 7966 points

    Hello Zeinab,

     

    Thank you for your question.

     

    The RTRN pin of the daughter card contains the signal for the ultrasonic burst and echo signal in a mono-static configuration. Often times, the return echo is such a small magnitude that it is nearly impossible to discern the echo from the noise of the system. The PGA460 uses multiple stages of filtering and amplification to enhance the resolution of the return echo, enabling the TOF to be measured. Therefore, I would not expect to be able to see the return signal from the RTRN pin of the EVM.

    Fortunately, there are other ways to evaluate the return signal. One way can be through the EVM GUI, and another is through the Test mode (section 7.3.7.2 of PGA460 Datasheet). In this mode, the user can select various stages in the analog signal path to analyze, see DP_MUX below. Using this mode, you will be able to select a stage where the echo signal is more easily measured on an oscilloscope.

     

    Please let me know if you have any questions, or require help enabling the test mode of the PGA460.

    Thank you,

    Jacob

  • 0 in reply to Jacob Nogaj
    Prodigy 70 points

    Thanks Jacob, I will try to catch it via Test mode. meanwhile I was wondering if you have any advice for increasing the resolution of my system. I am using BOOSTXL-PGA460 with a 300kHZ close top transducer in a transformer driven  monostatic mode for close distance. theoretically the resolution must be in sub mm (1/f), but I get it around 2-3 mm. 

  • 0 in reply to Zeinab Ramshani
    TI__Expert 7966 points

    Hello Zeinab,

    It can sometimes be difficult to improve the resolution for sensing in a monostatic configuration. Filter settings, amplification stages, and general device configuration can all impact resolution in a combined manner.

    Before going into the methods for improving resolution, it can be very effective to look at various Vout waveforms and understand where the varied TOF may be coming from. Some level of variance will always exist in a TOF measurement, but looking the echo data can sometimes help to see where to make changes.

    One method to improve resolution can be through increasing the pulse count, but a drawback will be the decreased minimum sensing distance due to the increased time for the transducer to ring down. Additionally, the increase in pulse count can approach a point where there is no measurable benefit to resolution. Another option can be in altering the thresholding or the gain settings of the PGA460. One method could be in making the threshold higher in value to ensure only a very strong consistent return signal is considered in the TOF calculation. Alternatively, you could also lower the threshold to be sensitive enough to qualify the very start of the return echo in the TOF measurement. Ultimately it is like most settings, being a balance between the two for an optimal system. Finally, another method for improving resolution is to ensure the target and the transducer are positioned parallel to one another. This can improve the consistency of the return echo as the echo will be uniform in the direction of travel.

    I wish there were an easier solution to guarantee an improvement in resolution, but the tuning of parameters is characteristic of ultrasonic sensing applications.

     

    I am always happy to look at waveforms and give recommendations as for where to make alterations.

    Please let me know if you have any questions.

    Regards,

    Jacob