  Factors that contribute to the rapid increase in power dissipation as a
function of input bandwidth in high speed electronic Analog-to-Digital
Converters (ADCs) are discussed. We find that the figure of merit (FOM),
defined as the energy required per conversion step, increases linearly with
bandwidth for high-speed ADCs with moderate to high resolution, or
equivalently, the power dissipation increases quadratically. It is shown that
by use of photonic time-stretch technique, it is possible to have ADCs in which
this FOM remains constant for up to 10 GHz input RF frequency. Using this
technique, it is also possible to overcome the barrier to achieving high
resolution caused by clock jitter and speed limitations of electronics in such
ADCs.
  Use of optics is actively being pursued for reducing power dissipation and
achieving higher data-rates for board-level and chip-level serial communication
links. In the same manner, we expect that optics will also help in reducing
power dissipation in high-speed ADCs in addition to providing broader
bandwidths.
