In addition, the response speed varies depending on the position of a finger. In the proximity state, it is about 50ms and about 10ms in the contact state. In respect to power consumption, "there is no difference between the two states," the spokesperson said.
To improve the sensitivity in the proximity state, multiple sensors are connected to increase the sensor area. In general, sensitivity improves in proportion to sensor area.
Furthermore, a function called "sensor shield control" was added to reduce the parasitic capacity of the circuit. The electrodes in the x-axis direction and those in the y-axis direction are located ones on top of the others. When sensors are operating, the sensitivity lowers due to the increase of parasitic capacity caused by the electric potential difference between the upper and lower parts of the electrodes.
Therefore, Mitsubishi Electric reduced the parasitic capacity by applying signals of the same phase and potential. Also, the sensor shield control function eliminated the need for a shield layer that reduces electromagnetic noise generated from an LCD panel.
Only few changes made
The prototype is based on a capacitive touch panel that is available on the market, and "only a few changes were made to it," according to the spokesperson. Mitsubishi Electric just added switch elements to connect multiple sensors and improved the detection circuit to reduce its parasitic capacity, he said.
"Our research and development division does not consider that those improvements will significantly increase costs," he said.
The commercialization schedule of the new touch panel has not been determined yet. But when it is commercialized, "it will first be used for our products," the spokesperson said. The company plans to verify its resistance to environment as well as operability in actual devices for the commercialization.
The capacitive method employed for the prototype is a projection type, which is suitable for mobile devices and difficult to be applied to large screens. But Mitsubishi Electric is now working on measures to meet the requirements of screens that are 10 inches or larger. The new detection method cannot be realized with surface capacitive touch panels, according to the company.