Design Feature: August 18, 1994

Don't believe that square pegs are always destined for round holes, or that you'll always arrive in the right place at the wrong time. Also, forget depressing stories about military decline leaving contractors nowhere to go. Often things do work out well, "win-win" situations really exist, and former military suppliers can find their talents in even greater demand today.

Such is the experience of the staff at UK-based GEC Plessey Semiconductors, who, with a long service record as prime military communications contractor to the UK's Ministry of Defense (MOD), has seen a new era of demand for commercial wireless products rapidly eclipse traditional communications business.

Wireless technology permeates an increasingly wider range of today's commercial products. Currently, the company's ICs and modules find application in a range of personal-communications products, wireless LANs (WLANs), global-positioning-by-satellite equipment, and intelligent vehicle-highway systems.

An element of good fortune has played some part in bringing about GEC Plessey's business transformation. For, well before it became evident wireless products would be a major growth market, the company already possessed the necessary range of technologies. Essentially, GEC Plessey specializes in microwave and RF, with an in-house armory of 0.7-mm CMOS, RF bipolar, silicon-on-sapphire (SOS), SAW (surface-acoustic-wave) filters, crystal oscillators, thin-film hybrids, and multichip modules (MCMs). Significantly, the company has more than a decade of experience in applying spread-spectrum techniques (Ref 1), in addition to extensive volume manufacturing and testing expertise.

But of all the technologies, the company regards its high-speed bipolar process, known internally as "HE," as the linchpin of its entire wireless strategy. Significantly, development grants from the UK's MOD provided some of the funding for this advanced process.

HE is a double polysilicon trench-isolated process that produces high-frequency performance, has low power consumption, and enables high circuit density. The process produces transistors with an effective emitter width of 0.4 µm and a peak fT of 15 GHz at 2.5 mA I_C. The process uses three layers of metallization and achieves high density by allowing contacts over vias.

A significant feature of the process is an ability to include on-chip resistors, capacitors, and inductors. Overall RF performance also relies on polysilicon resistors and the trench isolation structure to minimize parasitic components.

To develop on-chip capacitors, the process introduces a silicon nitride dielectric between two of the metal layers. The high value of the capacitors (0.65 nF/mm²) enables circuit tuning as well as RF decoupling.

For on-chip inductors, the process uses the top metallization layer. This layer is made approximately twice as thick as the lower layers to reduce resistance and thereby increase the inductors' Q.

Minimizing the number of external components for an RF IC is the hallmark of many GEC Plessey designs. The HE process even provides varactor diodes to enable on-chip tuning of voltage-controlled oscillators. Placing complete RF subsystems on-chip makes the ICs easier and faster to design-in. RF handling of final products becomes more stable and predictable, is less susceptible to external effects, and is less likely to emit spurious signals.

The company's major applications for the HE technology include prescalers for PLLs up to 6 GHz, low-power (15-mW) prescalers, direct waveform synthesizers to 2 GHz, 100-MHz ADCs, 500-MHz DACs, and integrated radio front ends for cellular, cordless, and global-positioning products.

Picture 1

While GEC Plessey holds its bipolar process in high esteem, the company admits that some of its recent RF ICs have now forced the HE process to its performance limits. Also, market drivers, particularly lower prices for automotive electronics and decreasing physical size in the personal-communications sector, constantly apply further pressure to upgrade. In anticipation, the company's next-generation bipolar process--designated "HG"--is set to debut in the next 12 months and will broadly double the speed/power ratio of the process. In parallel with this development, GEC Plessey will follow a path of higher integration through expanded use of MCMs, although the company notes that, currently, MCMs are too expensive for some sections of the market.

Of course, technology alone wasn't responsible for the company's smooth transition from military to commercial wireless business. (In fact, GEC Plessey still serves a wide range of military users.) Gaining success and recognition in a commercial market, however, called for some internal company changes, especially affecting design staff.

Brian Hyde, worldwide marketing manager for GEC Plessey's communication group, identifies time-to-market as the single driving force in bringing about these changes. First, Hyde says the days of projects lasting several years are over. What's more, simply meeting shorter time scales does not guarantee success. In today's business, you need a race mentality because you're always contesting your progress against a competitor's. Also, you need to clearly differentiate your product from others: "me-too" products lead nowhere.

Hyde identifies design tools and staff attitude as two factors that are instrumental in bringing about a race mentality. To reduce design times, GEC Plessey has made substantial investments in EDA tools. And, to improve productivity, a flatter and less formal management structure has brought designers closer to users--and engendered commercial awareness. As further impetus, GEC Plessey designers prefer working with products that support concord in place of conflict. The work is more motivating and satisfying, which, in turn, further raises productivity.

With RF capability to over 2 GHz, GEC Plessey already has major emerging digital-wireless standard frequencies covered (Ref 2). Currently, though, the company reports that worldwide analog-cellular business outstrips digital cellular by approximately 10 times, and, despite market hype, that situation will prevail in the short term. The company makes the point that in underdeveloped countries with poor line communications, installing a basic analog cellular system costs less than extending land lines. Digital systems, although offering fancy facilities, work out to be too expensive in these areas. Accordingly, the company plans further integration of its existing analog cellular chip sets.

WLANs create major potential

According to GEC Plessey, WLANs represent the company's largest market-growth potential. WLANs are a natural market for GEC Plessey, mainly because of the frequency-hopping spread-spectrum technology requirement. In fact, WLANs became the first commercial application for spread-spectrum techniques, simply because the networks were assigned an unlicensed operating band (2.4 to 2.483 MHz) already occupied by microwave ovens and home and auto radar alarms. Entering the band as a secondary user meant that designs must not interfere with, or be susceptible to, existing signals in the band.

Picture 2

GEC Plessey has progressively refined its DE6003 600-kbps WLAN module over the two years since its introduction. Integration has now reached a physical limit consistent with its low cost of $250 (10,000). The latest iteration suits a PCMCIA format but also allows board space for a user's protocol gate array. The company plans an additional 50% size reduction in an MCM version, although currently cost prohibits its introduction.

Longer-term work on WLANs entails moving to the 5.15- to 5.3-GHz band and increasing data rates to a 20-Mbps payload. This project, known as HiperLAN, involves GEC Plessey in partnership with Apple Computer Europe and Advanced RISC Machines (ARM). The consortium will build a demonstration system with financial backing from the European Commission. The European Technical Standards Institute (ETSI) is currently developing the HiperLAN standard. The applications that HiperLAN will open up carry enormous market potential, ranging from office-LAN PC file sharing, email, and printing to video telephony, TV distribution, and real-time remote data acquisition and processing.

GEC Plessey's experience with global positioning indicates a general requirement for a high level of support. These users, for example, in automotive or navigational products sectors, are generally inexperienced in RF-design work. The company has responded by offering RF modules to ease users into the business. More recently, it introduced a Global Positioning by Satellite Builder (GPS-Builder), which is a 12-channel development system on a PC plug-in card ($3950). The product includes the pc-board-layout and software source code to assist users in developing their own systems.

As for the future, in general, GEC Plessey will concentrate on higher levels of integration and lower power consumption in its wireless products, while staying abreast of emerging international standards. The company is quietly keeping watch on future possibilities for commercial satellite communications, knowing full well its in-house SOS capability is ready and waiting. In short, the company simply intends to do more of what it already does well: designing advanced RF products. And, being in the right place at the right time also helps; Europe is the place to be for initiating wireless standards and implementing systems.

1. Gallant, John, "Digital wireless networks," EDN, March 4, 1993, pg 78.

2. Gallant, John, "ICs and modules for digital wireless communications," EDN, August 19, 1993, pg 77.