A Capacitive Sensor Readout IC With Antenna-Integrated Sensor for Proximity Detection in Handheld Mobile Devices

In this letter, a capacitive sensor readout integrated circuit (IC) and a prototype using an inverted-F antenna (IFA) as the capacitive sensor for proximity detection are presented. A unique front-end circuit converts the single-ended sensing capacitance with one electroplate being always grounded into differential signal utilizing correlated double sampling while suppressing the noise of the front-end circuits. The implemented IC shows that with an offset capacitance of
$\text{72}\,\text{pF}$
, a noise floor of
$\text{17}\,\text{fF}$
can be achieved. The IC was designed and fabricated in a
$\text{90}\,\text{nm}$
RF SOI complementary metal-oxide semiconductor (CMOS) switch technology for its possible integration with radio-frequency (RF) antenna tuning switches. The assembled phone mockup prototype demonstrates the capability of the proposed system to detect the proximity of human body parts with high offset capacitance to maintain the RF performance of the antenna for sub-
$3 \text{GHz}$
mobile communication.