Tag Archives: Smart Phones

What is a dual screen smartphone?

Most of us use smartphones that sport dual features such as two cameras, two flashes and two SIM sockets. Some manufacturers also make phones with two glass layers for encasing the device. However, one manufacturer has literally followed the adage – two heads are better than one – and produced a smartphone with two screens.

The world’s first dual screen phone – YotaPhone 2 – Is a product of the Russian company, YotaPhone. While the primary display measures 5.0 inches and is an AMOLED display of 1080x1920p resolution and a pixel density of 441ppi, there is a second display on the rear panel. This has a dimension of 4.7 inches, a resolution of 960x540p, a pixel density of 235ppi and is an e-ink display.

The e-ink, rear panel display of YotaPhone 2 has a back matte finish that makes it easy to read from the black and white display. Both, the primary front AMOLED display and the secondary rear e-ink display are protected with a highly resilient layer of Corning Gorilla Glass 3.

Since the secondary display is fully touch-sensitive, you can personalize it easily. For example, rig it up to display notifications and it will show all information of your choice. The main advantage of having a secondary display is power savings. Waking up the full-color display just to check on notifications about messages and mails requires a lot of power. Using the secondary display consumes only a fraction of the power required by the main display.

While on the high-resolution front display you can play games and watch movies, the monochrome rear display is more suitable for static functions such as reading e-books. It is easy to operate one screen at a time, since you can lock out the other one. Operating with the monochrome display saves considerable battery power. However, there is one disadvantage with the monochrome display. An imprint of the previous image can still linger on when you have changed to a new one.

The driver behind the YotaPhone 2 is a Qualcomm Snapdragon 800 SoC. This runs on a 2.3GHz quad core Krait 400 CPU and an Adreno 330 GPU. A healthy RAM storage of 2GB is supplemented with a phone memory of 32GB. YotaPhone 2 comes with an 8MP rear camera and a 2MP front-facing camera. Out of the box, the phone runs Android 4.4 and to accommodate the secondary screen functions, YotaPhone provides the necessary firmware tweaks.

A non-removable, 2500mAH battery powers the device. The phone is capable of being wirelessly charged. YotaPhone has, by design, not provided a very large battery as the secondary screen provides power saving benefits. Additionally, the lighter weight of the battery offsets the increase in the weight of the phone because of the presence of two screens. Additional weight would have made the phone inconvenient to carry. As such, the presence of two displays has significantly increased the thickness of the device.

YotaPhone 2 is fitted with a glass fiber body. This is solid enough considering the weight of the phone at 140gms and a thickness of 8.9mm. The soft curvy edges deserve applause.

MCUs: Interesting things happen within smart phones and tablets

Cell phones and tablets have several interesting things within them such as touch-screens, cameras, gesture sensors, USB interfacing, battery charge monitoring, and many others. Most of these individual functions need tiny components called micro-controller units or MCUs. Of course, additional components are also required such as ADC or Analog to Digital Converters, PWM or Pulse Width Modulators, LCDs or Liquid Crystal Displays and capacitive touch screen interfaces.

The role of MCUs in modern cell phones and tablets can be appreciated by the different functions they handle. MCUs communicate with several analog sensors that in turn, take in analog signals and convert these into digital values. For example, high-end products may have temperature sensors such as RTDs, thermistors and humidity sensors. Others may have accelerometers for measuring 2- or 3-axis movement and convert this input into a digital signal for the MCU to handle.

Smartphones use several types of sensors that require handling by MCUs. ALS or Ambient Light Sensors allow automatic control of the display backlight brightness. This happens over a wide range of illumination conditions ranging from a dark room to direct sunlight. Magnetic sensors gauge the magnetic field intensity for indicating the North. Cameras and proximity sensors offer face and hand movement detection. This is useful for the MCU to switch on the keypad when the user’s hand comes near. IR proximity sensors in conjunction with the camera allow the MCU to switch on the touch screen by detecting the closeness of the user’s face, ear or head. Not only does this eliminate false touches on the touch screen, it reduced battery drain by shutting down unnecessary functions.

MCUs in smartphones dynamically regulate the transmission power when a human is near. In tablets, this is dependent on the Specific Absorption Rate or SAR. SAR is the rate at which the human body absorbs electromagnetic energy when exposed to radio frequencies.

Low-cost cell phones use a mechanical keypad, and an MCU decodes the user inputs. Another MCU handles the Lithium-ion battery charging and its optimal charge life. High-end cell phones have a touch screen and an MCU provides the interface. It uses Haptics or tactile feedback technology for detecting touch, force, vibration or motion of the human body parts near the screen.

USB interface is another very useful function provided by an MCU. It connects several external peripherals to the application processor within the smartphone in a host and slave mode for transferring data from the peripherals at high speeds.

Designers and manufacturers are now combining MCUs with programmable logic and high-performance analog-to-digital conversion capabilities. These are called the programmable system on chip or PSoC. They also have memory integrated into them.

By design, PSoC devices consume negligible amounts of power when in standby mode, making them eminently suitable for use in cellphones. Further design and operation complexity is reduced by having internal op-amps, comparators and ADCs within the PSoC. Sample and hold capability allows sensing and monitoring of slowly varying inputs such as from the battery or a temperature-measuring device. With the use of PSoC, manufacturers have been able to minimize PCB size for cell phone applications largely.