A Sensing Mode Reconfigurable Analog Front-End IC for Capacitive Touch and a-IGZO TFT-Based Active-Matrix Capacitive Fingerprint Sensors

In this paper, we propose a sensing mode reconfigurable analog front-end (AFE) IC for a capacitive touch sensor (CTS) and amorphous indium-gallium-zinc-oxide (a-IGZO) thin-film transistor (TFT)-based active-matrix capacitive fingerprint sensor (CFS). The CTS consists of the transmit and receive electrodes for enabling the mutual-capacitance (C
_M
) sensing mode, which can detect the multi-touch. The CFS has the array of a-IGZO TFT and a sensing electrode for enabling the self-capacitance (C
_S
) sensing mode to achieve the high sensitivity. In addition, it can reduce the number of sensing lines by adopting the active-matrix type structure to achieve the low-manufacturing cost. To sense the CTS and CFS, the proposed AFE IC is reconfigured to operate the C
_M
and C
_S
sensing modes, respectively. The proposed AFE IC was fabricated using a
$0.13~\mu \text{m}$
CMOS process technology with 20 V high-voltage devices, and demonstrated with a
$128\times 72\,\,32$
-inch CTS and a
$96\times 96\,\,0.27$
-inch CFS, which represents a pixel resolution of 500 pixel-per-inch. The proposed AFE IC achieves the signal-to-noise ratios of 47.8 dB and 25.0 dB for the CTS and CFS, respectively.