This is the second part of a two-part blog series dedicated to providing a brief explanation of the various types of RF amplifiers with highlights of pertinent applications. This section includes more specialty amplifier types that are still widely used throughout the RF/microwave/millimeter-wave industries.
Gain Block Amplifier (GBA)
Gain block amplifiers are much like broadband amplifiers, except they are generally designed to input and output higher power levels than broadband amplifiers. Moreover, GBAs tend to have higher gain than broadband amplifiers, and may not necessarily be broadband, though many GBAs are broadband. A GBA is more often used in the transmission signal chain, where added noise isn’t as much of a concern as with the reception signal chain.
Limiting Amplifier
A limiting amplifier is a type of amplifier that includes additional circuitry and features that prevent the amplifier from outputting signal energy beyond a designed threshold. This is particularly useful in circumstances where the input of a sensitive circuit element must be limited below a certain amount to avoid damage or desensitization. For instance, limiting amplifiers are often used in receiver signal chains where the receive circuitry is sensitive to input signal energy level.
Linear Amplifier
A linear amplifier is a power amplifier that is specifically designed to exhibit linear input/output characteristics. Like other PAs, a linear amplifier’s purpose is to add gain to relatively high power level signals, with the added nuance that a linear amplifier’s performance is optimized for linearity over other considerations. Test and measurement, along with some sensing applications, often require highly linear power amplifiers to avoid distortions that would reduce the performance of the system.
Variable Gain Amplifier (VGA)
A variable gain amplifier (VGA), or variable gain control amplifier, is a type of amplifier where the gain can be adjusted from a minimum to maximum range. VGAs are used in applications where the output signal power needs to be controlled or the input signal level is unknown but there are limitations on the acceptable output power.
Hi-Rel Amplifiers (Hi-Rel Amps)
Though not often considered part of the basic RF amplifier variations, Hi-Rel Amplifiers are crucial for modern defense and government applications where the survivability and environmental ruggedness of a power amplifier (PA) are as crucial as the gain and power handling capability of the amplifier. Generally, Hi-Rel RF Amplifiers are designed to meet military standards, such as MIL-STD-202 and MIL-STD-810, which ensure reliable operation on extremely demanding conditions. The entire design of Hi-Rel amplifiers is driven by the need to withstand shock, vibration, exposure to harsh/caustic environments, and operate over a wide temperature range without sacrificing frequency, bandwidth, gain, or linearity performance.