What Is A RF Amplifier, And What Are They Used For?

Broadband RF Amplifier

Within an RF signal chain, there is often the need to provide some signal conditioning in incoming, outgoing, or through signals. One of the most needed signal conditioning methods is amplification of signal energy, which is the key function of RF Amplifiers. Signal amplification involves increasing the amplitude of a signal, this could imply voltage, current, or power amplitude depending on the type of amplifier. In the case of RF amplifiers, typically an RF amplifier’s gain is referenced to the physical concept of power, and given in decibels per watt, or dB.

Power is the physical transition of energy over time, or joules per second (watt). For many consumer wireless applications a watt of RF power is relatively high, though some scientific and defense applications leverage kilowatts of RF power. Within a non-high power signal chain, RF power measured in watts, milliwatts, and microwatts is common. Decibels are a comparative quantity between two measures. Hence, a decibel per watt equates to a logarithmic scale where 0 dB is 1 watt of power, where +/- 3 dB from 0 dB equates roughly to doubling (positive) or halving (negative) the power, respectively.

This concept is important to understanding RF amplifiers as the key parameter for an RF amplifier is gain, which is given in dB. This gain refers to the comparison of the incoming power level to the outgoing power level from a signal injected in the RF amplifiers input compared to the signal exiting the RF amplifier output port. For instance, a 15 dB gain RF amplifier will increase the signal power by 15 dB, or roughly 2x2x2x2x2 = 32 times the original signal power.

RF amplifiers have many limitations, which is where there are varieties of RF amplifier types available, each designed with attributes designed for certain applications or even general performance. One key limitation of an RF amplifier is that the amplifier will increase the power of all signals present at the input as long as they are within the frequency of operation of the amplifier. This includes amplifying noise and interference. Hence, many amplifiers are paired with filters at the input and/or output to minimize the external interference at the input or output of the amplifier. RF amplifiers also add their own internally generated noise to a signal, this is known as added noise. Additionally, RF amplifiers are nonlinear devices that also inject some distortion into a signal, especially if the amplifier is driven close to saturation.