M. G. A. Mohamed

Efficient Multi-Touch Detection Algorithm for Large Touch Screen Panels

Large mutual capacitance touch screen panels (TSP) are susceptible to display and ambient noise. This paper presents a multi-touch detection algorithm using an efficient noise compensation technique for large mutual capacitance TSPs. The sources of noise are presented and analyzed. The algorithm includes the steps to overcome each source of noise. The algorithm begins with a calibration technique to overcome the TSP mutual capacitance variation. The algorithm also overcomes the shadow effect of a hand close to TSP and mutual capacitance variation by dynamic threshold calculations. Time and space filters are also used to filter out ambient noise. The experimental results were used to determine the system parameters to achieve the best performance.

Efficient algorithm for accurate touch detection of large touch screen panels

Large mutual capacitance touch screen panels (TSP) are susceptible to display and ambient noise. This paper presents a multi-touch detection algorithm using an efficient noise compensation technique for large mutual capacitance TSPs. The algorithm starts with a calibration technique to overcome TSP mutual capacitance variation. It also overcomes the shadow effect of a hand close to TSP and mutual capacitance variation by applying dynamic threshold calculations. Time and space filters are also used to filter out noise. Experimental results are used to determine system parameters for best performance.

Concurrent Driving Method with Fast Scan Rate for Large Mutual Capacitance Touch Screens

A novel touch screen control technique is introduced, which scans each frame in two steps of concurrent multichannel driving and differential sensing. The proposed technique substantially increases the scan rate and reduces the ambient noise effectively. It is also extended to a multichip architecture to support excessively large touch screens with great scan rate improvement. The proposed method has been implemented using 0.18 μm CMOS TowerJazz process and tested with FPGA and AFE board connecting a 23-inch touch screen. Experimental results show a scan rate improvement of up to 23.8 times and an SNR improvement of 24.6 dB over the conventional method.

Voltage shifting double integration circuit for high sensing resolution of large capacitive touch screen panels

We propose a new touch screen sensing circuit based on voltage shifting double integration scheme for large touch screen panels. The proposed circuit increases the sensing resolution by shifting integrated signal, while reducing the detection time by integrating both edges of sense signals. We implemented the proposed technique in FPGA and analog circuit with touch detection software. Experiments show that the proposed circuit improves both the touch performance and frame rate - key requirements for large touch screen controllers.

Design of a Frequency Division Concurrent sine wave generator for an efficient touch screen controller SoC

This paper presents an interleaved sine wave generator using an efficient memory access technique for large touch screen controllers. It concurrently applies sine waves of different frequencies. The proposed circuit improves the speed of touch detection and reduces the chip area compared with conventional analog oscillators. The range of sine wave frequencies and the gap between each of frequencies can be configured by adjusting the address calculation algorithm to fetch samples values stored in memory. Therefore it provides higher flexibility with configurable sine wave frequencies than conventional schemes. It also minimizes the memory size required to regenerate all the sine waves needed. The proposed architecture has been implemented the proposed sine wave generator in a touch screen controller with FPGA and analog front end board.

Distributed architecture of touch screen controller SoC for large touch screen panels

Currently large touch screen panels (TSP) tend to use projected capacitance technology, which allow multi touch and high sensitivity. For large TSPs with a large number of TX (driving) and RX (sensing) lines, however, it is increasingly challenging to achieve high sensitivity, high detection rate, and multi-touch. In this Paper, we propose a distributed architecture of touch screen controller where multiple controller SoCs collaborate in driving and sensing each section of a large TSP. We show that the proposed architecture and SoC design can increase the detection rate without loss of sensitivity performance. It also allows a smaller SoC implementation, while its chip expandability provides the flexibility of supporting a large range of TSP sizes. We implemented the proposed distributed SoC using TSMC CMOS 0.18um with a low power ARM core, AHB-lite bus, memories, and embedded touch algorithm software.

Utilization-Aware Channel Allocation and Routing for Mesh Networks for Battery-Powered Surveillance Cameras

Battery powered video camera sensors are often connected wirelessly to cover a large area. We propose a multi-channel allocation and routing method for wireless mesh networks where each node generates event-driven video sensor data. How the routing and channel allocation is done has large impact on the battery life time of such networks. We realistically analyze the power consumption model based on the utilization of each link. We then present an optimization formula of utilization-aware channel allocation and routing that minimizes the overall power consumption while transferring all the required video data. We developed an efficient heuristic algorithm that accurately approximates the formula. A network simulator has been developed, which show that the proposed method can reduce the overall power consumption.

Differentiator based sensing circuit for efficient noise suppression of projected mutual-capacitance touch screens

This paper presents a new technique to improve noise immunity of the RX sensing circuit of mutual-capacitance large touch screen panel (TSP). A differentiator circuit is incorporated to effectively suppress the high frequency noise. The proposed architecture provides low-pass and high-pass filter functions to reduce the noise and improve SNR. It uses square wave as a driving signal and integrates the output signal after filtering out the noise. The sensing circuit is small enough so that we can duplicate it to achieve target frame scan rate. We implemented the proposed technique using a 65 nm CMOS process and evaluated its operations in response to various touch events. The experimental results shows that the proposed technique improves the SNR of TSP by 9.5 dB compared to the conventional integrator based sensing circuits. We show that the design consumes 2.7 mA per each sensing circuit with supply voltage of 1.2 V.

New FFT design with enhanced scan rate for frequency division concurrent sensing of mutual-capacitance touch screens

As the touch screens become larger and demand higher resolution, various concurrent sensing methods have been developed for higher scanning speed and performance. One of such fast detection methods called the frequency division concurrent sensing (FDCS) employs an FFT to distinguish concurrent driving sine waves of different frequencies. In this paper, we propose a new FFT architecture and design, which can further improve the speed of the FDCS based controller for large mutual capacitance touch screens. The proposed FFT is used to increase the frame scan rate without duplicating sensing circuit. It uses only half the cycle of the driving signals to reconstruct the complete cycle of the signals, and so it can convert the signals to the complete frequency domain data. This paper shows that the proposed FFT architecture can double the frame scan rate with negligible loss in signal to noise ratio (SNR) and small area overhead.

OFDM and TDM based sensing method for large projected mutual-capacitance touch screens

This paper presents a new technique for reading out projected mutual capacitance touch screen panels. It models touch screen panel as a communication system. Orthogonal frequency division multiplexing (OFDM) is used along with time division multiplexing (TDM) to read out all channels of touch screen panels. Different carrier frequencies are applied to touch screen panel concurrently using OFDM, while the sensing lines are sensed sequentially using TDM. The proposed technique ensures a high frame scan rate by using simultaneous driving signals, and it provides high signal to noise ratio (SNR) by avoiding frequency band with high noise power. Simulation results demonstrate a SNR improvement of 8.2 dB by selecting adequate carrier frequencies.