IBM announced an improved version of a key component used widely in cell phones and other wireless products. Called a "power amplifier," the tiny circuit is expected to have a big impact in reducing the cost and size of these personal electronic products.

These are the first available radio-frequency (RF) power amplifier products to be fabricated using IBM's advanced Silicon Germanium (SiGe) technology, heralding a new era in the design of portable wireless communications devices.

"This is a breakthrough in this product category," said Dr. Bernard Meyerson, vice president, Communications Resources and Development Center, IBM Microelectronics. "Some experts thought such chips couldn't be done in SiGe, or that they had to be manufactured in gallium-arsenide (GaAs) devices, a process that's expensive."

These SiGe chips "run cooler" than GaAs, taking advantage of the superior thermal conductivity of SiGe, resulting in a measurable improvement in thermal reliability. And since SiGe BiCMOS technology can incorporate numerous important functions on a single chip, the power amps can be manufactured in very small packages, reducing the total layout area on a product's "mother board."

IBM's new power amps will enhance the development of portable wireless communication devices with several competitive features important to wireless OEMs, such as gain, added power efficiency and standby current, while also exceeding the industry requirements for ruggedness.

There are three SiGe power amplifier devices in the suite introduced today. The IBM 2022 TDMA (Time Division Multiple Access) IS-54 power amplifier at 800 MHz; the IBM 2018 CDMA (Code Division Multiple Access) IS-95 also at 800 MHz and the IBM 2017 PCS CDMA IS-95 at 1900 MHz, all manufactured by IBM in its SiGe-based BiCMOS 5AM 0.5 micron technology, offering a combination of enhanced passive device performance, low cost and fast wafer-build time to provide optimum design flexibility. These new chips will be manufactured at IBM's facility in Burlington, VT.

The IBM 2022 TDMA power amplifier is currently available, the IBM 2017 PCS CDMA is available as a prototype and the IBM 2018 CDMA will be available as a prototype next month.

International Business Machines Corporation, New Orchard Road, Armonk, NY 10504. Tel: 914-499-1900. IBM wireless products, visit: www.ibm.com/chips/products/wireless

This silicon-germanium-based (SiGe) power amplifier is a new product family for IBM, making them one of a select few using this technology. Typically, companies making power amplifiers for mobile products use gallium arsenide (GaAs). IBM's introduction comes at a fortuitous time when many designers are rethinking their use of GaAs. Big Blue recognizes that SiGe will be used in the future and that there will be a move by other manufacturers to develop SiGe devices. One reason for the change is that many designers are looking for ways to integrate as many functions as they can, and they can't if they use GaAs. That's not to say that GaAs doesn't perform well, it does. Its performance is the reason most PAs on the market are made from GaAs.

Unfortunately, you can't leverage the benefits of silicon when you use GaAs. For example, most power amplifiers in today's cell phone designs use GaAs, making it one of the few components that has no other integrated functions. In fact, not even the DC bias circuitry is integrated. On the other hand, SiGe is a BiCMOS process that allows high levels of mixed signal integration. Using SiGe technology lets you have on-chip bias control and predictions are that soon you can expect to see other functions integrated into the PA, including the switch, coupler and other discrete functions. Finally, IBM can fabricate SiGe chips on 200 mm wafers, and soon will move to 300 mm wafers, for even better economies of scale.

Another reason for the change is that SiGe is a better conductor than GaAs, so there aren't any hot spots in the middle of the device. IBM says they are confident that the SiGe power amps will have superior thermal reliability to GaAs. Additionally, because SiGe runs cooler it means you don't need any thermal devices such as a heat sink or a metal plug. But the important point about the SiGe running cooler is that it has better reliability and the power amp will last longer.

So why wasn't SiGe used before now for power amps? The reason is mainly because it wasn't able to meet the industry ruggedness specification. For example - if you used a handset and you caught the antenna in your hand - you would get very loud reflections back into the power amplifier. Instead, you would then get very high voltage standing wave ratio (VSWR) and that would effectively cause the PA to blow up. And here's what I think is the coup de grace - IBM added some circuit protection to prevent high VSWR from occurring. Now, the SiGe-based power amps can meet the required standards.

For now, IBM is offering a CDMA version power amp and that will be followed shortly with TDMA and PCS versions.