FDC2214: FDC2214 detection range using square copper plate sensors

Pan,

Thank you for your inquiry and your interest in TI products.

It is great that you are searching the database of previous threads before submitting an inquiry. It is  a great resource.

Please also consider consulting the three FAQ documents on our E2E landing page.
One FAQ devoted to our FDC2x1y capacitive sensing family.
Another is an FAQ for the FDC1004 device.
The third is an Inductive Sensing FAQ.

They contain comprehensive Q&As, and many links to app notes and tech notes.

The plot you mentioned can also be found in one of our app notes, Capacitive Proximity Sensing Using FDC2x1y (SNOA940A)

It is Figure 4, appearing in Section 3 on page 5.

The text states:
"To characterize the relationship between sensitivity and sensor size, a proximity test was performed with the FDC2214 for various sensors with a human hand acting as the target. The hand starts from far away and gradually approaches the sensor. When the output signal changes by more than the peak-to-peak noise, it is considered a positive detection...."

So the curve's assumption for detection is when the signal is just detectable over the noise. Please try this criterion in your set-up.
The size of your target hasn't been mentioned, so if it is about the same size as your sensor, you could try making it larger.
Other device settings which can also play a role, like RCOUNT, so please try experimenting with those in your system.

Regards,
John