What’s the biggest challenge for designs that utilize touch-enabled displays?

Mon, 02/10/2014 - 3:35pm

What’s the biggest challenge for designs that utilize touch-enabled displays?

John Busch, General Manager, Display PVD Group, Applied Materials

Take a look at virtually any new smartphone or tablet device, and whatever the brand or size, they likely have one thing in common — touchscreen displays. This ubiquitous level of adoption comes with challenges, particularly pricing and volume yields to meet mass market needs. The touch-enabled display represents one of the largest cost factors for advanced smartphones and tablets, and as displays move to higher resolutions, OEMs are looking for ways to drive down both the touch element and display to maintain competitive consumer pricing for the end device.

For touch panel production, we are enabling cost-reduction approaches for indium tin oxide (ITO), such as moving to a one-glass solution (OGS) for larger size panels and increasing the adoption of ITO on roll-to-roll film substrates. The industry is also exploring the integration of new film materials and technologies to improve or replace traditional ITO materials, which represents some exciting new opportunities down the road.

From the manufacturing perspective, precision materials engineering is key to providing reliable, ultra-high resolution displays in the volumes demanded by the mobile device industry. Applied Materials has developed equipment solutions that help flat panel display makers implement more advanced transistor technology that also improves device stability, mura* and yield. As the industry moves toward alternative display form factors – curved, flexible, etc., more technology innovations are in store as the choice of substrate and production capabilities will play an even greater role in bringing cost-effective, future generations of advanced high-resolution displays to market.

*Mura: an anomaly in the picture quality visible to the eye

Andrew Blum, Director of Visual Solutions, Rorke Global Solutions, a business unit of Avnet

As a result of the success of advanced smartphones and tablet computing, users have discovered the benefits of projected capacitive (PCAP) touch panel technology. PCAP touch panels are now available in larger panel sizes, enabling designers to bring this same experience to embedded systems where the durability, reliability and overall performance of this technology can add substantial value to their systems but there are design considerations and integration challenges to overcome unlike with any other touch technology.

Application awareness

PCAP touch sensor performance can be compromised with the use of certain gloves or with the presence of certain liquids. Full knowledge of end user interfacing expectations is a must.  For example, high salinity liquids are conductive. Users might experience false touches and/or inconsistent touch performance with the presence of such liquid on the touch sensor surface.  In applications where a user might wear heavy gloves, they may experience an inability to register a touch point consistently because the thickness and material of certain gloves prohibit the transmission of the touch sensing field to the user’s finger.   

Integration awareness

As PCAP technology projects an electric, touch sensing field, this presents a host of challenges for designers.  Touch sensing accuracy and consistency can be greatly affected by EMI noise from surrounding electronics and the proximity of surrounding metal objects like the system chassis. The location of other system components in relation to the touch sensors controller and flat flex connecting tail should be carefully considered in advance of final design.  Additionally, overall use of metals and integration practices should be heavily scrutinized for their effect on PCAP touch performance.   


Fortunately, makers of PCAP components specifically for industrial applications have improved tolerances for these issues. Advanced knowledge of the application and a knowledgeable technology partner can lead to solutions for each of these examples.  Good design choices and a partner like Avnet who works with our customers to review their system designs, offer engineering and integration guidance and can pre-tune out interference issues in the touch controllers firmware set enable fast and trouble free implementation of PCAP technology.


Shahna Kothapally, Vice President of Engineering, Ocular

Projected capacitive (PCAP) touch panels have many advantages, such as extreme durability, enhanced optical clarity and resistance to scratches. Applications such as medical, Point of Sale (POS) and industrial controls benefit from these robust displays. However, since PCAP uses an electrical field to sense a touch, it also presents design challenges based on the environment and the end application requirements. If the end application is in a noisy environment, design choices such as proper grounding schemes, shielded FPCs, strategic locations for the touch controller circuitry and reducing coupling of the TFT noise to the touch panel, will need to be made so that the external noise does not affect the touch panel performance.  Design choices have to be made to increase the Signal-to-Noise ratio of the touch panel to lessen the noise impacts. The end application will also dictate the required display size and scaling to larger sizes can impact the desired performance based on controller specifications. A larger touch panel design will require use of a touch controller with a higher node count to provide optimum performance. The maximum sensor size that can be supported is dependent upon the available touch controllers and node offerings. Trying to use a controller designed for a smaller PCAP will negatively impact the touch accuracy, as well as the pinch separation, of the panel.


Andrew Hsu, Technology Strategist, Synaptics

Designing devices for capacitive touchscreens can be a surprisingly challenging experience for novice designers. Unlike mechanical switches and buttons, a capacitive touchscreen is quite a complicated and sensitive electronic subsystem. Much care and consideration is needed to ensure that the capacitive touchscreen behaves in a reliable and predictable fashion.

The primary hardware design concern for ensuring optimal performance is the elimination of noise from the system, with the most obvious source for a touchscreen coming from the display itself. Starting with a display that emits less noise (such as ones with DC VCom or OLEDs) can significantly improve touchscreen performance.  Another common issue is high frequency noise introduced by noisy power supplies, and one needs to verify that the touchscreen system can withstand this.

Another major design challenge that is typically overlooked is the touchscreen user experience. Even if a device has optimal touch performance (measured directly at the output of the touch controller), the overall touch user experience may still be poor due to apparent latency between the user's touch and the device's response. If the touch hardware appears to be functioning properly – with timely data being reported – a careful examination of the host processing of touch events will be needed to determine the source(s) of latency in the touch-acknowledgement loop.

Beyond overall touch-acknowledgement latency, the other major user experience challenge is the appropriate design of the user interface. Fortunately, widespread smartphone adoption has bred designer familiarity and more touch-oriented UI toolkits are now available. Nevertheless, novice designers need to carefully consider the overall user experience for their device and ensure that the touchscreen interface is intuitive to use and encompasses all the available device control requirements.

Less than a decade after its release, touchscreen development has evolved greatly and become much more reliable and robust for designers. However, it still pays to plan ahead and think through the overall system design to ensure that the device benefits maximally from a capacitive touchscreen.




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