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LDC1101: Interaction of multiple sensor coils close to each other

Harald Noack
Prodigy 70 points
Part Number: LDC1101


Hello

I would like to arrange many LDC1101s with the sensor coils in series at a small distance. The coils are approx. 20 mm wide and have a distance of 5 mm between the coils. This means that these sensor coils are magnetically coupled. This can lead to locking of the resonance circuits, which mutually influence the resonance frequencies.
This can be avoided by detuning the resonance frequencies of the neighbouring sensor circuits.

For example, 1 capacitor and then 2 parallel capacitors and then 1 capacitor again 
=> 
fres: 1, 1/sqrt(2), 1 

Does anyone know of a way to make the resonance capacitors switchable in the LDC1101 topology so that it is possible to switch between 1 and 2 capacitors? Is it possible to switch capacitors by n-channel FETs from INA & INB to ground ?
=> 1 capacitor is connected to the coil and 1 is switchable 

I would actually like a circuit with a switchable resonance frequency and no different assembly options.

Thank you for your help!

Kind regards,
Harald


Translated with DeepL.com (free version)

  • 0
    TI__Mastermind 45085 points

    Hi Harald,

    I can think of a couple ways to do this.  

    1. Use an analog switch to open or connect the extra capacitor.  You should look for something with a low Ron to keep additional parasitics minimized.  TI analog switch devices can be found below.

    ti.com/product-category/switches-multiplexers/analog-mux/products.html

    2. Use a digital variable capacitor.  TI does not offer such a product, but there are digital capacitors available where the capacitance can be varied through a digital interface such as I2C.