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Dual-path RF transistors save cost in TD-SCMDA amps

Posted: 26 May 2010 ?? ?Print Version ?Bookmark and Share

Keywords:RF transistor? amplifier? TD-SCDMA? network?

Freescale Semiconductor has developed two LDMOS RF power transistors optimized for power amplifiers in base stations serving TD-SCDMA wireless networks.

The MRF8P20160HSR3 transistor and MRF8P20100HSR3 device are fabricated using Freescale's latest High-Voltage Eighth Generation LDMOS technology. Both devices are inherently broadband, so they can deliver rated performance over both frequency bands (1880MHz to 1920MHz and 2010MHz to 2025MHz) allocated for TD-SCDMA operation, which allows a single device to serve both bands.

The amplifiers in TD-SCDMA base stations employ the Doherty architecture, which consists of two amplifiers that together accommodate most operating conditions. This typically requires separate RF power transistors in the carrier and peaking paths of the final stage of the power amplifier. However, Freescale's LDMOS transistors are "dual-path" designs in which both amplifiers required to implement a Doherty final stage amplifier are integrated within a single package. This reduces the required number of devices by half. These benefits, together with high gain and efficiency and low power consumption, allow TD-SCDMA amplifiers to be fabricated at a low cost, with few components and reduced complexity.

The MRF8P20160HSR3 features 37W average output power (160W CW at P3dB compression), 45.8 percent drain efficiency, 16.5dB gain and -30.6dB ACPR (3.84MHz channel bandwidth at 5MHz offset) measured with an input signal peak-to-average ratio of 9.9dB. Meanwhile, the

MRF8P20100HSR3 offers 20W average output power (126W CW at P3dB compression), 44.3 percent drain efficiency, 16dB gain and -33.5dB ACPR (3.84MHz channel bandwidth at 5MHz offset) measured with an input signal peak-to-average ratio of 9.9dB.

Both devices operate from a 26V to 32V supply, can handle a voltage standing wave ratio of 10:1 at 32Vdc, and are designed for use with digital predistortion error-correction circuits. They are internally matched, housed in air cavity ceramic packages, and available on tape and reel. The devices also incorporate protection from the ESD encountered on assembly lines. ESD protection also enables a broad swing in gate voltage from -6V to +10V that enhances performance when operating in high-efficiency modes such as Class C.

The advanced devices join Freescale's current family of RF LDMOS power amplifiers for TD-SCDMA operation, including the MRF7P20040H LDMOS FET and MD7IC2050N multi-stage integrated power amplifier IC, which each deliver 10 W average power over both TD-SCDMA bands.

The MRF8P20160HSR3 and MRF8P20100HSR3 are in full production now. A reference design and other support tools are also available now.

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