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.