Ultra-Low-Voltage IC Design Methods

The emerging nanoscale technologies inherently offer transistors working with low voltage levels and are optimized for low-power operation. However, these technologies lack quality electronic components vital for reliable analog and/or mixed-signal design (e.g., resistor, capacitor, etc.) as they are predominantly used in high-performance digital designs. Moreover, the voltage headroom, ESD properties, the maximum current densities, parasitic effects, process fluctuations, aging effects, and many other parameters are superior in verified-by-time CMOS processes using planar transistors. This is the main reason, why low-voltage, low-power high-performance analog and mixed-signal circuits are still being designed in mature process nodes. In the proposed chapter, we bring an overview of main challenges and design techniques effectively applicable for ultra-low-voltage and low-power analog integrated circuits in nanoscale technologies. New design challenges and limitations linked with a low value of the supply voltage, the process fluctuation, device mismatch, and other effects are discussed. In the later part of the chapter, conventional and unconventional design techniques (bulk-driven approach, floating-gate, dynamic threshold, etc.) to design analog integrated circuits towards ultra-low-voltage systems and applications are described. Examples of ultra-low-voltage analog ICs blocks (an operational amplifier, a voltage comparator, a charge pump, etc.) designed in a standard CMOS technology using the unconventional design approach are presented.