Patent Background

When a touch sensitive device is poorly grounded, recognizing a touch event could become difficult. The poor grounding could cause touch values representing the touch event to be erroneous or otherwise distorted by undesirable capacitive coupling introduced into the device. Consequently, actions to be performed based on the touch event could likewise be erroneous or otherwise distorted.

Patent Summary

Apple's invention relates to ground detection for a touch sensitive device like an iPad. A future iPad could detect its grounded state so that poor grounding could be compensated for in touch signals outputted by the iPad. The iPad may include one or more components that monitor certain conditions. The iPad will be able to analyze the monitored conditions to determine whether it's grounded.

A future iPad may selectively apply a function to compensate its touch signal outputs if the iPad determines that it is poorly grounded. Conversely, the iPad could selectively ignore the function if it determines that it's well grounded. Ground detection could advantageously provide improved touch sensing and power savings by not having to repeat measurements subject to poor device grounding. Additionally, the iPad could more robustly adapt to various grounding conditions.

The iPad to Gain Connector Sensors

Apple's patent FIG. 1 illustrates an iPad having a connector sensor that could be used for detecting a grounded state of the device according to various embodiments. As you could see, a future iPad may have two USB connectors as shown as #2 on the right side and # 3 at the bottom. This would support other Apple filings. The iPad may also gain a Power Cable port on the left side noted as #1. A future iPad dock would correspondingly support the new ports.

In Patent FIG. 1, The Connector Sensor 13a could sense power from the power cable 12 via the connector port 10a. The sensed power could indicate that the iPad is plugged into a wall outlet, for example, thereby grounding the device through the wall ground. Therefore, sensing power via the connector port 10a could indicate that the iPad is grounded such that negative pixel compensation could be either deactivated or reduced, if currently active, or can remain inactive otherwise, when the touch panel 11 produces touch signals. The same is true for connector port 10b, whereby the connector sensor senses that a USB cable has been plugged in and so forth.

Negative Pixel Compensation

When a well grounded touch sensitive device receives a touch by an object, such as a user's fingers, the device's mutual signal capacitance (Csig) at the touch location could be properly changed to produce a pixel touch output value indicative of a true touch event. However, when a poorly grounded touch sensitive device receives a touch by an object, such as a user's fingers, undesirable charge coupling called negative capacitance (Cneg) could be introduced into the device to cause the pixel touch output value to be in the opposite direction of the intended mutual capacitance change. As such, a pixel experiencing touch under poor grounding conditions could appear to detect less of a touch than is actually present, known as a "negative pixel."

Negative pixel compensation could be selectively applied to the negative pixel touch output value to reduce or eliminate the negative pixel effect. However, to be effective, the negative pixel compensation should be applied under appropriate conditions and in appropriate amounts. Since negative capacitance (Cneg) could be a function of how well the touch sensitive device is grounded, the device's grounded state could be detected so that negative pixel compensation could be applied as needed. The detection could be done by monitoring various touch sensitive device parameters indicative of the device's grounding and determining the grounding based on the monitored parameters' values.

Apple's patent FIGS. 1 through 5 illustrate exemplary device parameters and corresponding device components that determine the parameters' values which could be used for detecting a grounded state of a touch sensitive device according to various embodiments.

Apple's patent FIGS. 2,3 and 4 points to various sensors that the iPad will use that could be used for detecting its grounded state. They include motion, proximity and perimeter sensors. The perimeter sensor will be implemented in the iPad's frontside bezel, though the patent states that the sensors could be placed on the back as well. The users touch grounds the iPad.

Apple's patent FIG. 7 illustrates an exemplary method for detecting a grounded state of a touch sensitive device like an iPad.

Future iPad Notification System

In Apple's patent FIG. 5, we see an illustration of a future iPad having a notification algorithm that could be used to detect its grounded state. If the grounding is poor, the iPad will communicate such to the user via a new notification system.

Vibrations Unique to Humans

Sensing the orientation and motion of the iPad could give an indication of the iPad's current status, which could be indicative of the device's grounded state. For example, if the iPad's motion sensor 22 (noted in FIG. 2 above), senses a particular pattern, frequency, and/or magnitude of vibrations unique to humans, the device could determine that it is in contact with a user, e.g., being held, and therefore grounded. These patterns, frequencies, and/or magnitudes could be predetermined or could be "learned" if the user places the iPad into a learning state while holding, moving, or walking around with it.

If the motion sensor senses motion that is determined not to be human vibrations, the iPad could use additional information about the object moving the device to determine whether the device is grounded. Conversely, if the motion sensor senses that the iPad is substantially stationary and/or oriented in a particular manner, the iPad could determine that it is in a dock or on a surface. If in a dock, the iPad could use additional information, e.g., the dock connections, to determine whether the device is grounded. If on a surface, the iPad could use additional information, e.g., the device connections or the surface, to determine whether the device is grounded. The iPad could selectively apply negative pixel compensation to the touch signals based on the determination.

Sensing a surface proximate to the iPad could identify the type of surface, e.g., wood, metal, plastic, organic, inorganic, human, and so on. For example, sensing a proximate human surface could be an indication that the iPad is being held by a user or resting in the user's lap and therefore grounded. As such, negative pixel compensation can be deactivated or reduced, if currently active, or could otherwise remain inactive.

Sensing a proximate wood surface could be an indication that the iPad is resting on a table top and therefore likely poorly grounded. As such, negative pixel compensation could be adjusted, if currently active, or activated, if currently inactive, to apply to touch signals from the touch panel. Sensing a rubber surface could be an indication that the iPad is in a protective case and therefore likely poorly grounded, even if held by the user since the rubber can act as an insulator.

Apple credits Steve Hotelling, David Amm, Michael Lammers, John Orchard, Brian King, Omar Leung and Deniz Teoman as the inventors of this January 2011 patent application, originally filed in Q3 2009. For the sake of trivia, the original filing listed the ARM 968 processor as a candidate for the iPad.

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