3. Power Saving Techniques

As the transistor gets smaller, the distance from the source and drain side terminals becomes narrower. There is a resulting increase in the probability that electrons will be able to jump the gap even when they are in the off position, a phenomenon called leakage. A technique to combat this leakage is to apply a bias voltage to the transistor, which effectively increases the transistor's threshold voltage. This technique of applying extra voltage is called back bias; the greater the voltage, the less likely is leakage across the channel. ATI boasts that back bias can increase battery life by 10-15%.

Techniques like dynamic clock scaling and clock gating decrease power consumption when there is low workload. The first technique automatically and dynamically controls the clock frequencies of the core - and components in the core - according to the load on the graphics subsystem. The latter is used to switch off function blocks that are not being used, and switching them on again later as needed.

Two other advances in power management come in the form of dynamic voltage control, and using transistor combinations that use differing voltages. Dynamic voltage control is a part of ATI's "Power-On-Demand" feature, and allows the voltages to be scaled dynamically as the workload on the GPU dictates. ATI says that the "Mobility Radeon X1600 GPU is designed to provide stable operation when supplied with as little as 0.95 volts, which allows it to dramatically reduce power consumption in power saving modes." By using transistors with differing threshold voltages combined in the same design, the chip can continue to run at lower clock speeds with modified data paths, and thus consume less power.

A final power saving technique is to turn off the PCI Express bus lanes when they are not needed. Called Dynamic Lane Count Switching, this effectively puts the card at 1x when it is not rendering 3D applications or when in a dormant state (blank screen) to prolong battery life. This feature, coupled with back bias, low-k dielectrics, clock gating, dynamic clock scaling and voltage control, can add valuable life to the entire system when on the go.