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Original question:

LDC1614EVM: LDC1614 shows up as LDC1314

LDC1614: avoiding interference from fourth layer

eveblaw
Prodigy 90 points
Part Number: LDC1614

Hello,

I have a four layer PCB on which I placed a two-layer PCB coil design on the top two layers. It needs to measure the distance to a piece of metal above the pcb, anything below the coil should not have any impact on it.

My problem is that I need to route a trace on the fourth (bottom) layer under the PCB coil. Obviously, this is giving me a lot of noise on the measured inductance. Could I do something like a ground plane on the third layer to remove this noise? Could I make use of chapter 2.1.2 from the document below, or is this meant for other situations? Are there other things I could take into consideration for the design to make this work?

The document: http://www.ti.com/lit/an/snoa962/snoa962.pdf

I look forward to hearing from you!

  • 0
    TI__Genius 14270 points
    Hello,

    Can you show your routing? While putting traces on layers below a sensor is undesired, you may be able to minimize the effect by using a thinner trace, avoiding loops around the the center of the sensor, using a thicker PCB stackup, and making sure any signals on the trace are low amplitude and not close to the sensor frequency. Have you checked your sensor IDRIVE setting to make sure it is within the optimum range of 1.2Vp to 1.8Vp?

    Regards,

    ChrisO
  • 0 in reply to Chris Oberhauser66
    Prodigy 90 points

    Hey Chris!

    Below you will find a screenshot that portrays the problem I am having. The coil is on layer 1 and 2. The trace that is going from the left side to the right side on the lower part of the coil of the board is on layer 4. The purple lines are the outline of the PCB. Could I place anything on layer three to lower the effect of this trace on layer 4?

    Disclaimer: This is an older pcb design. The coil isn't perfectly spiral and the capacitor placement is not optimal.

    https://i.imgur.com/g72IzEA.png

  • 0 in reply to eveblaw
    TI__Genius 14270 points
    Hello,

    I don't think the problem is that trace. You could check that by cutting the trace on one board and assessing the effect - since that trace is on the top layer, you should be able to get to it with an exacto knife.

    What is sensor diameter, the target distance, and the target material?

    Can you provide an oscilloscope trace of the INxA/INxB signals?

    Regards,

    ChrisO
  • 0
    TI__Intellectual 1020 points
    Hello

    I will be closing this thread as we've not heard from you in the past couple of weeks. If you have more questions, please ask a new question or ask a related question.

    Regards,

    Vaibhav