LDC1000 linear measurement with rectangular coil design

Hello Matin,

The sensing range will be detrmined by the narrow side of the rectangle. Thus, if the distance between the sensor and the target is 3-5mm, the narrow outer diameter of the rectange should be at least 10mm. Also, please consider having spacing in the x-direction larger than the one in y-direction as shown in the fugure below.

You can approximate the inductance of the sensor by using narrow radius of the circular coil radius.  

 

Hi Natallia,

thanks for this fast information.
I will make a PCB layout with this kind of shape and test it in my application.
Will that use case be implemented in WEBBENCH in near future?

Yours sincerely

Hello Martin,

The feature above is very useful for Webench. However, it will take some time to release it. What layout SW are you using? You could write a vb script to place your coils in Altium.

Best Regards,
Natallia Holubeva

Hi Natallia,

I'm using TARGET3001 from ibf. This software doesn't support scripts.
I hope the linear measuring feature will be released sometimes in WEBBENCH.

Yours sincerely

Hello Martin,

I would be happy to put a request for you. If you are trying to approximate the inductance of a rectangular coil, please use the narrow radius and approximate it to the circular coil. Physically, it is the area that matters the most but I noticed you get the closest result while approximating with the narrow radius of the rectangle.

Best Regards,

Natallia Holubeva  

Hi Natallia,

I try to approximate the inductance of the rectangular coil with the narrow radius. I hope it will works.

Yours sincerely

Martin,

Great. You could also list the foloowing parameters and I can approximate it for you:

1. Number of turns

2. Radius

3. Trace space and trace width

4. Number of layers.

 

Best Regards,

Natallia Holubeva

Hi Natallia,

sorry for the late reply. I had a short vacation.

Now to the parameters:

1. 30 turns
2. 6mm radius (the smaller one)
3. 0.1mm trace space and trace width
4. 2 layers (FR4 1.0mm)

Yours sincerely

Hello Martin,

Do you mean 30 turns per layer? If so, its not quite possible with 4x4 trace and space width (0.1 mm ~= 4 mil). You need space in between for the via. With 15 turns per layer, the spiral approximation is 10.674 uH, which is great! With 200pF cap in parallel, you will get Rp = 8.3k, quality factor of 19, F sensor = 3.4MHz, and self resonance frequency of the coil = 21.8MHz. All satisfy the datasheet.

Best Regards,
Natallia Holubeva