2500MHz Linear Amplifier using MMA25312BT1 InGap HBT
Created: Apr 22, 2015
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Ideally, an amplifier is said to be linear if the input power is proportionally related to the output power by the gain of the amplifier. In an RF amplifier design, linearity is a very important parameter to be considered since it determines the fidelity of the signal. High amplifier linearity is possible, but at the expense of efficiency. One of the classic trade offs in power amplifier transistors is between output power and bandwidth. Active devices are inherently limited in bandwidth by internal capacitance. Eventually, every transistor reaches a frequency at which signal gain drops below unit and where the device is no longer useful as an amplifier. Smaller transistor geometries can achieve higher operating frequencies, but the smaller dimensions result in reduced power capacity.
The reference design as shown is a linear amplifier that uses a Freescale MMA25312BT1 InGap heterojunction bipolar transistor (HBT). The MMA25312B is a 2-stage high efficiency InGaP HBT driver amplifier designed for use in 2400 MHz ISM applications; WLAN (802.11g), WiMAX (802.16e) and wireless broadband mesh networks. It is suitable for applications with frequencies from 2300 to 2700 MHz using simple external matching components with a 3 to 5 V supply. The advantages of InGap heterojunction bipolar transistor include superior reliability, less temperature sensitivity, lower turn on voltage, lower leakage current and excellent linearity. These are the reasons why it is very suitable for linear amplifiers.
Linear amplification is very useful in a wide variety of applications including Wireless Communication, TV transmissions, Radar, and RF heating. It is also very important when the signal contains AM – Amplitude Modulation or a combination of both, Amplitude and Phase Modulation (SSB, TV video carriers, QPSK, QAM, OFDM).