Area-Efficient Readout IC with High Panel Noise Rejection for Capacitive Touchscreens
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Abstract
As capacitive sensing provides flexible and reliable touch user interfaces for a varied set of applications, it has gained popularity over other touch sensing techniques. Consequently, capacitive touchscreens when interfaced with large display panels increases the number of channels that a readout IC has to support. As existing area-intensive touchscreen controllers are upgraded to support increased channel counts, the additional silicon area requirement increases the product cost. In addition, the touchscreen performance is highly affected by LCD noise and external noise from battery chargers. This thesis describes the design and implementation of a new area-efficient touchscreen readout architecture. The proposed mixed-signal architecture is a compact solution implemented in a 0.15 ?m CMOS process with a per channel area of 40 k?m2. The readout architecture has a bandpass channel response to filter the strong panel noise sources more effectively. An SNR of 18 dB with panel noise in a measurement bandwidth of 200 Hz was obtained for a 4.3? capacitive touchscreen panel with a channel pitch of 4.1 mm.