ABSTRACT
Since an electrical voltage/current level (which is proportional to the number of electrons) is the only physical property that can be sensed by any electronic device, the flow-of-time inside electrical world must be quantified through this medium. This is achieved by employing an electrical pulse train called a clock signal. The moments in the flow-of-time are determined from this clock pulse train’s voltage level transitions: The moment of its voltage crosses a predefined threshold in the low-to-high (or high-to-low) transition. Therefore, any noise associated with the voltage level around the threshold area will be converted into timing noise [1,2]. This mechanism is illustrated in Figure 13.1. As shown, the voltage level uncertainty ΔV is reflected as timing uncertainty Δt when viewing from a timing perspective. For this reason, all circuits designed for generating a clock signal (i.e., the clock generator or
CONTENTS
13.1 Clock Generator Must Be Mixed-Signal Circuit .................................... 325 13.2 Phase-Locked Loop: Today’s Mainstream Clock Generator
and Its Limitation ....................................................................................... 328 13.3 Future Electronic System Demands More from Its Clocking ............. 329 13.4 A Flexible Clock Generator: Time-Average-Frequency Direct
Period Synthesis ......................................................................................... 331 13.5 IC Clocking Is More Than PLL Design ...................................................334 13.6 TAF-DPS: A Circuit Level Enabler for System Level Innovation ........335 13.7 Conclusion: The Philosophical Debate of Spectrally Pure
Clock versus Flexible Clock ......................................................................344 References .............................................................................................................346
