Modern ultra-low-power microcontrollers have reached such a level of integration and processing efficiency that many applications no longer require traditional batteries. These applications include complex and often power-intensive wireless sensor networks that may involve sampling various sensors and communicating wirelessly.
By harvesting miniscule amounts of wasted energy from the environment, such systems are enabled with near infinite up-time without a battery as its primary power source. Not only does energy harvesting enhance current applications by eliminating their dependency on the battery, but it also enables entirely new applications that weren't feasible given the finite lifetime and size of batteries.
Ultra–low-power embedded processing
Similar to Moore's Law, which defines the trend of digital technology to double in transistor count every two years, an inverse trend occurs for power consumption. Roughly every 18 months, the power dissipation of digital systems is cut in half.
Advancements in power efficiency already had dramatic results for small, ultra-low-power microcontrollers (MCUs) specifically designed for battery-powered applications and have resulted in designs where battery life has exceeded 10 years. For typical ultra-low-power MCUs, it's common for standby current to be in the < 1 µA range and active current consumption in the ~200 µA/MIPS range. Since the clock rate of these MCUs is typically in the order of 25 MHz or less, the peak current consumption is always relatively small and can be powered with simple power supplies.
Power consumption of a given application is rarely characterized by a single MCU's current draw. Analog conversion circuitry, power regulation, and communication devices each play a part in the system and consume power even when they're not active. By integrating the functionality of each of the devices into a single device using a single low-power fabrication process, it's not only possible to significantly reduce the leakage current of the overall system, but by giving a single MCU control to disable peripherals that are not in use, power consumption can be reduced even further. A single, highly integrated device will typically consume less power than separate discrete solutions; a single device also simplifies the design and reduces the cost and area required for a given function.
Flexible power requirements for ultra-low-power microcontrollers not only reduce power consumption by allowing lower supply voltages than typical embedded processors with a fixed supply voltage, they also allow a wider variety of energy sources. For example, some ultra-low power MCUs support a wide input voltage range between 1.8 V to 3.6 V.1 By allowing a lower operating voltage, this type of MCU can reduce the overall power consumption of the system and use power at the much lower voltage levels provided by the energy harvester.
