New Growth in Wireless Telecom
Ruth DeJule, Associate Editor -- Semiconductor International, 6/1/1999
F or the past 15 years, the wireless communications market has seen a steady, sustained growth of greater than 20% annually. Dominated by the cellular/personal communications service (PCS) phone market, applications include land mobile radio, paging and messaging with new applications of very small aperture terminal (VSAT) and direct broadcast satellite (DBS) links. Third-generation wireless phones, anticipated in the next 12 to 18 months, could boost the market by as much as 50% to a growth of 30% annually, noted Cliff Vaughan, RF marketing manager at Fujitsu Semiconductor (San Jose, Calif.). A significant portion of this growth is expected in >2 GHz applications. This means an increase in demand for analog GaAs semiconductor devices (see Figure); the driver being the need for RF amplifiers with high linearity over a 60 dB range because of modulation and detection requirements of these systems.
Currently, silicon-based BJTs and LDMOS sufficiently meet the requirements for wireless applications below 2 GHz with amplifier linearities over a 10 to 15 dB range. Primarily used for small signal amplifiers, mixers and low-noise amplifiers in wireless handsets and high-power amplifiers in infrastructure equipment, improvement in performance continues. Manufacturers such as Siemens AG and Philips Semiconductors have developed silicon bipolar processes with a benchmark frequency, fT, of 25 GHz and useable operating frequencies of 2.5 to 3.0 GHz. To increase frequency response, the base region must shrink. Philips Semiconductors' fifth-generation RF wide-band transistors are based on a double-polysilicon process. Operating at these higher operating frequencies but at lower supply voltages appears to be an emerging trend in the use of bipolar devices, noted Professor Gregory Stillman of the University of Illinois (Urbana, Ill.).
| GaAs is projected to gain market share because of the growth in cellular/PCS, automotive and emerging high frequency applications. (Source: Dataquest) |
However, there is a growing demand for still higher frequency devices for applications such as space division multiple access (SDMA) links operating at frequencies as high as 20 GHz and collision avoidance devices that operate at 76 GHz (today with two 38 GHz amplifiers). While the development of silicon-based materials such as SiGe is being pursued and operation of &0.3 µm Bi-CMOS devices at 40 GHz has been demonstrated, reliability and power consumption may be an issue for these applications. Today's portable phones have evolved from analog wireless handset communication where only a single user occupied a channel. It has progressed to second-generation multiple user channels (time division multiplex access (TDMA) used in the U.S. and GSM used in Europe) and first-generation code division multiplex access (CDMA) systems. The wide band third-generation phones will add high speed data applications and video to their increased audio capabilities. Originally developed for secured satellite and battlefield communications, these 2.2 to 2.4 GHz W-CDMA-based handsets require ultra-linear amplifiers to eliminate sidebands created with high data rate switching within the channels. GaAs-based devices can provide the power and single-stage amplification requirements of wireless communication applications with improved linearity and power efficiency at frequencies of 2 GHz and above, according to Dave Ahmari, director of technical marketing at EpiWorks (Urbana, Ill.). At comparable frequencies and input powers to silicon devices, GaAs can provide up to 20% additional gain.
While several device technologies are being investigated, heterojunction bipolar transistor (HBT) devices using InGaP/GaAs and AlGaAs/GaAs are drawing interest. HBTs use different materials for the emitter and base, which define the heterojunction. For example, in an InGaP/GaAs HBT, the wider bandgap InGaP emitter permits higher current gain, thus providing greater flexibility in minimizing the base resistance and emitter capacitance needed to achieve high frequency performance. The potential of GaAs-based HBT technology is high-performance, high-efficiency devices with fT >100 GHz, noted Ahmari.
Philips to Sell CPLD to Xilinx
08/01/1999Philips to Acquire VLSI &nTechnolgoy
05/31/1999Underfill Encapsulant
03/16/2010
