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PGA460: Long Range Detection and Noise Level

Part Number: PGA460

Hi,

I recently designed a custom board based on PGA460, but detecting obstacles in the short-range up to 7 meters is good but for further it can't measure anything except noise. the excitation frequency is 74khz, I checked this frequency with BOOSTXLPGA460 and it was working perfectly and it could detect obstacle up to 10.5 meters which is great for my application. also, I noticed that the noise level is between 25 and 44 based on pga460evm GUI.

it would be great if you guide me through this issue to fix this problem.

  • Hi EngineerPlus,

    Were you able to resolve the amplitude difference observed from your last post at https://e2e.ti.com/support/sensors/f/1023/t/909741 ?

    If you are still seeing a difference in the amplitude of the BOOSTXL-PGA460's VOUT output versus your custom board's VOUT signal, then you still may have a configuration issue with your time varying gain range. Ensure all of your register settings are identical to rule out the possibility of a register setting issue.

    If your register values match, then be sure to check the driver stage as I mentioned on your previous post:

    Driver stage: probe the OUTA, OUTB, transformer's primary center-tap, and XDCR's secondary voltage. If these signals match the EVM, then the driver stage is good, and the transducer should be generating sufficient sound pressure level.

    Until the analog driver and receiver signal match, you will not be able to up to 10.5 meters on your custom board because it's amplitudes are currently weaker than the EVM's.

    Can you share a copy of your custom board's schematic for review?

  • Hi Akeem,

    Yes, the previous issue got fixed. I've just put some wrong value capacitor on the INN pin (it was around 3.3pF). But actually I didn't measure the test pin output after that. now the condition is better and I can measure up to 6.5-7 meters with init gain 66 and digital gain x2 for short-range. Now I have a problem with measuring further than 7 meters. actually, after TH9 is the problem, it doesn't measure anything with x2 and with x4 it doesn't show anything except noise even in a wide area without any obstacle in front of it.

    according to your suggestion, I just detached the FB1 and put some wire instead of it.

  • Hi EngineerPlus,,

    If you move the TH9 point in time to sit beyond 10.5m, are you then able to see objects between 6.5-10m?

    It sounds like an issue is either:

    • the long range digital gain value is not set as expected because the long range digital gain takes effect at TH9 and beyond. One way to check this is to set the long rang digital gain to x1 and then x32. The noise floor should beyond TH9 should rise significantly, even without an object. Note, there are two digital gain multiplier settings, one for preset 1 and another for preset 2. Be sure you are not setting preset 1's digital gain, but using a preset 2 burst/listen command.
    • you are reading the echo data dump too soon, and are not allowing the PGA460 to capture the echo activity past ~36ms. 36ms in distance is about 6.3m. For a 10.5m maximum, be sure to wait 62ms between your burst/listen command and the echo data dump read command to allow the echo data dump to fill completely. In this scenario, I assume you are not using the GUI, because this GUI already incorporates the proper amount of delay between commands.

  • Hi Akeem,

    Saturation of the LR is good and occurs when the gain is too much. but with medium digital gain around 4-2 it shows noisy plot and with gain 1 it doesn't detect anything. In addition, I have enabled DSP Non-Linear Scaling, could it be trouble in this case?

    actually I tested with both, my firmware and the GUI. same result with both! on my firmware, I read the result every 500ms.

    I will test changing the time of TH9 to beyond 10m tomorrow and I will inform you.

  • Hi EngineerPlus,

    For the purpose of debug, I recommend that you disable the Non-Linear Scaling feature.

    If you already have sufficient delay (500ms), then it is likely a DSP issue (either due to the digital gain multiplier or non-linear scaling).

    Let's see how if moving the TH9 point further in time helps - you can keep me updated.

  • Hi Akeem,

    I performed the test. and set the TH9 to about 10.5m. the echo data dump is really weird.

    I disabled the Non-Linear Scale and set the Digital Gain for short-range to x32 and this is what I saw on the GUI.

    the up Threshold is TH9.

    I also performed a test with Digital Gain x4 and Disabled Non-Linear Scale and set TH9 as you can see in the plot but unfortunately, I couldn't see any peak on the plot even around 9 meters.

  • EngineerPlus,

    Can you send me a copy of your GUI's Memory Map register value text export file? I'd like to review your latest settings, and try running the setup on my EVM.

    Based on your echo data dump output, your time varying gain appears to be ramping up very quickly to a large dB value, which is why the echo data dump signal appears saturated. You may need to reduce your time varying gain levels to prevent saturation.

  • Akeem,

    Actually I increased the digital gain and TVG intentionally, to see the saturation. If you look at the plot around the 9.5 meter and beyond the signal get low and its odd. It Looks like the tvg or digital gain isn't working properly after 9 meter

    I will send the register map for you by the tomorrow.

    Thanks

  • Hi Akeem,

    this is the register map that I use.

    test.txt
    ;GRID_USER_MEMSPACE
    00 (USER_DATA1),00
    01 (USER_DATA2),00
    02 (USER_DATA3),00
    03 (USER_DATA4),00
    04 (USER_DATA5),00
    05 (USER_DATA6),00
    06 (USER_DATA7),00
    07 (USER_DATA8),00
    08 (USER_DATA9),00
    09 (USER_DATA10),00
    0A (USER_DATA11),00
    0B (USER_DATA12),00
    0C (USER_DATA13),00
    0D (USER_DATA14),00
    0E (USER_DATA15),00
    0F (USER_DATA16),00
    10 (USER_DATA17),00
    11 (USER_DATA18),00
    12 (USER_DATA19),00
    13 (USER_DATA20),00
    14 (TVGAIN0),FF
    15 (TVGAIN1),FF
    16 (TVGAIN2),FF
    17 (TVGAIN3),5D
    18 (TVGAIN4),B7
    19 (TVGAIN5),5F
    1A (TVGAIN6),94
    1B (INIT_GAIN),0F
    1C (FREQUENCY),DD
    1D (DEADTIME),F0
    1E (PULSE_P1),01
    1F (PULSE_P2),14
    20 (CURR_LIM_P1),47
    21 (CURR_LIM_P2),3F
    22 (REC_LENGTH),1F
    23 (FREQ_DIAG),00
    24 (SAT_FDIAG_TH),EE
    25 (FVOLT_DEC),7C
    26 (DECPL_TEMP),0F
    27 (DSP_SCALE),CC
    28 (TEMP_TRIM),00
    29 (P1_GAIN_CTRL),00
    2A (P2_GAIN_CTRL),02
    2B (EE_CRC),F3
    40 (EE_CNTRL),00
    41 (BPF_A2_MSB),8E
    42 (BPF_A2_LSB),5F
    43 (BPF_A3_MSB),FC
    44 (BPF_A3_LSB),CE
    45 (BPF_B1_MSB),01
    46 (BPF_B1_LSB),99
    47 (LPF_A2_MSB),7F
    48 (LPF_A2_LSB),33
    49 (LPF_B1_MSB),00
    4A (LPF_B1_LSB),67
    4B (TEST_MUX),00
    4C (DEV_STAT0),80
    4D (DEV_STAT1),00
    5F (P1_THR_0),FF
    60 (P1_THR_1),FF
    61 (P1_THR_2),FF
    62 (P1_THR_3),FF
    63 (P1_THR_4),FF
    64 (P1_THR_5),FF
    65 (P1_THR_6),73
    66 (P1_THR_7),9C
    67 (P1_THR_8),E7
    68 (P1_THR_9),39
    69 (P1_THR_10),CE
    6A (P1_THR_11),70
    6B (P1_THR_12),70
    6C (P1_THR_13),70
    6D (P1_THR_14),70
    6E (P1_THR_15),00
    6F (P2_THR_0),FF
    70 (P2_THR_1),FF
    71 (P2_THR_2),FF
    72 (P2_THR_3),FF
    73 (P2_THR_4),FF
    74 (P2_THR_5),FF
    75 (P2_THR_6),73
    76 (P2_THR_7),9C
    77 (P2_THR_8),E7
    78 (P2_THR_9),39
    79 (P2_THR_10),CE
    7A (P2_THR_11),70
    7B (P2_THR_12),70
    7C (P2_THR_13),70
    7D (P2_THR_14),70
    7E (P2_THR_15),00
    7F (THR_CRC),0C
    EOF
    

  • Hi EngineerPlus,

    I loaded your memory map file into the GUI, and see no issue when running your settings on the BOOSTXL-PGA460 EVM. This confirms that your settings are valid. Based on your previous comments, you are also able to successfully able to run this configuration on the BOOSTXL-PGA460 EVM, so this issue must be related to your custom hardware.

    On your hardware, are you able to probe the following?

    During the burst-and-listen record cycle, oscilloscope probe:

    • VPWR pin to ensure it does not drop below 6V during the burst-and-listen. If it does, it may be causing an undervoltage condition, which will result in random behavior or device reset.
    • the AVDD pin to ensure analog regulator is maintaining a voltage of 1.8V throughout the burst-and-listen record cycle
    • the IOREG pin to ensure the digital interface regulator is maintaining a voltage of 5V (since your TEST pin is pulled high) throughout the record cycle

    Also, perform a complete read of all registers before and after the first burst-listen command to see if any settings changes during the burst-listen record cycle.

    An additional hardware changes to consider:

    • Replace the F2 fuse with a 0Ohm short.
  • Hi Akeem,

    I scoped the VPWR and it was 11.9v 

    on AVDD it was 1.74v

    on IOREG it was 11.5v

    all voltages were steady.

    actually I desoldered the pull-up resistor on test pin to use 3.3v logic level.

    VPWR

    AVDD

    IOREG

    DECPL

    on DECPL pin scoped some pulses with varying values. is it ok?

    According to what you said, the voltage on IOREG is odd.

  • Hi EngineerPlus,

    All of your voltages are correct, other than the "IOREG". Are you sure you didn't probe the "IO" pin? IOREG should be 3.3V if TEST is floating, or 5V if TEST is resistor pulled up to 3.3V or 5V. If IOREG is 11V, then the IOREG is damaged, and your communication would be failing. The IO pin will be ~11V when VPWR is ~12V (drop occurs due to internal diode drop). Please verify if IOREG pin is actually 3.3V or 11V.

    The DECPL pin functionality is OK because you have the decouple option running in the time decouple mode, which will toggle once between each burst/listen command.

  • Hi Akeem,

    You were right, it was my mistake! that plot was for "IO PIN". I scoped the "IOREG" pin and it was 3.28v.

    And the problem still exists.

    Weak signal return and also not detecting further than 6~7 meter...

  • Hi EngineerPlus,

    Thanks for confirming the IOREG voltage. All the regulator voltages are good, so there is no reason communication or AFE performance would fail during the burst/listen command.

    Have you tested if the same problem occurs on more than one device? I wonder if it is just this single device that is defective. The fact that the settings work on the EVM, but not your custom board leads me to believe that your custom board's PGA460 may be damaged. Alternatively, if you are able to swap the PGA460 ICs, this will help confirm if the problem is IC related, board related, or register related.

  • Hi Akeem,

    thanks for your suggestion. Actually I've changed the IC but still have the same problem. I faced something on the oscilloscope:

    On center-tap I see voltage got a bit decreased. Could it be the problem? (Blue: Center tap  Yellow: OUTA)

    But on EVM this voltage decrement on center tap didn't happen.

    EVAL Board  Blue: OutA   Yellow: center tap

    there is also another question, is it important to use ENIG as a surface finish?

    another question is, is it important to exactly match the impedance on traces with Piezoelectric and the connected wire to it?

  • EngineerPlus,

    Since you swapped the PGA460 IC with a new device on your custom hardware board, and the same problem exists, the issue does seem to be related to your custom hardware board. The transducer burst signal and center-tap voltages you've probed appear correct. The center-tap voltage is expected to droop slightly during burst, so what you've observed is normal. As long as the center-tap voltage does not drop below 5V, the PGA460 will not enter an under voltage state.

    I do not think an ENIG surface finish is critical. Also, the trace impedance does not need to exactly match the piezoelectric and/or wires either. I have had success using the PGA460 in a wide variety of connection schemes (i.e. jumper wire, breadboard, various PCB trace widths, etc.).

    At this point, you may need to perform a detailed probe debug/analysis of each PGA460 pin on your custom hardware and compare the oscilloscope activity of each pin to the working EVM solution. Also, are you able to take the initial PGA460 unit you removed from your custom board, and populate it onto the EVM? This will allow you to check if the PGA460 IC is becoming permanently damaged on your custom hardware.

  • Hi Akeem,

    Thanks for your suggestion, I'll do changing the IC of EVM with one of my own IC's.  Removing the PGA of EVM won't damage the EVM or its IC?

  • EngineerPlus,

    Removing the PGA460 from the BOOSTXL-PGA460 board will not cause damage as long as you are careful.