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3.3.3 Frequency Scaling

Equation 3.1 predicts that when the supply voltage is held constant and the frequency is scaled by a factor of $s_{f}$, the dynamic power consumption scales by $s_{f}$ too.

In reality, most commercial systems do not undergo pure constant field scaling. To obtain higher performance than promised by constant field scaling, slightly higher supply voltages and correspondingly higher frequencies are used. This situation can be modeled as voltage/frequency scaling layered on top of constant field scaling. When the supply voltage is scaled by a factor of $s_{v}$ and the operating frequency is scaled by $s_{f}$ the dynamic power consumption scales by $s_{v}^{2}s_{f}$.

In the interest of obtaining satisfactory noise margin, circuits are typically designed to operate at voltages that are several times higher than the threshold voltage of transistors. Since the threshold voltage does not scale as rapidly as transistor feature size, supply voltage cannot be reduced considerably in the future if noise margins are to be maintained. Combined with the issue of increasing leakage current, these factors indicate that technology scaling alone may not be adequate to alleviate the power consumption problems of future systems.



Binu Mathew