11.6 A 100-TRX-channel configurable 85-to-385Hz-frame-rate analog front-end for touch controller with highly enhanced noise immunity of 20Vpp

Touch screens have recently been adopted not only for smartphones but also for tablet PCs and home appliances that have touch-screen panels (TSPs) larger than 10 inches. However, there are many sources of noise that affect touch detection, and some of these noise sources, such as charger noise, significantly affect the capacitance variation needed to detect touch input and lead to inaccurate touch detection [1–2]. For example, as shown in Fig. 11.6.1, common-mode supply noise results in large peak-to-peak noise injection over 10Vpp and deteriorates touch-detection performance. Although rejection of display noise using the differential sensing method [3] has been investigated, sufficient attenuation of the injected noise through a touch object remains a problem. In this paper, we present an analog front-end (AFE) with noise immunity of up to 20Vpp for a large TSP controller. To improve the immunity to the injected noise, the proposed AFE employs the following techniques: a) TX/RX dual modulation, b) differential sensing, c) high-order noise filtering, and d) multiple TX driving frequency support. Further, to cope with various usages and advanced touch-detection modes, the proposed AFE provides a configurable frame rate from 85 to 385Hz.