RF amplifiers are electronic devices that accept a varying input signal and produce an output signal that varies in the same way as the input, but that has larger amplitude. RF amplifiers generate a completely new output signal based on the input.

Depending on load of the output circuit, one or more RF pre-amplifiers may boost the signal and send the stronger output to a RF power amplifier (PA).

Other types of RF amplifiers include:

• Low noise
• Pulse
• Bi-directional
• Multi-carrier
• Buffer
• Limiting amplifiers
• Detector log video amplifiers (DLVAs) are used to amplify or measure signals with a wide dynamic range and wide broadband.
• Successive detection log video amplifiers (SDLVAs) are log amplifiers that can operate over a wider dynamic range than DLVAs
• Extended range detector log video amplifiers (ERDLVAs) are DLVAs that can operate with a wider operating frequency.  

Selection Criteria

Operating frequency is the frequency range for which RF amplifiers meet all guaranteed specifications.

Design gain, the ratio of the output to the input power, is normally expressed in decibels (dB), or G_db = 10 * log (P_o/P_i).

Output power is the signal power at the output of the amplifier under specified conditions such as temperature, load, voltage standing wave ratio (VSWR), and supply voltage.

Gain flatness indicates the degree of the gain variation over its range of operating wavelengths.

Secondary performance specifications to consider include:

• Noise figure (NF)
• Input VSWR
• Output VSWR
• Monolithic microwave integrated circuit (MMIC) technology

The noise figure, a measure of the amount of noise added to the signal during normal operation, is the ratio of the signal-to-noise ratio at the input of the component and the signal-to-noise ratio measured at the output. The NF value sets the lower limit of the dynamic range of the amplifier. Input VSWR and output VSWR are unit-less ratios ranging from 1 to infinity that express the amount of reflected energy.

Video Credit: AR Modular / CC BY-SA 4.0

Specifications

There are several physical and electrical specifications to consider when selecting RF amplifiers.

Package Type

• Surface mount technology (SMT)
• Flat pack
• Through hole technology (THT)
• Connectorized
• Waveguide assemblies

Connector Type

• BNC
• MCX
• Mini UHF
• MMCX
• SMA
• SMB
• SMP
• TNC
• Type F
• Type N
• UHF
• 1.6 / 5.6, and 7/16.

Electrical Characteristics

• Nominal operating voltage
• Nnominal impedance

Operating Temperature

Operating temperature is an important environmental parameter to consider.

Standards

EIA TEP 138 - Noise figure testing of RF amplifier tubes

MIL-A-27821 - Amplifier group, radio frequency

MIL-A-28875/1 - Amplifiers, radio frequency and microwave, solid state

References

Image Credits: Digi-Key Corporation | Newark / element14 | MilesTek Corporation