wirelessZONE Products for the week of July 2, 2007

Freescale Semiconductor Says . . .
MRFE6S9205H: LDMOS RF Power Transistors Optimize Performance For Basestations Using Doherty Amplifiers
Seven devices tailored for signals with high peak-to-average ratios are now available

Freescale Semiconductor 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)

EN-Genius Says . . .

One day in 1936, William Doherty was on the Staten Island Ferry on the way to work in Western Electric's Bell Laboratories, in New Jersey, when he had a moment of genius. He had been working on high power senders (transmitters for you non-RF people) for transoceanic traffic and the efficiencies they were achieving were lousy. (This must make him one of the first green engineers as well!) He suddenly saw a solution in using one power amplifier for gain up to one level of signal, and then a second (inverted) to amplify the upper part of the signal. He sketched the system in the marging of his newspaper.

With quarter-wave delay lines for phasing, the system proved to be brilliant, and the twenty-nine year old won a number of awards. By 1940 Western Electric had numerous senders in service with up to 50 kW input power.

More than fifty years later the Doherty amplifier is back in favor for cell systems, to improve the efficiency of the increasingly more expensive power bills at basestations. With DSPs and other controls, implementation today of the Doherty architecture is dramatically simpler than in 1940 but the devices in the amplifier need to be optimized for the application. Enter Freescale with this family of parts.

To me the volume device of interest here is the MRFE6S9205H.

It would have been nice to see a data sheet but, unfortunately, the absolutely awful Freescale web site refused to yield one up. But, summarizing, these are all 28 V devices with the output power of the 9205H at 58 W average. That actually hardly ties up with the quoted drain quiescent of 1.4 A… The 1 GHz device is fully matched on-chip and can handle a 10:1 VSWR load. The output match for Doherty use is absolutely critical. Power gain is 20.5 dB while drain efficiency is 34%. 5-MHz offset ACPR is -38 dBc in a 3.84 MHz channel bandwidth.

This whole family will do extremely well, with Doherty, logically, very much back in fashion. The seven LDMOS devices are in air cavity ceramic packages. Pricing has not been disclosed.

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