Industry’s First Optical Lid Sensor Chip for Tablet Computers and Notebooks

The company is also announcing that the chip uses a new patent-pending optical approach for sensing the presence of a lid or fabric cover on touch-screen products. This approach replaces the standard method of using magnets or mechanical switches. The optical method is less expensive, more reliable and makes it much easier to power down a tablet computer by using a fabric or leather cover without the need to align an embedded magnet over a pickup sensor.

Capella's patent-pending approach is the first optical solution that allows a touch screen to distinguish the shadow of a closed lid (or fabric cover) from the shadow of a user's hand. This distinction allows the touch screen to power down when a lid is closed, but to stay powered as a hand holds the screen and hovers to make selections. The new chip has the sensitivity and intelligence to recognize a hand from the ability of human skin to transmit an infrared light beam whereas a lid or fabric cover is opaque.

Patent-Pending Optical Lid Sensing Technology

The CM36262 chip works in conjunction with an adjacent infrared LED that shines a beam straight out of a touch-screen glass. When the chip's proximity sensor photodiode detects darkness, it can distinguish that a hand is over the screen because the infrared beam will propagate throughout the skin giving it a glow that is detected by the chip's lid sensor photodiode. When the chip's proximity light sensor detects darkness without the infrared glow, it concludes that the lid is closed and it sends a signal over its I2C serial interface for the touch screen to be put into power down mode.

According to Cheng-chung Shih, President and CEO of Capella Microsystems, Inc, “This new integrated circuit is the culmination of many years of research and development by our dedicated engineering team working together in both the United States and Taiwan. The timing of our announcement is perfect because touch-screen manufacturers are pushing the state-of-the-art in their next generation of devices and our optical sensing technology will allow them to push the envelope even further.

The CM36262 chip use's Capella's patented Dual Filtron technology and a wide range of circuits to accomplish its sensing functions. The lid-sensor photodiode feeds an 8-bit A/D converter which passes its digital output to a digital signal processor (DSP) running proprietary algorithms. The high-accuracy ambient-light sensor connects to a 16-bit A/D converter and transfers its digital output to the same DSP. The chip includes infrared diode drivers in either current mode or open collector mode, and a serial I2C bus to communicate with the microprocessor in a touch-screen computer, notebook or smartphone. The chip operates in a range of 2.6 to 3.7 volts, and the typical current consumption is 180 microamps.

Ambient Light Sensor

The chip's ambient light sensor uses Capella's patented Filtron™ technology to detect the lighting conditions surrounding a touch screen and automatically adjust the brightness to closely match the response of the human eye. This close match eliminates excessive screen lighting thereby reducing eye strain and extending battery life. In addition to its optical lid sensor and ambient light sensor, the chip contains a digital low-pass filter that removes fluorescent light flicker.

Patent Filtron™ Optical Filter Technology

The chip's patented Filtron™ technology elimi­nates the need for external optical filters for both the proximity and ambient light sensors. The patented Filtron™ technology allows the fabrication of an array of microscopic optical band-pass filters directly on top of the photodiode detectors. The proximity sensor diode in the new chip is topped with a microscopic infrared filter made using the Filtron™ semiconductor process. The same process also covers the ambient light sensor diode with a tiny photometric optical band-pass filter that passes only the green light band (450 to 650 nm) that matches the brightness sensing mechanism of the human eye.

Proximity Sensor

The proximity function in the new chip increases battery life by enabling portable products to automati­cally turn off their screens when there has been no hand activity over the screen for a period. The function also deactivates a touch screen phone so that it does not dial numbers when in contact with a user’s head. The proximity sensor can also be used in backlit keyboards that allow a user to type in dark areas such as airplane cabins. When a user’s hands move away from the keyboard the proximity function allows the back light to be turned off, and when the user’s hands return to the keyboard, the backlight is switched on.