Conferences and supporting programme
A Novel PCap Sensing Technology for Electronic Touch Displays
Today's touch controller solutions based on analogue and mixed-signal components can be difficult to manage during the product development phases of design, integration, tuning, and manufacturing. Adding pen support into devices from phones to large interactive flat panels is also challenging. Design constraints of Projected Capacitive (PCAP) based touch systems require system engineers to essentially design around the sensitivities of the analogue or mixed signal based touch panel. From component positioning, to ground planes, from optical stack-ups to placement of individual traces the impact to the touch panel performance must be considered in nearly every design decision. The difficulty in working with sensitive analogue components in PCAP based systems is their propensity for false signals generated by noise emanating from the LCD, the ground plane, the environment, and even from parasitic capacitance between electrodes. The latter problem regarding parasitics is especially limiting in large screen PCAP based systems. Current analogue components are not discerning but are sensitive to noise throughout the system. Digital systems incorporate powerful signal processing techniques that provide robust noise elimination resulting in high SNR. We use Sigma-delta methods with advanced digital signal processing to overcome the problems of traditional PCAP touch sensors. Our architecture offers multi-mode concurrent touch sensor sampling of Self, Mutual and Pen, with true simultaneous sampling of all channels. A low-cost programmable digital architecture provides fast spectral processing and advanced filtering methods for excellent noise rejection with high SNR. Sigma-delta modulators are well known and are used for high-resolution ADC and DAC applications. They perform noise shaping, filtering, decimation, and are inexpensive to produce. One of the unique characteristics Sigma-delta converters is that the frequency transfer functions for the input signal and quantization noise are different thereby enabling signal creation with a very high SNR. Our flexible signalling method allows for multiple frequencies and simultaneous drive/sampling independently on each row and column of a touch sensor. This provides concurrent modality which means both self and mutual capacitance detection is performed in the same sample cycle. Further, different frequencies can be used for simultaneous object recognition. We use a Sigma-delta drive on each channel that allows for the channel frequencies to be adapted in real-time to avoid environmental noise. This, along with powerful digital filtering that rejects out-of-band noise, and a very high SNR signal, means that our approach has exceptional noise immunity that meaningfully reduces the painful tuning process common in today’s analogue PCAP systems while at the same time improving touch sensitivity and system reliability. We propose a new approach for touch, hover and object detection using Capacitive Imaging that provides greater advantages than the high sensitivity analogue ICs and does not share their weaknesses. The ability to differentiate signals and predict behaviour can have a profound impact on system design. This approach is highly flexible and will operate with in-cell, on-cell and discrete sensor implementations. Migration to programmable digital silicon with channels driven by flexible I/O provide important architectural options and cost advantages.
--- Date: 27.02.2019 Time: 1:35 PM - 1:55 PM Location: Conference Counter NCC Ost