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Projected-Capacitive Touch Sensing Technology

Projected-capacitive (PCAP) touch sensing technology is rapidly evolving to meet the advanced user-interface needs of modern applications. Popular consumer products that use multitouch and gestures have fueled an increased demand for projected-capacitive touch solutions beyond these applications. People expect to interact with most devices in the same manner as their smart phones and tablets. The challenge is that not all applications can afford the hardware, software and power budget associated with the current smartphone-optimized designs.

Applications such as security control panels, keypads, thermostats, gaming devices, remote controls and wearables have very different requirements with regard to response time, number of touches, power consumption and cost. The ability to optimize the touch controller and sensor solution to meet these requirements is crucial for the industry to expand beyond the main consumer applications.

One of the primary challenges of expanding projected-capacitive sensing technology into other markets is power consumption. The relatively high power consumption of most touch applications has limited their adoption in low-power input devices. Most embedded devices have user expectations for battery life measured in months and years, not hours like our current mobile devices. Power-consumption requirements and management become critical during the evaluation of projected-capacitive technology. The optimal combination of PCAP code with extreme low power management has enabled customers to address these power constraints while adding the PCAP touch and gesture functionality.

As an example, single-touch tap, swipe, swipe and hold, and double-tap gestures can be deployed using lowpower and inexpensive electronics solutions. Performance data for a small 1” X 2” sensor running at 2V can have low power usage of ~15 uA in an active idle mode, waiting for a touch, and only 150 uA for active scanning. In a recent design win, this translated into a 2+ year battery life. Remote controls, gaming controls and other power-conscious devices can benefit from these advancements in PCAP technology and power management. As with all applications, there are sometimes performance tradeoffs, but power, size and other characteristics can be managed to meet the low-power design requirements.

Flexibility is the next challenge to expanding projected-capacitive touch sensing into new markets. The rapidly emerging market trend of incorporating touch and gestures into a wide range of devices outside the traditional mobile market requires customers to also move quickly to keep up with competition. The resulting fast design cycles require progressive and flexible PCAP touch controllers and sensor design options.

Traditional PCAP solutions have long design cycles with rigid implementations, consisting of an ASIC-style touch controller and fixed sensor design. Many suppliers of touch technology offer dedicated black-box, ASIC-style touch controllers that match up with specific touch sensors. They work for their dedicated application, but the customer has limited design flexibility. These fixed solutions do not allow for code modifications, if a small change is introduced during the development or production cycle. For example, if a designer wants to make a simple sensor design change in size or construction, this type of change could be considered a redesign and would require extensive work with the touch-sensor supplier to update their code and sensor design.

Also, these closed solutions do not allow customers to integrate code for other functions, such as LED control, WiFi, or IR into the same controller to create a multi-functional device with touch. Customers can miss opportunities for cost reduction and efficiency by being locked into a closed solution. It is also difficult for customers to manage their development cycles and to deploy next-generation designs for cost reduction and feature enhancement.

Customers should not be boxed in by hardware and software in their PCAP solution. One approach to meet the challenge of providing flexible design changes and efficiencies is to empower designers with source-code access and tools that enable them to independently make further customization and create optimized solutions for their applications. This design flexibility allows customers to manage their touch-interface solutions to enable fast and targeted modifications on their own timetables without depending on external vendors.

The sensor is the third challenge in enabling other markets to adopt projected- capacitive touch sensing. Touch sensors in the mobile market are often proprietary designs with limited access to supply chains. This restricted access presents a sourcing challenge as well as functional uncertainty for those that try to make their own custom solution. Fortunately, the recent development of various types of inexpensive projected-capacitive touch sensors that are easily available and manufacturable now enable designers to start working on these new market segments with PCAPenabled designs.

Some examples of these sensor types include touch pads and flexible sensors. Typical touchpads are inexpensive sensors based on a printed circuit board (PCB) that can be used under a plastic overlay material, similar to the look and feel of the touchpad on laptops. These standard sensor designs provide the desired smooth-surface feel, with tap and swipe touch response, to everyday interfaces on applications such as gaming devices, light switches, automotive consoles and remote controls.

Other sensors options include flexible printed circuit (FPC) sensors and printed sensors with conductive inks. These flexible sensors offer options for designs with curved surfaces or backlit keypads that need cutouts for LED lighting. Advancements in transparent printed conductors are quickly developing to provide inexpensive and manufacturable transparent touch sensors for lower-cost display solutions, including wearable applications.

Touch solutions are rapidly evolving and proliferating into many designs, beyond the smartphone or tablet markets. Customers are seeking ways to add touch interfaces and gestures into their designs that are both easy to integrate and address the typical design challenges discussed here. Limited power budgets and the need for flexible design options for touch-controller and sensor solutions are no longer obstacles for projected-capacitive sensing technology to be used in everyday embedded applications.

This article was written by By Carol Crawford, Director, Touch-Screen Controllers, and Charlie Riegert, Product Manager, Touch-Screen Controllers, Microchip Technology Inc. (Chandler, AZ). For more information, contact Ms. Crawford at Carol. This email address is being protected from spambots. You need JavaScript enabled to view it., Mr. Riegert at This email address is being protected from spambots. You need JavaScript enabled to view it. or visit http://info.hotims.com/45609-201.