Will 3.3 Volt Systems Solve the Power Crunch?

In the early sixties, automobile manufacturers switched from 6 volt to 12 volt battery systems to accommodate the greater power demands of modern cars. In the computer business, the reverse trend is in effect. Designers want to reduce the voltage and thereby reduce power consumption and extend battery life. Current microcomputers, including pen computers, are based on 5 volt systems. In other words, the voltage supplied to the CPU, memory, and peripheral devices is 5 volts. The new trend is towards 3.3 volt systems.

First Come Hybrids

The first phase of this trend is to employ so-called “hybrid” or “flexible” 3.3 volt processors, which can operate with either 3.3 or 5 volt devices. In this phase, the CPU and memory operate at 3.3 volts, while components such as the keyboard, disk drive, and display controllers still operate at 5 volts. In the next few years, entire systems will be designed to operate at 3.3 volts. For example, the ARM and Hobbit processors to be used in Apple’s Newton and in the AT&T/GO device respectively (see cover story) will operate at 3.3 volts. Intel recently announced a “flexible voltage” version of its 80386SL processor. Memory, video controller, disk drive, and display manufacturers are also working on 3.3 volt versions of their products.

The relationship between power consumption and voltage is not linear and varies depending on whether direct or alternating current is used so there is no exact figure for the amount of power that will be saved in 3.3 volt systems. In the case of direct current, the power is proportional to the square of the voltage, resulting in a 56% reduction in power consumption in the CPU, core logic, memory, and video control of 3.3 volt systems versus equivalent 5 volt systems. Other components show smaller reductions in power. In general, system vendors are talking about an overall 30 to 40% reduction in power consumption for complete 3.3 volt systems. However, there are mitigating factors. Backlit displays consume just as much power in 3.3 volt systems as in 5 volt. Also, clock speeds cannot be set as high on 3.3 volt CPUs, thus reducing the potential performance of 3.3 volt parts.

Full 3.3V Systems Two Years Off

In spite of the promise of 3.3 volt systems, it will take a couple of years before full 3.3 volt systems are available. Vendors of peripherals have to develop 3.3 volt manufacturing capability and there are various design issues to be resolved. But 3.3 volt systems will eventually offer major benefits to mobile, compact computer systems. The lower voltage will generate less heat, allowing for more compact packaging. And battery life should increase from 30 to 40% in 3.3 volt computers. Coupled with advances in battery storage technology, 3.3 volt systems could be the turning point in producing systems with truly acceptable battery life.