Bus encoding: Difference between revisions

Revision as of 11:40, 1 April 2015

Revision as of 11:45, 1 April 2015

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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|embedded system]] on board, etc.).

== Background ==

Power consumed by any system can be classified into 2 major categories:

# Dynamic power: Dynamic power is the power which is consumed when there is any activity in the system (any element changes its state). Dynamic power is also referred as active power.

# Static power: Static power is the power consumed in the system even if the system is idle and doing no activity. Static power is also referred as [[Leakage_(electronics)|Leakage power]].

== Motivation ==

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 gate. In case of a bus, the load capacitance is usually higher 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 upto 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.