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Volume 60 (Nov 13, 2006)
RF Devices by NEC Electronics can control distortion and power consumption in wireless LAN transmissions
The emergence of "hot spots"
At a table sits a businessman checking his e-mail and surfing the net on a notebook PC. Until recently, this scene was primarily observed in hotel lounges. With the rise in the number of wireless LAN areas referred to as "hot spots," however, PC users now can access the Internet free of charge at train stations, airports, libraries and even fast-food restaurants.
Along with the increasing prevalence of wireless LAN environments, it is now commonplace for notebook PCs, handheld game consoles and other such devices to come equipped with wireless transmission functions. In fact, shipments of wireless LAN chip sets in 2005 increased by more than 50% compared to the previous year, and are expected to nearly triple by 2009.
Challenges facing wireless LAN technology: Distortion and power consumption in RF devices
Wireless transmission of information is conducted using specified frequencies (Figure 1). For example, mobile phones use bands ranging from 800 MHz to 2 GHz, whereas a wireless LAN uses a 2.4 GHz band, which is an even higher frequency band than that used by mobile phones.
The radiowave system for wireless LAN has been standardized in accordance with the IEEE 802.11 standard developed by the Institute of Electrical and Electronics Engineers, Inc. Under the IEEE 802.11b standard, the maximum data-transfer rate for the 2.4 GHz band is 11 Mbps, while that under the IEEE 802.11g standard is 54 Mbps. At this transmission rate, both voice and video transmissions are possible, and the transmission range is approximately 100 m.
A new modulation method has recently come into use for wireless LAN. Referred to as orthogonal frequency division multiplexing (OFDM, hereafter referred to as the OFDM modulation method), this method can be used to prevent crossing of signals as well as enable effective use of radio waves. For increased accuracy in the transmission of large volumes of information when using this modulation method, transmission devices require a feature referred to as "distortion" that makes it possible to maintain the accuracy of transmission signals. For example, distortion in the amplifier (power amp) of a transmission device can be controlled using a device with high output power at a low output level to maintain the accuracy of the signal. In other words, satisfactory linearity can be obtained. However, when output power rises, so does electric power consumption. In this way, RF devices such as power amps are not only sought after for their ability to control distortion, but also for the extent to which they can control power consumption, which could be said to be the fate of mobile devices.
NEC Electronics power amps and switches for wireless LAN use
As the leader in RF devices, NEC Electronics has long offered a diverse lineup of RF devices such as power amps, low-noise amps and switches for use in mobile phones, satellite broadcasting receivers and more. Using the technologies we have developed thus far, we have put together a product lineup that includes power amps and antenna switch ICs for wireless LAN use (Figure 2).
The µPG2315T5T has been commercialized as a wireless LAN power amp. The greatest strength of our company's power amps lies in their superior transistor performance. Since the independently developed gallium-arsenide heterojunction bipolar transistor technology (hereafter referred to as GaAsHBT) uses a semiconductor junction that differs from a bandgap, excellent high frequency characteristics such as distortion control can be realized with low power consumption. And by making use of this GaAsHBT technology, the industry's lowest level of power consumption, 130 mA, can be realized when output is 63 mW in the 2.4 GHz band under the wireless LAN (IEEE 802.11g) standard. In addition, the distortion index referred to as error vector magnitude (EVM) is important in the case of the OFDM modulation method, and a modulation accuracy of EVM 3% can be attained when output is at 63 mW with the µPG2315T5T. In terms of the package, the µPG2315T5T comes equipped with the industry-standard 16-pin QFN package, thereby enabling both mounting area reduction and standard installation. And since the inside of the package is based on a heatsink construction, stable characteristics can be realized even under high temperatures.
As for the transceiver section of terminals compatible with wireless LAN, the µPG2164T5N has been commercialized as a high-frequency, gallium-arsenide, double-pole, double-throw (DPDT) switch capable of conducting transmission and reception switching as well as diversity antenna switching. NEC Electronics' antenna switch technology is based on heterojunction field-effect transistor (HFET) technology, which has been cultivated over the years as a satellite broadcasting reception device technology. Taking advantage of our past experiences and achievements, we were able to bring to reality a switch with low RF signal transmission loss. And since the µPG2164T5N reduces transmission loss by approximately 40% according to in-house calculations (0.5 dB (typ.) at f = 2.5 GHz, 0.7 dB (typ.) at f = 6.0 GHz), it contributes to the reduction of both power consumption by the power amp and noise during receipt. Moreover, thanks to the use of the industry's smallest package, mounting area is reduced by 75% and thickness by 50% (both according to in-house calculations), thus creating a compact and low-profile product.
The release of a product family for use with Bluetooth wireless technology
Like wireless LAN, Bluetooth is a short-distance wireless communication technology. Operated in the 2.4 GHz ISM band, it has been standardized for use with a vast array of devices. For example, in addition to being used in wireless headphones and handheld game consoles, Bluetooth technology supports the realization of hands-free functions for mobile phones, MP3 players and more.
It is generally possible to construct Bluetooth Class 2 transmission systems that support a 10-meter transmission range with a single silicon IC. However, to construct a Class 1 system that has a transmission distance of 100 meters and beyond, a power amp must be included in addition to the silicon IC. Our lineup therefore includes the µPG2314T5N, a Bluetooth Class 1 power amp IC. This power amp IC makes it possible to realize a low power consumption level of 65 mA during 100 mW output and comes equipped with the same 6-pin TSON package as the µPG2164T5N, thus making it both compact and low profile.
The µPG2314T5N is used in the reference design of the CSR BlueCore4-ROM, which is made by CSR, a major Bluetooth chip set manufacturer headquartered in Cambridge, England (Photo 1, Figure 3).
The future of wireless LAN
Since microwave ovens are operated at nearly the same frequency as the 2.4 GHz band used for wireless LAN, it is expected that utilization of a dual-band multi-input multi-output (MIMO) as well as a 5.0 GHz band enabling even faster communications will become the norm for preventing interference while using microwave ovens and meeting growing needs for video transmission and more.
NEC Electronics is working toward the realization of more highly integrated power amplifiers, independent development of ultra-compact packages and the development of products to meet next-generation wireless LAN and Bluetooth needs. In addition, in accordance with the growing sophistication of both technologies, we are strengthening the compatibility of our products with reference designs offered by major chip set manufacturers.
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