Freescale Semiconductor is introducing two LDMOS RF devices for final-stage power amplification in Time Division Synchronous Code Division Multiple Access (TD-SCDMA) systems – these are being deployed throughout China and also currently under consideration for other regions.
Designers are being offered a choice between discrete and IC solutions. The MRF7P20040H is an LDMOS FET with 50W peak RF output power; drain efficiency of 43%; 18dB gain at 10W average output power; and air-cavity ceramic package with internal matching for ease of use. The MD7IC2050N is a multi-stage integrated power amplifier IC with 70W peak RF output power; drain efficiency of 35%; 29dB gain at 10W average output power; and on-chip quiescent current temperature compensation with 50Ω on-chip input matching in a moulded plastic package capable of withstanding 225 deg C. Values quoted are typical Doherty performance as measured with a six-carrier, 2025 MHz TD-SCDMA. Both devices are particularly well suited for use in Doherty amplifiers, which are currently used in basestation transceivers to maximise power efficiency.
The new LDMOS devices allow designers to optimise RF power amplifiers to their chosen design, either using a discrete, three-stage PA configuration with the MRF7P20040H as the final amplifier, or using the MD7IC2050N IC (which includes the driver and final amplifier stages) in a two-stage PA configuration.
At the same time Freescale is introducing two reference designs based on Doherty architecture, enabling manufacturers to rapidly create compact, cost-effective, high performance basestation transceiver products for TD-SCDMA networks.
A Doherty amplifier design normally incorporates two amplifiers for different signal amplitude levels, and typically use separate transistors for each amplifier. However, the new devices support a dual-path configuration, which allows a Doherty amplifier to be constructed using a single device rather than two for the final-stage amplifier. In addition, since both devices are inherently broadband, they can operate in both bands allocated for TD-SCDMA (1880 to 1920 MHz and 2010 to 2025 MHz), so that the same device can be used to provide RF power in both bands. These advantages combine to offer the potential for a significant reduction in size, bill-of-materials and circuit complexity for a TD-SCDMA amplifier, while also simplifying inventory management.
The two Doherty amplifier reference designs can significantly shorten the amplifier design cycle. The first design employs the MMG3014N general-purpose amplifier driving the MD7IC2050N to produce a two-stage IC-based amplifier that delivers 35% efficiency at 10W average RF output and a total gain of 45dB. The second design incorporates Freescale's MMG3014N as the pre-driver, the MW6S004N LDMOS FET as the driver and the MRF7P20040H as the final amplifier stage, resulting in a three-stage, discrete-based PA that delivers 38% efficiency at 10W average RF output and 50dB of total gain.