RF Power Amplifier Delivers 2 W and 40 dB Gain From 1500 to 2700 MHz
By Mario Bokatius, Freescale Semiconductor, Inc.
Whether the application is a macro cell or a small cell the ability of an RF power amplifier to provide broad versatility is a highly valuable attribute. For example, if the amplifier can deliver high performance over a wide array of frequency bands used by wireless carriers and can be optimized for each one, it can cost-effectively serve multiple applications within an OEM’s portfolio. This not only allows wide range of products to be created with a minimum of designs but reduces the bill of materials. Freescale Semiconductor has introduced a low-cost InGaP GaAs HBT RF power amplifier housed in a 4x4-pin QFN surface-mount package that is the first such device to deliver 2-W (+33-dBm) and more than 40 dB of gain from 1500 to 2700 MHz.
Freescale's MMZ25333B three-stage RF power amplifier (Figure 1) can be used in a variety of ways, as either a driver or predriver in a macro cell or micro cell base station, or as the final amplifier in a small cell or repeater, for example. It supports any wireless standard and is powered from a single 5-VDC supply. Matching networks on the PC board can be adjusted to optimize the performance of the MMZ25333B at any band within its frequency range. In addition, quiescent bias current is adjustable to provide an optimum combination of linearity and efficiency to meet the requirements of a specific application. It has an integrated single-ended power detector as well.
Virtually all wireless systems today employ a Doherty amplifier architecture in the final amplification stage and are linearized using digital predistortion (DPD) or analog pre-distortion (APD) circuits. The MMZ25333B is well suited for use as a predriver or driver in a Doherty amplifier, and it can be located either on the power amplifier board or on the transceiver board, depending on the design. The device has very high gain, in excess of 40 dB, which can eliminate the need for additional gain stages, reducing the cost and complexity of the circuit.
The Doherty amplifier lineup shown in Figure 2 is typical of a linearized macro or micro cell base station power amplifier. The MMZ25333B acts as the driver amplifier, after which its output is split between the main and peaking amplifiers. In Figure 3, the device is used as a predriver and its output is split between two drivers, which then feed the main and peaking amplifiers. When used as the final-stage amplifier in a non-linearized small cell, the quiescent bias current to the device can be increased to improve its linearity. These are only two of many configurations in which the MMZ25333B can be used.
The MMZ25333B’s combination of very high gain, broad bandwidth, and the ability to be optimized for both the type of amplifier in which it is used and its operating frequency make it highly appealing in a broad array of applications. It is in production and reference designs and other information are available. More information can be obtained at www.freescale.com/RFlowpower.
Freescale Semiconductor, Inc.
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