Freescale Semi

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  • Created: Apr 17, 2015

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Summary

Radio-Frequency power amplifier converts a low power radio frequency signal into a significantly larger signal that is typically used for driving the antenna of a transmitter. Its output power usually measured in kilowatts which can be based on either solid state or vacuum tube technology. Most commercially manufactured linear amplifiers are used in amateur radio that provide between 10 to 20 times RF power amplification. Solid state linear amplifiers are more commonly in the 500 watt range and can be driven by as little as 25 watts.However, this design is a broadcast band RF amplifier that has a frequency response of up to 3MHz. It uses MRFE6VS25LR5 LDMOS transistor featuring a wide operating frequency range and enhanced ruggedness paltform.


The circuit has a frequency response of up to 3 MHz with a gain that is about 30 dB. Field-effect transistor Ql is configured in the common-source self-biased mode; optional resistor R1 allows you to set the input impedance to any desired value. Commonly, it will be 50 . The signal is then direct-coupled to Q2, a common-base circuit that isolates the input and output stages and provides the amplifier`s exceptional stability. Last, Q3 functions as an emitter-follower, to provide low output impedance (about 50 ).If you need higher output impedance, include resistor R8. It will affect impedance according to this formula: Rs ~ ^0lJT - 50. Otherwise, connect output capacitor C4 directly to the emitter of Q3.


This design is used in telecommunication system with frequency range of 1.8MHz to 2000MHz. Its basic applications include driving to another high power source, driving a transmitting antenna, microwave heating, and exciting resonant cavity structures. Among these applications, driving transmitter antennas is most well known. The transmitter–receivers are used not only for voice and data communication but also for weather sensing in the form of a RADAR.

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