For four decades the evolution of integrated circuits has followed Moore’s
law, according to which the number of transistors per square millimeter of
silicon doubles every 18 months. At the same time transistors have become
faster, making possible ever-increasing clock rates in digital circuits. This
trend seems set to continue for at least another decade without slowing down.
Thus, in the near future the processing power of digital circuits will continue
to increase at an accelerating pace.
For analog circuits the evolution of technology is not as beneficial. Thus,
there is a trend to move signal processing functions from the analog domain to
the digital one, which, besides allowing for a higher level of accuracy, provides
savings in power consumption and silicon area, increases robustness, speeds
up the design process, brings flexibility and programmability, and increases
the possibilities for design reuse. In many applications the input and output
signals of the system are inherently analog, preventing all-digital realizations;
at the very least a conversion between analog and digital is needed at the interfaces.
Typically, moving the analog-digital boundary closer to the outside
world increases the bit rate across it.
In telecommunications systems the trend to boost bit rates is based on employing
wider bandwidths and a higher signal-to-noise ratio. At the same time
radio architectures in many applications are evolving toward software-defined
radio, one of the main characteristics of which is the shifting of the analogdigital boundary closer to the antenna.
Because of these trends, there is an urgent need for data converters with
increasing conversion rates and resolution. A part of this needed performance
upgrade comes with the technology evolution, but often the demand is higher
than this alone can provide. Thus, there is still room, and a need, for innovations in circuit design.