Microwatt Power CMOS Analog Circuit Designs: Ultralow Power LSIs for Power-Aware Applications
One promising area of research in microelectronics is the development of ultralow power LSIs. These LSIs would be suitable for use in power-aware LSI applications such as portable mobile devices, RFID tags, implantable medical devices, and smart sensor devices. These LSIs have to operate with ultralow power, that is, a few microwatts or less, because they will probably be placed under conditions where they rely on poor energy sources such as microbatteries or energy-scavenging devices . For example, to operate for more than a year with a nominal coin-type lithium batteries (160 mAh), the power dissipations of these LSIs have to be less than 60 μW, and for more than 3 years, they have to be less than 20 μW.
To achieve such low-power dissipations, we can use simple low-power techniques utilizing ultralow currents and low-supply voltages biasing. In analog circuits, we can reduce the power dissipation by using ultralow current biases of 0.1–100 nA, and in digital circuits, by a lower supply voltages than threshold voltages of MOSFETs because the power dissipations are proportional to the bias currents and the square of the supply voltage. This means that, using the ultralow current and ultralow voltage biases, the circuits are operated in the subthreshold region ...