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LDC1612: How to calculate for the required resolution

user6188424
Prodigy 160 points
Part Number: LDC1612

I am confirming that whether the required resolution for the measurement distance is possible　by Using design Excel (LDC_Tools-ext49).

If Required RCOUNT (Dec) is less than 2 ^ 16 (65536 data), the judgment value is OK. I understand it because it is 16bit output.

but I do not understand the meaning of the required RCOUNT (Dec) formula.

Required RCOUNT (Dec) =(10^(LOG(desired resolution /25317/ Reference Frequency,10)/-1.0023)/32)*(1.5*fSENSOR at D1 )

（ΔｆHz/Counts＝ desired resolution [Hz]　　←OK）

Please tell me the reason and outline of the formula to judge whether the design is possible.

I'm sorry for your inconvenience.

  • 0
    TI__Genius 17440 points

    Hello,

    Unfortunately I can't explain that formula because it relies on the internal workings of the LDC1612.

    However, you do not need that formula to determine whether your required resolution is achievable with a given coil design. The tool you mentioned above is a great way to get a recommended RCOUNT setting for your desired resolution, but we recommend calculating your SNR in Hz to determine whether or not your resolution is achievable.

    You can use the Axial Target Movement Calculations section to calculate the SNR. I recommend inputting your farthest target distance, then in the closest target distance cell input this: [ (farthest target distance) - (minimum desired distance resolution) ]. Use the sensor frequency shift as your signal in the SNR calculation.

    You can refer to this e2e question for a recommended method to measure the noise floor. We recommend an SNR of at least 10 for robust sensing. If your SNR is at least 10 for the above calculation, then your resolution is realistic. Please note that the LDC Tools provides estimations, so you may see some differences in your prototypes. These are often due to parasitic inductances and capacitances in the sensor layout that are not accounted for in the excel calculations.

    Best Regards,

  • 0 in reply to Kristin Jones93
    Prodigy 160 points

    Thank you for your prompt reply!

    If Δf (fHz (d2) -fHz (d2-Δd)) is sufficiently large with respect to the noise floor, can it be considered that the resolution is obtained including accuracy?

    Is the idea that the Resolution calculated by Required RCOUNT is electrical resolution without considering accuracy correct?

    I know that I need to evaluate to know the noise floor,but I’m in the review stage, so I would like to make a judgment by design calculation.

    Is the content of the noise floor below?

    1.Noise from other electronic devices and metals

    2. Changes in L and C due to temperature changes

    3. Reference frequency error

    4.Quantization error