It is much easier for engineers to solve the thermal management issue if the device has low heat dissipation to start with. The core of the problem is the processor, because it can easily make up 20 to 50 per cent of total heat dissipation. It is concentrated on a few square centimetres of circuit board, which usually also contains other high-performance components like the system memory. This is one reason why thermal aspects are taken into account during the circuit board design process. The device’s casing needs to conduct heat away and is often in direct thermal contact with the processor. All these points contribute to making the end system more expensive.
So what is the best way to optimise the processor’s power consumption? To answer this, we need to look at each of the different causes of power dissipation separately. Every transistor switch generates electrical losses by switching the smallest charges, which are characterised by dynamic power consumption. The level of these losses depends on the clock frequency being used. A lower clock frequency will generate correspondingly low losses. Although each new semiconductor generation has reduced the power consumption per transistor, the number of transistors used has increased, as has the clock speed.
While structure widths up to about 90nm only cause dynamic losses, deep sub-micron architectures also feature static losses – in other words, leakage current. This arises due to unavoidable tunnel effects, regardless of whether the transistor is switching or not. Leakage current is extremely