Bus encoding: Difference between revisions

Revision as of 12:45, 9 April 2015

Revision as of 13:02, 9 April 2015

Line 3:

In the context of this article, a system can refer to anything where data is transferred from one element to another over bus (viz. [[System_on_a_chip|System on a Chip]] (SoC), a computer system, an [[embedded system]] on board, etc.).

== Motivation ==

Power consumption in electronic systems is a matter of concern in today's world for the below reasons:

#'''Battery-operated devices''': Due to ubiquity of battery operated devices and the need to maximize the duration between two subsequent charging of the battery, it is necessary that the system consumes as less power (and energy) as possible.

#'''Environmental constraints''': In an attempt to protect the environment, we need to conserve the usable energy. Since the energy consumed by electronic systems is increasing drastically, minimizing the energy consumption of electronic systems is critical to save the environment.

#'''Power Dissipation''': As per the [[Moore's_law|Moore's law]], semiconductor devices have been packing more and more transistors in smaller amount of area. This leads to higher power dissipation per unit area and makes packaging and thermal cooling system design complex and costly. Hence, low power electronic systems are needed to tackle this issue.

The dynamic power dissipated by a CMOS circuit is directly proportional to the activity factor and the load capacitance as seen by the output of the CMOS logic gate. In case of a bus, the load capacitance is usually high since bus needs to be connected to multiple modules and routed longer and the activity factor is also high. Due to higher value of load capacitance and activity factor, in a typical system, bus power consumption can contribute up to 50% of the total power consumption. Bus encoding aims to reduce this power by reducing the amount of activity (number of toggles) in the bus lines. While the kind of bus encoding to be used for a particular system can be best determined when the target application and environmental constraints about the system are known apriori, described below are some techniques which can help reduce bus power for most systems.