LDMOS RF Driver Transistors Deliver High Performance from 700 to 2700 MHz
By Eric Westberg, Portfolio Manager – RF, Freescale Semiconductor, Inc.
Broadband RF driver transistors provide significant benefits in cellular macro cell designs as they cover all of a wireless carrier’s frequency allocations with a single device. This enables OEMs to reuse significant portions of their RF designs across their entire portfolio. However, while bandwidth is the key metric, a device’s ability to deliver its rated performance characteristics over this wide span truly determines its usefulness. Two new 28-VDC LDMOS RF power transistors in Freescale Semiconductor, Inc.’s Airfast family are tailored to meet these requirements, covering 700 to 2700 MHz while maintaining smooth frequency response, high gain and efficiency, and broad video bandwidth.
Freescale’s new devices are well suited for use as driver amplifiers in 10-W to 40-W macro base stations employing Multiple Input Multiple Output (MIMO), as final-stage amplifiers in small cell and Distributed Antenna System (DAS) transceivers, as well as Industrial, Scientific, and Medical (ISM) and defense communications systems. The devices build on Freescale’s popular MW6S004NT1 4W driver amplifier, which is used throughout the world in 2G, 3G and LTE cellular base stations.
Both the 6W AFT27S006NT1 and 10W AFT27S010NT1 (Figure 1) have high single-stage gain (20 to 24 dB) across their entire frequency range. They are offered in a compact footprint, the PLD-1.5W over-molded plastic package. Key performance characteristics of the devices include:
AFT27S006NT1: 6W P1dB (28.8 dBm average) RF output power, 22 to 24.3 dB gain, 0.05 dB gain flatness, 18 to 22% efficiency.
AFT27S010NT1: 10W P1dB (31 dBm average) RF output power, 21 to 24.3 dB gain, 0.2 dB gain flatness, 21 to 25% efficiency.
Detailed specifications are shown in Table 1.
The ability to serve all wireless bands from 700 MHz to 2700 MHz is very appealing to OEMs as it allows them to use a single RF power transistor as the driver amplifier for their entire product portfolio. This has the obvious benefits of reducing design time and parts count while simplifying amplifier circuits and decreasing overall manufacturing cost. It requires the transistor to deliver uniform performance from the lowest to the highest frequencies in its range, as peaks and dips in performance at certain frequencies negate its ability to serve an entire portfolio.
For this reason, the new Airfast transistors have been characterized by Freescale at four different frequencies: 700, 2100, 2300, and 2600 MHz, and their key performance parameters (gain, efficiency, output peak-two-average ratio, ACPR, and input return loss) for each frequency are provided on the data sheets. Reference designs for each band are provided as well. The characteristics of the AFT27S006NT1 between 710 and 790 MHz and 2480 to 2720 MHz are shown in Figures 2A and 2B respectively and are representative of AFT27S010NT1 performance as well. The plots show measured gain, ACPR, input return loss, drain efficiency and Peak-to-Average Ratio Compression (PARC) when subjected to a 3.84-MHz-wide W-CDMA signal plotted against frequency.
The AFT27S006NT1 and AFT27S010NT1 join the rapidly growing family of Airfast RF power transistors that collectively have significantly greater performance than their predecessors, including 5% higher drain efficiency, 25% higher power density, improved linearity, and broad video bandwidths. The Airfast family also features Freescale’s second-generation, over-molded plastic packaging that provides improved thermal performance and other benefits. All of the reference designs in the Airfast family are validated to provide an optimal combination of efficiency, gain, and linearity in order to accommodate the needs of Digital Pre-Distortion (DPD) circuits.
The AFT27S006NT1 and AFT27S010NT1 are in production and samples are available, along with reference designs at four frequencies. More information is available at
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