Introduction to VLSI Design Flow

Power-driven optimization is an integral part of a design flow. Various design steps, such as systemlevel design, logic synthesis, and physical design, consider reducing power dissipation as one of their objectives. We carry out power-driven optimization and include power reduction techniques throughout the flow. Nevertheless, for easy readability, we present a consolidated view of these techniques in this chapter.

MOTIVATION

We need to reduce the power dissipated by an integrated circuit (IC) due to the following reasons:

• 1. The energy that a circuit draws from the power source gets stored internally or gets dissipated to the environment through packaging and heat sinks [1]. We can relax the cooling requirement of an IC by reducing its power dissipation. Thus, it allows us to use simpler and less costly packaging and heat sinks.

• 2. An IC draws power from a battery, especially in portable devices such as mobiles and laptops. For a given battery, we can reduce the frequency of recharges by reducing its energy consumption. To an approximation, we can view a fully charged battery as delivering a fixed amount of energy. Therefore, we need to reduce the average power or total energy dissipated by the circuit to reduce the frequency of recharges [2]. Alternatively, we can reduce the battery weight by reducing the average power dissipation for a given recharging frequency. From the environmental perspective too, consuming less power is desirable.

• 3. The power dissipated in an IC gets manifested as an increase in its temperature. When the temperature of an IC increases, some device failure mechanisms exacerbate. By reducing power dissipation in an IC, we can avoid significant temperature increases and the associated reliability issues.

When we reduce the power dissipation in an IC, we often sacrifice other figures of merit, such as performance and area. Therefore, as a designer, power reduction is never our sole objective. We intelligently trade-off other metrics such as performance while achieving power reduction.