TABLE OF CONTENTS Power dissipation has become a top priority for today's microprocessors. Previously a concern mainly for mobile devices, it has now become extremely important for general-purpose and even high-performance microprocessors, especially with the recent industry emphasis on processor "Performance-per-Watt."
The power dissipated by typical modern circuits can be broken up into three main categories: dynamic or switching power, short circuit power, and leakage power. Dynamic power is due to the charging and discharging parasitic capacitance of transistors during logic transitions. This power is typically expressed in a simplified form:
where ? is the average transition probability, C tot is the total load capacitance being switched, V dd is the supply voltage, and f is the operating frequency.
Short circuit power is induced when NMOS and PMOS transistors are conducting simultaneously, causing a short current flowing through from the power supply to the ground. It can be expressed as a function of rise and fall times:
where t r and t f are the rise and fall times of the input, respectively. I p is the saturation current of the circuit, and it is directly proportional to the size of the transistors. The primary item to note about this source of power is that, as technology scales and clock speeds increase, the typical waveform gets further and further away from the ideal square wave. As a result, the time spent in transition between logic high and logic low (i.e., the rise and fall times...
