New chip promises longer battery life

Researchers of the University of Rochester have developed a wireless chip for cellphones that needs ten times less power than current designs. The new chip relies on a technology named injection locked frequency divider (ILFD) and permits to dramatically reduce the time needed to check for transmission frequencies.

It always happens when you need it the most: the battery of you cellphone just died. But now, researchers of the University of Rochester have developed a wireless chip that needs ten times less power than current designs. The new chip relies on a technology named injection locked frequency divider (ILFD) and permits to dramatically reduce the time needed to check for transmission frequencies which are performed several billion times per second by your current phone. The new chip uses five transistors and can perform divisions by 3 instead of only 2 by previous circuits, allowing a perfect communication between two phones communicating at 2.0001 and 2.0002 gigahertz respectively.

Here is the introduction of the University of Rochester news release.

Hui Wu, professor of electrical and computer engineering at the University of Rochester, a pioneer in a circuit design called an "injection locked frequency divider," or ILFD, has solved the last hurdle to making the new method work. Wireless chip manufacturers have been aware of ILFD and its ability to ensure accurate data transfer using much less energy than traditional digital methods, but the technique had two fatal flaws: it could not handle a wide range of frequencies, and could not ensure a fine enough resolution within that range.

Now these two problems have been solved. Below is a picture of the system used to develop Hui Wu's new chip (Credit: University of Rochester).

Hui Wu's new chip

But what's so new in this chip? First, you need to know that your phone must maintain a very accurate and stable clock at all times, and that a special circuit called "phase-locked loop" is usually activated several billion times per second, eating your battery juice.

This is where Wu's new design makes the practical application of ILFDs possible. He introduced a new topology into this circuitry--instead of the old three-transistor design, his has five transistors--creating what he calls "differential mixing." The new circuitry topology allows the ILFD to divide by three as well as two.

Below is a micrograph of the chip (Credit: University of Rochester).

A micrograph of Hui Wu's new chip

And why this division by three affects your battery life?

This tiny change has huge ramifications. A circuit design that can divide by two or three can, for instance, divide 9,999 clock pulses by two, and the 10,000th by 3, giving an average of 2.0001, which could be the frequency at which the cell phone is trying to communicate. Should the phone need to communicate at 2.0002 gigahertz, the ILFD could divide 9,998 clock pulses by two, and the 9,999th and 10,000th by three, yielding an average of 2.0002. By varying how many clock pulses are divided by two or by three, any frequency can be selected, making the power-saving ILFD method viable for the first time.

This research work has been presented at the 2006 IEEE International Solid-State Circuit Conference (ISSCC) under the name "A 16-to-18GHz 0.18μm Epi-CMOS Divide-by-3 Injection-Locked Frequency Divider." And here is a link to this techical paper (PDF format, 3 pages, 289 KB) from which the above picture of the micrograph has been extracted.

Now the researchers are working on the next generation of wireless communication devices which will probably use the 60 GHz band for which this new chip will be even more efficient. This is good news for people on the road.

Sources: University of Rochester news release, via EurekAlert!, April 19, 2006; and various web sites

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