Two new laterally diffused metal-oxide silicon (LDMOS) RF power transistors from Freescale Semiconductor enable wireless basestation amplifiers to cover all channels in an entire allocated frequency band. These devices should help reduce capital and operating expenditures and increase network flexibility in amplifier systems.

Most of today’s amplifier systems operate with bandwidth limitations of 20 to 40 MHz, which necessitates a separate power amplifier (PA) for each channel. However, increasing wireless data traffic is driving a trend to extend amplifier systems to cover entire wireless frequency bands.

Freescale’s latest LDMOS RF power transistors combine high linearity, high efficiency, wide instantaneous bandwidth, and high power to extend the instantaneous signal bandwidth to an amazing 160 MHz, making them ideal for these next-generation amplifier systems.

The MRF8P20165WH/S targets the 1930- to 1995-MHz PCS band (see the figure). The MRF8P20140WH/S fits the 1880- to 2025-MHz TD-SCDMA bands A and F. Both can support the corresponding wireless spectrum with one amplifier. This significantly reduces the number of PAs needed for a multiband basestation and enables network operators to consolidate devices and equipment, resulting in lower operating expenditures.

The wide instantaneous bandwidth of these devices increases network flexibility for network operators by allowing network equipment sharing between operators and by simplifying upgrades. Operators can add or exchange spectrum holdings within a frequency band without upgrading equipment.

Also, because wideband/multiband PAs are generally agnostic to modulation formats, operators can upgrade to 4G Long-Term Evolution (LTE) and other wireless standards with a simple software change and no additional hardware. This means network operators save on both capital and operating costs. Operators also can reconfigure channels on the fly and apply channel consolidation to support increased data rates.

The MRF8P20165WH/S and MRF8P20140WH/S meet the linearity requirements for the PCS and TD-SCDMA standards while delivering efficiency of at least 43.7% when amplifying multiple wireless carriers separated by up to 65 MHz (PCS) and 140 MHz (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.

Key specifications for the MRF8P20165WH/S (1930 to 1995 MHz) include 37-W average power with input signal peak-to-average ratio (PAR) of 9.9 dB, 47.7% drain efficiency, and 16.3-dB typical power gain. Specifications for the MRF8P20140WH/S (1880 to 2025 MHz) include 24-W average power with input signal PAR of 9.9 dB, 43.7% drain efficiency, and 16-dB 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 voltage standing-wave ratio (VSWR) impedance mismatch when operating at 30 V and driven with twice their recommended input power.

The transistors also are internally matched with low capacitance to simplify circuit design. Their integrated electrostatic discharge (ESD) protection makes them more resistant to stray voltage encountered on assembly lines. In addition, their broad gate-source voltage range of –6 V to +10 V increases their performance when operated in Class C mode.

The MRF8P20165WH/S and MRF8P20140WH/S are available in sample quantities. Full production is expected after May 2011. A reference design and other support tools are available to designers.

Freescale Semiconductor
www.freescale.com