How to use hover in a user interface

Christi Juchmes, Cypress Semiconductor Corp.

December 14, 2011

Christi Juchmes, Cypress Semiconductor Corp.

Currently, some UIs use a long press to open up new command menus. Using a long press decreases the speed at which the user can interface with the phone and creates a slower, more awkward user experience. But adding hover functionality to a capacitive touchscreen device can remove the need for long presses or force measurement altogether. Hover is to touch what touch is to a long press—by enabling this kind of sensing, OS designers can preserve functionality without having to slow down the UX (users’ experience) or modify threshold and sensitivity levels to calculate Z-Force. With hover, a user no longer needs to apply varying force to perform certain functions or sacrifice efficiency when using the system.

How hover works
Real hover sensing is enabled by a combination of self and mutual capacitance sensing. Both types have advantages and disadvantages. Mutual capacitance is what enables multi-touch functionality. Mutual capacitance touchscreens have horizontal and vertical rows of sensors, like self capacitance screens, but capacitance is measured through the intersections of these sensors (X*Y) instead of as individual sensors (X+Y), shown in Figure 3. Best-in-class touchscreen controllers in the mobile space offer 32 sensor channels for sensing a 4.5" (16:9 aspect ratio) touchscreen with an ideal sensor pitch of 5 mm. Because this type of measurement dramatically increases the possible number of sensors on a panel--a potential of 256 intersections, as opposed to 32 sensor lines for self capacitance--mutual capacitance scanning can deliver higher accuracy and true multi-touch capability. Figure 3 shows five fingers on a mutual capacitance touchscreen. All five input points are clearly identified, with no positional ambiguity.

Figure 3: Mutual capacitance sensors can sense multiple input points by measuring the intersection of X and Y sensor lines, instead of the lines themselves. All five fingers are clearly identified on the sensor grid in this GUI screen capture.


However, mutual capacitance devices require lower noise thresholds as well increased sensitivity to support advanced features like hover technology, which makes them susceptible to performance disruptions from conducted noise.

Self capacitance, on the other hand, is a robust method of sensing. It generates a stronger signal and is capable of projecting larger fields than mutual capacitance, which enables the touchscreen controller to accurately pick up the capacitance of objects (like a finger hovering over the screen). Self capacitance can also provide more touch sensitivity without lowering the noise threshold. That makes it far less susceptible to false touches, poor accuracy, and delayed response times than mutual capacitance.

But for all its benefits, the problem with self capacitance is that it does not support true multi-touch functionality because of an issue known as ghosting, where the position of the two fingers on a screen is ambiguous. In self capacitance sensing, input is measured for change along the horizontal and vertical axes (X+Y). This results in positional ambiguity if the user touches two places on the same line. Resolving this problem becomes impossible with a third touch. Figure 4 is an example of this kind of ambiguity in a self capacitance touchscreen. The red circles are actual touches on the X and Y sensor lines. Because each line now reads a touch, the intersection of those lines register touches (marked in blue) as well, even though none are present.


To deliver accurate hover functionality, a touchscreen controller must use both methods. However, this functionality is not always easy to achieve. Some touchscreen controller manufacturers use two different chips—one for self capacitance and one for mutual capacitance, which adds more silicon to a design. This significantly increases materials cost and imposes limitations on device size as designers must make room for another chip on the board. What device manufacturers really need is a touchscreen controller capable of providing both self and mutual capacitance sensing on the same chip, with the ability to switch between both methods while in application. This keeps materials cost and device size down by eliminating the need for a second chip. By using a touchscreen controller that combines self capacitance, mutual capacitance, and the ability to switch dynamically between them, mobile-device manufacturers are able to design hover functionality into the user interface.

Learn hover craft
Hover technology will dramatically change the way we interact with handheld devices. App, mobile, and OS developers are already designing with hover use cases in mind for their upcoming releases. Other emerging technologies, such as 3D mobile displays, create new opportunities and applications for hover sensing. All market indicators point to hover functionality becoming a major industry trend within the next two years, which means that OEMs should start researching this technology. Integrated hover and multi-touch capability can only be enabled by touchscreen controllers that support both self and mutual capacitance sensing. To keep costs low, designers should look for touchscreen controllers with the ability to deliver both on the same chip. By solving long-standing problems like force measurements and operation with gloves, plus adding new features and commands, hover is poised to make a major impact on the mobile device industry.

Christi Juchmes is a product marketing specialist at Cypress Semiconductor Corp. She can be reached at christi.juchmes@cypress.com.

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