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Freescale LDMOS RF Power Transistors Optimize Performance of Wireless Base Stations Using Doherty Amplifiers


Seven new devices tailored specifically for signals with high peak-to-average ratios are now available

HONOLULU (2007 IEEE MTT-S International Microwave Symposium) - June 4, 2007 - Freescale Semiconductor today introduced seven LDMOS RF power transistors that deliver exceptional performance and enable WCDMA and CDMA2000 base station transmitters to exploit the full potential of the Doherty amplifier architecture.

Fast becoming an industry standard, the Doherty architecture offers exceptional efficiency but presents design challenges due to conflicting requirements for both high efficiency and high linearity. Designed specifically for the architecture, the new Freescale transistors successfully address these challenges, thereby enabling the creation of base stations that consume significantly less power than those using traditional transistor designs.

Two of the devices operate in the 865 to 960 MHz band, two in the 1930 to 1990 band, and three in the 2110 to 2170 MHz band, covering the most popular cellular, PCS and WCDMA frequencies.

The new devices include:

MRFE6S9205H/HS: 865 to 960 MHz, 58 W average output power, 20.5 dB gain, 34% efficiency, ACPR of -38 dBc (5-MHz offset, 3.84 MHz channel)

MRFE6S9135H/HS: 865 to 960 MHz, 39 W average output power, 20 dB gain, 34.5% efficiency, ACPR of -38 dBc (5-MHz offset, 3.84 MHz channel)

MRF6S19200H/HS: 1930 to 1990 MHz, 58 W average output power, 17.2 dB gain, 29.5% efficiency, ACPR of -38 dBc (5-MHz offset, 3.84 MHz channel)

MRF6S19140HR3/HSR3: 1930 to 1990 MHz, 29 W average output power, 16 dB gain, 27.5% efficiency, ACPR of -51 dBc (885 kHz offset, 30 kHz channel)

MRF7S21170HR3/HSR3: 2110 to 2170 MHz, 50 W average output power, 16 dB gain, 31% efficiency, ACPR of -37 dBc (5-MHz offset, 3.84 MHz channel)

MRF6S21190HR6: 2110 to 2170 MHz, 54 W average output power, 16.4 dB gain, 30% efficiency, ACPR of -38 dBc (5-MHz offset, 3.84 MHz channel)

MRF6S21140HR3/HSR3: 2110 to 2170 MHz, 30 W average output power, 15.5 dB gain, 27.5% efficiency, ACPR of 41 dBc (5-MHz offset, 3.84 MHz channel)

Available on tape and reel, all of the devices operate from a +28 V supply and feature integral ESD protection. They are designed to handle a 5:1 VSWR without damage and are housed in RoHS compliant, high-thermal-conductibility air-cavity ceramic packages.

"The Doherty amplifier's inherent high efficiency can help reduce a base station's annual power consumption when compared to other amplifier types, thus allowing Freescale to deliver to our service provider customers the least costly product to operate," said Gavin P. Woods, vice president and general manager of Freescale's RF Division. "But to achieve its full potential, Doherty amplifiers require RF power devices specifically tailored for their needs. Freescale is the first company to deliver these Doherty-optimized, high-efficiency power devices, which are designed from the ground up to make the most of this unique type of amplifier architecture."

The Doherty challenge
The Doherty amplifier has unique characteristics that enable extremely high efficiency. When properly designed, it can deliver efficiency increases of 11 to 14 percent when compared to standard parallel Class AB amplifiers that are traditionally utilized in wireless base station transmitters. At the 2007 IEEE MTT-S International Microwave Symposium, Freescale will present a paper during Thursday's IMS TH3A-02 session describing a 900 MHz Doherty amplifier utilizing Freescale's latest MRF6ES9205H.

A Doherty amplifier consists of two amplifiers - carrier and peaking - operating under vastly different conditions. The RF power transistors in Doherty amplifiers must provide excellent output impedance matching under both linear operating conditions in which the RF drive level of the carrier amplifier is "backed-off" to ensure high linearity and efficiency, as well as during peak (maximum) signal conditions handled by the peaking amplifier. In creating the seven new LDMOS devices, the challenge for Freescale was to optimize the device structure and output impedance matching to accommodate both types of signal conditions, while also satisfying the needs of the Doherty architecture itself.

It is possible to employ RF power devices in Doherty amplifiers that have not been optimized to satisfy its unique requirements. However, to provide top performance, the devices must be created specifically for use in applications with high peak-to-average ratios such as Doherty amplifiers. Freescale chose this more difficult approach, overcoming related challenges to deliver the best combination of efficiency, linearity, and impedance matching for Doherty amplifiers of any RF power devices in the industry.

Availability
The seven new LDMOS devices introduced by Freescale are now sampling. Data sheets and a Doherty reference design are available from Freescale for evaluation purposes. For specific pricing information, contact Freescale Semiconductor, a local Freescale sales office or a Freescale authorized distributor.

About Freescale Semiconductor
Freescale Semiconductor is a global leader in the design and manufacture of embedded semiconductors for the automotive, consumer, industrial, networking and wireless markets. The privately held company is based in Austin, Texas, and has design, research and development, manufacturing or sales operations in more than 30 countries. Freescale is one of the world's largest semiconductor companies with 2006 sales of $6.4 billion (USD). www.freescale.com

Freescale Media Contacts:

North America
Jack Taylor
Freescale Semiconductor
(512) 996-5161 Office
(512) 560-6197 Mobile
jack.taylor@freescale.com

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