FDC2214EVM: I would like to ask about the coils mounted on the evaluation board.

Hello Masato,

Thank you for your patience while we were out for the Thanksgiving holiday.

I believe that the components are only located on one side of the EVM for two reasons: lower cost of assembly and ease of probing signals.

You could definitely have different sensor channels mounted on the front and back of the board. You don't need to add a GND plane in between, because when the channels are not actively being measured they are shorted to GND. Only one channel can be measured at a time, so they cannot interfere with one another. In fact, I do not recommend placing a ground layer in between your sensors, because this could decrease the sensitivity to the target. 

It's definitely possible to use smaller inductors than those we've used on the EVM. I do recommend using shielded inductors to reduce EMI, but the value and the package size of the inductors are very flexible. Just make sure that your sensor frequency is within the datasheet specifications (1kHz to 10MHz) and that your sensor oscillation amplitude is between 1.2V - 1.8V for the whole range of target movement. Though written for inductive sensing, this application note also provides information about setting the drive current for FDC2xxx devices.

Best Regards,

Hello, Kristin

Thank you for answering kindly.

You could definitely have different sensor channels mounted on the front and back of the board.

→include components?(coil & capacitor etc)　there is coil on front side and capcitor on back side , OK?

Best Regards,

Masato

Hello Masato,

I recommend keeping the LC tank on the same side of the board if possible, but it should still work if you place them on opposite sides of the board. The inductor and capacitor should be placed as close to each other and as close to the FDC device as possible.

Best Regards,

Hello! Kristin,

Thank you for replying.

I recommend keeping the LC tank on the same side of the board if possible, but it should still work if you place them on opposite sides of the board. The inductor and capacitor should be placed as close to each other and as close to the FDC device as possible.

→

I understand.

Is there anything else to be aware of?
(Grounding of the LC tank part, etc. (Since the response to the sensor part is poor, I heard before that GND is not necessary))

　Best Regards,

 Masato

Hello Kristin,

My explanation was insufficient.

Is it not necessary to shield the LC tank by filling it in with solid GND instead of short-circuiting the LC tank? about it.

However, as long as the layout of the data sheet is checked, it seems that the LC tank and sensor are not filled or the GND layer is not below. .

Is it correct in the interpretation that if there is a GND layer around the LC tank and the sensor part, the reaction will worsen?

I thought it would be better to put GND for each channel,

Example)

IN3B IN3A | GND | IN2B IN2A | GND | ・ ・ ・

Best Regards,

Masato

Hello Masato,

You are correct, you should not use a GND pour around the sensors nor directly below the sensors on any layer. This will create a large sensor capacitance to GND, which will make the sensor less sensitive to the desired target.

Best Regards,

Hello Kristin,

I attached the materials.
please confirm.
Do not place GND on the front and back sides of the pink area of ​​the FDC board and on the inner layer.

Is it correct that the sensor board side indicated in the document does not require GND on the front and back sides?

I understand that the sensitivity decreases when GND is present.
Is interference between adjacent channels all right?
(1ch responds even though 0ch is touched.)

Best Regards,

Masato20191210_board image.pdf

Hello Masato,

Yes, your keepout areas in the image you attached are correct. It's not surprising that you may have some crosstalk if your electrodes are located very close together. You could try reducing the size of the electrode to reduce its sensing range. 

Best Regards,