Mixed Signals

Materials make signal difference
System-on-chip (SoC) design has traditionally catered to an obsession with fine-geometry CMOS. Each process node-the shift from 0.18 to 0.13 microns and then to 90 nanometers-has meant that more functionality could be incorporated on chip. The smaller line widths allow CMOS transistors to function on lower voltages and to trigger on faster clocks. Such an obsession, however, wreaks havoc with analog and mixed-signal designs. With each process shrink, the signal-to-noise ratio declines, and linearity and dynamic range are lost. If analog and mixed analog-digital circuitry represents the means of launching signals into the real world, clearly something more is needed.