The green movement and the continuing quest to lower operating expenses puts an increased focus on the RF power amplifiers in basestations. Improved efficiency while maintaining linearity is the goal. Freescale’s MRF8S9260H, MRF8S9170N, MRF8S9200N, and MRF8S9300 laterally diffused metal oxide semiconductor (LDMOS) power transistors are designed with that in mind.

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These devices specifically target WCDMA and multicarrier GSM basestation amplifers. They also suit Long-Term Evolution (LTE) and WiMAX amplifiers. Operating over the 860- to 960-MHz range, they can be used in class AB or C configurations. Based on Freescale’s eighth-generation high-voltage (HV8) LDMOS process technology, the four transistors can provide a power output range of 100 to 300 W.

The family suits top-of-the-tower amplifiers and multicarrier applications. Designers can save huge amounts of power in basestations by putting the power amplifers (PAs) on top the tower with the antenna. This eliminates the huge losses in the transmission lines that force operators to use more power than necessary. Because of wind loading, space, and safety issues, though, top-of-the-tower designs don’t fit all installations.

Efficiencies can also be gained in GSM basestations that now use one PA per GSM carrier. With a broadband higher-efficiency PA, up to six or eight GSM carriers can be amplified simultaneously in a single broadband PA with a bandwidth up to 20 MHz.

The MRF8S9260H, which can be used in multicarrier GSM applications, offers 58-dBm (630 W) peak power and 16.3-dB gain. Its drain efficiency is 42.5% at an average output power level of 49.4 dBm (87W) with good broadband linearity. Typical operating supply voltage is 28 to 32 V. The devices have been optimized for use in a Doherty amplifier configuration. A Doherty amplifier uses two devices effectively in parallel. One operates continuously, and the other phases in or out depending upon power output needs. The Doherty design improves efficiency and provides good linearity over a wide bandwidth. Freescale offers a Doherty reference design.

The MRF8S9170N and MRF8S9200N target lower-power applications and feature a low-cost over-molded plastic package. The MRF8S9300 has greater power capability and comes in a ceramic package.

The MRF8S9260H is an N-type enhancement-mode MOSFET housed in an air-cavity ceramic package. Typical power gain is 19 dB with 36% efficiency and 75-W output.

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