Basestation boom continues, despite handset slump
By Stephan Ohr, EE Times
May 29, 2001 (2:07 AM)
URL: eetimes.com
Despite the precipitous decline in cellular handset production, the cellular infrastructure is still being built, and the IEEE Microwave Technology and Techniques Symposium (MTT-S) last week was a showcase for its construction
The Phoenix meeting attracted an estimated 8,000 people, who braved 109° temperatures even as they defied corporate travel restrictions to fill downtown hotels close to the Phoenix Civic Plaza.
The consensus among exhibitors was that investments in infrastructure remain in place and that basestation construction continues - albeit at a somewhat slower pace and with some new technical caveats. There also was the suggestion that new infrastructure will rely less on third-generation (3G) implementations, building more on 2.5G and data enhancements to existing modulation schemes, such as General Packet Radio Services and EDGE.
Partly this is due to an industry-wide recognition that implementing full Internet browsers and a 2Mbit/second wireless network represents a major technology leap. "Broadband networking is not trivial," said Cliff Vaughn, business development manager for Motorola Semiconductor Products Sector (Phoenix). "People who believed it was easy to put an entire Internet browser in your handset were obviously smoking some good stuff. Even NTT fell on its face."
Cell phone makers may have overestimated the dimensions and requirements of the high-end market, agreed Norman Brodeur, marketing manager with M/A-Com (Lowell, Mass). The true consumers of novelty handsets would be teenagers, for whom the phones would have to be ultracheap with, say, leopardskin faceplates, he suggested. Japanese teens, for example, do not consume high-data-rate services, opting for horoscopes and crude text messages, he said.
The slowdown in handset manufacturing has been drastic, Brodeur observed. The industry went from euphoria to depression in just a few short months, "as if a switch flipped." The slowdown, he said, was due to excess cell phone inventory - manufacturers simply built too many - and it will take a long time to use up the backlog.
But the slowdown in handset production hasn't affected infrastructure construction in the same way. M/A-Com is seeing such building in 2.5G areas and new design wins in the 3G space, Brodeur said. Like other manufacturers at MTT-S, M/A-Com exhibited 3G basestation components - the exuberance on the show floor suggested there would be willing customers for those parts.
For example, manufacturers of LDMOS transistors, typically used as the antenna drivers in cellular basestations, are reporting little slowdown. In fact, a short-term glitch in Ericsson Components' manufacturing process - which left the passivation layer of its LDMOS transistors vulnerable to temperature cycling - forced other manufacturers to fill the slack in an up-to-now-buoyant market, altering market shares at the end of 2000.
'Robust' sector
So UltraRF (Sunnyvale, Calif) perked up its catalogue offerings with second-sources of Motorola and Ericsson LDMOS parts. While much of its current consumption can be characterised as prototype productions (1,000 devices per week) in the service of one or two major customers, marketing vice president John Quinn insists he has seen no slowdown. Much of the new business is in the 2.1GHz 3G arena, a sector he called "robust."
The two major problems facing LDMOS manufacturers are getting the costs down (dollars per watt) and increasing power density (watts per square inch). The current target is 300 W/inch2. "We're not quite there yet," said Quinn, "but that's what the world wants."
For LDMOS maker Xemod, (Santa Clara, Calif) business has been so active that the company had to set up a new assembly facility in Tempe, Arizona, said marketing vice president Richard Clark. Xemod designs its own LDMOS parts but relies on foundries to make them. At MTT-S, Xemod demonstrated LDMOS-based power amplifier modules capable of delivering up to 350W for wideband-CDMA applications. The modules have a 47dB gain and are intended to simplify new-generation basestation design with a drop-in part.
"Much of the 3G stuff has been pushed out," Clark acknowledged. "It was too big a technology leap." But this left basestation manufacturers with a greater concern for the costs and efficiencies of their designs. Clark also believes the stretch-out of 3G introductions has created more support for EDGE. Instead of 2Mbits/s, basestation makers are seeing what they can do at 384kbits/s.
In addition to low-power, 3-W LDMOS transistor arrays, Motorola was touting its new carbon-based silicon germanium process (SiGe:C). Motorola announced manufacturing qualification for the process in February. At MTT-S, the company announced the first product utilising the process - a low-noise amplifier (LNA) with a built-in bypass switch. The switch allows large signals to bypass the LNA to prevent overload, said RF applications engineer Kelvin Leung. The switch device features low insertion loss (2.5dB) and a low noise figure (less than 1.38dB at 1.9GHz).
The device offers 14.5dB of gain, but consumes 9mA of current. SiGe:C is effectively a bipolar process that consumes more power than CMOS. However, the LNA is biased to be highly linear, said Motorola applications-engineering manager Mark Williams - and any highly biased device will consume more current than an unbiased switch.
Rather, the SiGe:C process will enable bipolar driver transistors to be implanted on a CMOS substrate. The resulting BiCMOS will enable much higher levels of integration for basestation transceiver components, said Williams. Motorola is hoping SiGe:C will replace GaAs front-end components in 2.1, 2.4 and 5.7GHz applications, he said.
Other basestation offerings
Support for new-generation basestations was visible in the products shown at MTT-S by M/A-Com. Defence accounts for only 25% of the $900m annual revenue at the former military and aerospace supplier, whose GaAs and wireless-component business is now largely commercial, said marketing manager Brodeur. Much of the product line supports the wireless handset infrastructure.
It introduced at the conference a co-siting diplexer and control ICs for W-CDMA basestation transmitters. A diplexer is a wavelength resonant chamber that segregates transmit and receive frequencies at the basestation antenna. The co-siting diplexer enables multiple transmission schemes as the same basestation site. These can be UMTS and GSM900 (for European installations) or AMPS and PCS1900 (in the US). "It's driven by regional preferences," said Will Landry, senior engineering manager for amplifier products. The diplexer he was marketing had a 0.4dB insertion loss.
For new-generation CDMA and GSM basestations, M/A-Com engineering manager Phil Beucler promoted feed-forward amplifier components consisting of a digitally controlled delay line, a variable-gain amplifier and a vector modulator. The delay line controls crosstalk in multifrequency amplifier chains and controls signal propagation to 50ps steps. The device will support UMTS (frequencies up to 2.2GHz) and has a 750ps dynamic range.
The vector modulator controls amplitude and phase independently - up to 360° of phase control. Meanwhile, the gain control amplifier has 25dB of gain and 10dB of attenuation, controllable in 0.25dB steps. |
