Neonode: zForce

Recently, Neonode's optical touch solution - zForce hits ASUS portable device. The most possible is tablet such 5~13" display size. That's very interesting. Compared with iPad that use 9.7" (in diagonal) capacitive touch panel, ASUS pad-like product could use bigger size. Bigger size, higher cost for capacitive touch. Maybe it is the cost issue make zForce attractive.

In 2008, Neonode had pushed its cellphone N2 with their optical touch module, designed user interface and special gesture operation functions. Neonode's strategy focused on mobile/portable device market is very different with other optical touch companies that almost play in sizer over 15" because small size is dominant by capacitive or resistive touch.


Structure
Neonode's optical touch is conventional infrared light array which span as a grid pattern, so determinate the position of pointer (finger, pen....any infrared obstructive object) by the blocked signal. From the picture below, the two IR LED line arrays are arranged along two side of display and the photodetectors arrays are on the opposite side. For power concerned, it can active portion of LED and photodetectors depending on the user interface on display - it only sensing area where buttons located.

Embodiment in Mobile phone
Neonode claims optical touch advantages:

• No overlay -100% transmission display
• Cost effective
• Low power consumption

cross-section

From cross-section view, the LED and photodetectors are located beside of liquid crystal display and there are reflective elements like mirror guide infrared light passed above the surface. Without any film overlaid  on display does not absorb any light emitted from TFT-LCD.
Challenges

• Ambient light
  Portable device must encounter outdoor environment that many infrared sources may cause error motion. For long developed time of conventional optical touch technique, ambient light suppression can be done by modulation frequency, designed activation and subtraction algorithm, optical filter and special bezel design.
• Resolution
  For higher resolution, it is need more dense LED and PD arrangement but at cost of price. According to a review paper, Neonode N2 has 2.5 beams/cm and so finger has 9 beams blocked signal. (On contrast, iphone has 7 traces/cm and so 25 traces for finger touch. Capacitive has higher resolution advantage) But the newer product zForce may have higher resolution spec.
• Bezel height
  This is the basic physical limitation because it need reflective elements to pass IR light above surface. You can see the ugly protrusion of LCD display in the photo of Neonode N2.
• Ambiguity
  From the picture above, the two types of 2 fingers touch mode have the same blocked signal and make the ambiguity problem in determining position. Neonode not only uses blocked signal but also reflected signal to solve the ghost fingers, and more it can distinguish by adding corner LEDs to get more blocked signal information.
• Multi-touch
  Two points are almost the limit of optical touch. Neonode three fingers demo is really amazing but the special operation like piano can't tell their truly 3 points ability.
• Power consumption
  LED is driven by current and wast more power if many LEDs light on simultaneously so they must put much effort in activation control.
• Cost
  LED and PD are not low if there are numbers.

More

In Neonode's patents, there is a very interesting structure "embedded reflective element". The structure is a infrared transparent layer with embedded reflective elements and LED and PD are on the side, so infrared light can guided to display surface like the visible light of LCD. The position is determined by the reflected light from finger, guided by embedded reflective elements and detected by PD. It can make the height of module thiner but lost its original advantage "no overlay and 100% transmission".