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LDMOS transistors cover full frequency for wireless stations

Posted: 03 May 2011 ?? ?Print Version ?Bookmark and Share

Keywords:LDMOS? transistors? wireless stations?

Freescale Semiconductor introduces two LDMOS RF power transistors that allow wireless base station amplifiers to cover all channels in an entire allocated frequency band. The company claims that these high-efficiency transistors help reduce capital and operating expenditures, and their wide instantaneous bandwidth allows operators to increase network flexibility.

Most of today's amplifier systems operate with instantaneous (video) bandwidth limitations of 20C40MHz and require a separate power amplifier for each channel. However, increasing wireless data traffic is driving a trend to extend amplifier systems to cover entire wireless frequency bands. Freescale's new RF power LDMOS transistors deliver a combination of high linearity, high efficiency, wide instantaneous bandwidth and high power that extend the instantaneous signal bandwidth to 60MHz, making them ideal for these next-generation amplifier systems.

Freescale's MRF8P20165WH/S for the 1930 to 1995MHz PCS band and the MRF8P20140WH/S for the 1880 to 2025MHz TD-SCDMA bands F & A can support the corresponding wireless spectrum with one amplifier. This significantly reduces the number of power amplifiers needed for a multiband base station and enables network operators to consolidate devices and equipment, resulting in lower operating expenditures.

In addition, the wide instantaneous bandwidth of Freescale's new LDMOS devices increases network flexibility for network operators by allowing network equipment sharing between operators and by simplifying upgrades. Operators can add/exchange spectrum holdings within a frequency band without upgrading equipment, and because wideband/multiband PAs are generally agnostic to modulation formats, operators can upgrade to 4G LTE and other wireless standards with a simple software change and no additional hardware. Operators also can reconfigure channels and apply channel consolidation to support increased data rates.

"The need for RF power transistors to deliver exceptional linearity and efficiency over a full wireless band is no longer simply desirable; it is essential," says Ritu Favre, vice president and general manager of Freescale's RF division. "The devices we are introducing today are the first in a family of broadband RF power transistors that includes all current and emerging wireless bands. Each device will be designed to combine all of the attributes C high efficiency and linearity and high output powerC required to allow carriers to meet the challenges of the future."

Freescale's MRF8P20165WH/S and MRF8P20140WH/S meet linearity requirements for PCS and TD-SCDMA standards while delivering efficiency of at least 43.7 percent when amplifying multiple wireless carriers separated by up to 65MHz (PCS) and 10MHz (TD-SCDMA). Both devices are dual-path designs, and can implement the final stage of a Doherty amplifier with one path as the main amplifier and the other as the peaking amplifier.

The key specifications of the new RF power LDMOS devices are as follows:

MRF8P20165WH/S (1930 to 1995MHz)
???37W average power with input signal peak-to-average ratio (PAR) of 9.9dB
???47.7 percent drain efficiency
???16.3dB typical power gain

MRF8P20140WH/S (1880 to 2025MHz)
???24W average power with input signal PAR of 9.9 dB
???43.7 percent drain efficiency
???16dB typical power gain

Both devices are designed for use in Doherty amplifier configurations and digital pre-distortion. They are extremely rugged and can handle a 10:1 VSWR impedance mismatch when operating at 32V and driven with twice their recommended input power. The transistors are internally matched with low capacitance to simplify circuit design and have integrated electrostatic discharge (ESD) protection that makes them more resistant to stray voltage encountered on assembly lines. In addition, their broad gate-source voltage range of -6 to +10V increases their performance when operated in class C mode. The transistors are housed in Freescale's NI-780-4 and NI-780S-4 air cavity packages.

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