26.3 A 45.8dB-SNR 120fps 100pF-Load Self-Capacitance Touch-Screen Controller with Enhanced In-Band Common Noise Immunity Using Noise Antenna Reference

In capacitive touch systems, high SNR self-capacitance sensing has been mostly used for the following purposes: (1) to realize multi-touch on the matrix sensor, especially in full in-cell LCDs [1], and (2) to distinguish false touches at which water is dropped onto the touch screen. Recently, there has been an attempt to adopt 2-D self-capacitance multi-touch sensors in flexible OLEDs over 10″ in size to reduce capacitive loads. Due to encapsulation of thickness less than $10\mu \mathrm{m}$ , capacitive loads over 500pF are formed under the conventional bar-type sensor. Nevertheless, there remain problems with limited signal bandwidth, large offset charge, and severe common display noise injection due to a large capacitive load. To overcome the problems, area- and power-efficient AFEs have been announced [2], [3]. However, those studies have only focused on mutual-capacitance sensing with light capacitive load and mostly rely on differential voltages/current signaling, so requiring wider dynamic range and more accurate voltage/current sensing. Therefore, this paper presents a touch screen controller for a 2-D self-capacitance sensor supporting an active stylus in a large capacitive load. The noise antenna reference shielding (NARS) improves immunity to common-mode noise injection, and achieves 27.7dB SNR with in-band common noise of 180pC. Moreover, a baseline current compensator (BCC) provides a large baseline current up to 300pC and extends dynamic range for the external interference. In addition, an area-efficient architecture for the active stylus using single-bin DFT is presented for 216-channel AFEs; it occupies 49.7mm2, and shows 62dB SNR with a 1mm- $\phi$ tip active stylus at 480fps.