(A) compact and noise-immune capacitive touch-screen controller based on 2D coded-aperture read-out

Abstract

As mutual-capacitive touch-screens expand their application area to various information devices, better controllers are in demand for larger, thinner, lower-cost touch-screen panels (TSP), and in-cell/on-cell touch displays. In order to gain higher sensitivity from such large and noisy TSPs, numerous parallel analog circuits are integrated on TSP controllers. Many solutions to cope with harsh noise environments require sophisticated signal conditioning circuits to be duplicated on every channel, easily consuming higher analog power and increasing silicon cost.

This dissertation presents an ultra-compact, low-power and noise-immune mutual-capacitance TSP controller based on a 2D coded-aperture read-out architecture, which obtains a TSP’s response to a set of 2D basis patterns, based on the widely known notion that all kinds of 2D images can be transformed into other orthogonal basis domains, e.g., frequency or pseudo-random noise. Sensing whole TSP channels projected into a single-channel circuit prevents hardware redundancy due to a requirement for parallel circuits and enables designers to focus on maximizing noise-filtering performance with less concern about hardware cost. Even with a single-channel circuit, this method facilitates all mutual capacitor-nodes to be driven simultaneously, therefore fully retaining high noise-immunity advantages of the previously reported CDMS method.

The dissertation also covers high-level characterization of 1D-/2D-CDMS sensor read-out system. Important design issues, such as coding considerations, reconstruction algorithms, spectral signal characteristics, and coded-shutter problem, for implementing CDMS read-out system is discussed.

This work also introduces a simple and effective implementation of continuous-time synchronous demodulation RX circuit for capacitive sensor read-outs featuring the wave-shaping mixer. By adopting harmonic-rejection mixing concept and efficiently embedding it into $2^{nd}$-order switched-capacitor sigma-delta modulator, the RX circuit easily performs harmonic-rejection function for enhanced noise-immunity for TSP controller with the simplest circuit architecture.

The prototype IC for the architecture was fabricated in a 0.18-$\mu$m CMOS technology using 1.8/3.3 V transistors. By adopting 2D coded-aperture-based read-out for 24 TX × 16 RX touch-screen panel, the controller obtained 53 or 38 dB SNR for untouched and touched tests, respectively. Thanks to single-channel implementation advantages, the circuit occupies only 0.46$mm^2$ active silicon area and consumes 2.6 mW under 1.8/3.3 V supplies.

This dissertation also presents a novel 3×VDD TX driver for TSP controller using a standard CMOS technology. To handle high-voltage up to three-times of the nominal $V_{DD}$ without gate-oxide breakdown or hot-carrier degradation, the driver circuit utilizes newly introduced fractal-chain inverter circuit to keep any of transistor voltage differences being stressed no more than the nominal $V_{DD}$, regardless of variant loading conditions. The prototype chip on 0.18-$\mu$m 1.8/3.3 V deep-n-well technology successfully outputs ~9.9 V swing during six-days long burn-out test, implying long-term reliability of the circuit.