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FDC2214EVM: near field proximity sense resolution @ max data rate

stefan kubina
Prodigy 20 points
Part Number: FDC2214EVM
Other Parts Discussed in Thread: FDC2114, FDC2214, FDC2114EVM

Hello

I'm trying to find the maximal resolution and maximal data output rate (single Channel)

for a near field (4 to 0,2 mm,  Captive Sensor Surface about 300 to 400 mm²)  distance / proximity sensing application, by evaluating the FDC2214EVM with Sensing Solution EVM GUI V1.10.0 .

I've been using following settings:

When approaching the sensor plate with my hand,

I only get a raw value change of roughly 300dec counts,

but the frequency changes about 400.000 Hz!

- hand gone, raw code = 1000, hand touching the sensor plate, raw code =~ 700   OR

- hand gone, capacity = 54.3 pF (5087 kHz) , hand touching the sensor plate, raw code =~ 65 pF (about 4680 kHz)

How can the resolution for this given Captive Sensor Surface be maximized?

  • 0
    TI__Genius 17440 points

    Hi Stefan, 

    You mentioned the FDC2214EVM in your description, which is our highest resolution capacitive sensing device. But you are actually using the FDC2114EVM, which has 12 bits of resolution. You can tell by looking at the black bar at the bottom of the GUI. The FDC2114 has much smaller raw output code values than the FDC2214, which may be why the 300 code shift looked wrong to you.

    If you would like to continue using the FDC2114, it has gain and offset options to maximize its resolution. Section 9.3.2.1 of the datasheet discusses ways to use these options. 

    If you would like to use the FDC2214EVM, please double-check your order receipt. If there was a shipment error please seek help through this channel. If there was no shipment error you may need to order a new FDC2214EVM.

    You may also find this proximity sensor EVM helpful. It uses the FDC2214, which is a higher resolution (28 bits instead of 12 bits). 

    Best Regards,

  • 0 in reply to Kristin Jones93
    Prodigy 20 points

    Hello Kristin,

    Thank you for your prompt reply!

    I picked the FDC211x EVM because of it's high output data rate. (sorry for the number swap in the title)

    I 'd like to understand what to do, to get an output closed to the 12 bit (4095 dec) resolution for the near field distance (0,2 to 4 mm) sensing?

    Since currently I can't manage to get more than roughly 8bit resolution for roughly 0 to 15 mm range.

    kind regards

    Stefan

  • 0 in reply to stefan kubina
    TI__Genius 17440 points

    Hi Stefan,

    From a device configuration perspective, you want to use a high offset value and the maximum gain setting possible without saturating the measured data. Ensure that your data offset is not larger than the raw code value without any offset applied. It looks like you are using this approach already in the GUI screenshot you shared. 

    From a sensor design perspective, larger sensors can be more sensitive than smaller sensors (though this effect has diminishing returns as the sensor becomes larger than the target). Grounding your target will also increase the capacitive response, though it sounds like your target will be a human and this is not an option for your application. 

    You likely will not be able to create a system that utilizes the full scale range of the output codes. Keep in mind that even with a gain of 4 (which minimizes the full scale range of the output codes), the full scale range of the output codes equates to a sensor frequency shift of almost 2.5MHz. This is unreasonable for almost all capacitive sensing applications. 

    Instead of focusing on the full scale output range, maximize your SNR. We recommend an SNR of at least 10 across your full range of motion for robust sensing. You can measure your peak-to-peak noise using the "Show Statistics" button on the Data Streaming tab of the GUI.

    Best Regards,