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LDC1612: sensor layout across stack

avi nevo
Prodigy 10 points
Part Number: LDC1612

I am using 6 layers, 1 oz, 2 mm PCB and would like to design a 7mm diameter sensor. 

I noticed that web tools are capable to export PCB files to a maximum of 4 layers designs. 

 

From performance and resolution aspects - is it better to design 6 layers sensor or 4 layers sensor assuming diameter is kept 

constant? 

if I would like to avoid the external influence of metal that are not the target : 

- is it better to spread the 4 layers sensor design across 6 layers, leaving 2 unused layers in the middle of the PCB or

is it better to use 4 layers sensor located close to the target side, leaving 2 empty layers?

thanks 

  • +1
    TI__Genius 17670 points

    Hello, 

    You will get better frequency resolution using the 6 layer design. This increases the inductance and decreases the frequency compared to the 4 layer design. You can modify the 4 layer output to include the extra 2 layers, just be careful of the coil direction when adding the extra layers. 

    Also, have you seen the Optimizing L Measurement Resolution for the LDC161x and LDC1101. Figure 5 specifically shows the relationship between coil frequency and resolution. 

    Resolution aside, if you run a 4 layer design, you can add shielding on the bottom if you do have concerns for external influences from the opposite side of the target. The EMI Considerations for Inductive Sensing app note has more information on shielding. If you do run the 4 layer design, it is best to put it on the side closest to the target and leave the last 2 layers empty. 

    Best Regards, 

    Justin Beigel