Select the RF amplifier family from the stage's job in the signal chain, not from the largest gain or power number. Fix the input and output reference planes and complete operating band first. Then reject families that cannot meet the required noise, linearity, output, control, supply, mechanical or thermal boundary.
Use this decision order:
- Low-noise amplifier (LNA): use near a receiver input when cascaded noise figure and sensitivity dominate; also verify blocker tolerance, input survivability, stability and gain.
- Gain block: use for predictable fixed gain and broadband 50-ohm integration when moderate noise and output performance are acceptable.
- Driver amplifier: use when the next stage needs a defined drive level; compare output P1dB or OIP3, gain flatness, stability and maximum input.
- Power amplifier: use for the final delivered RF output; define average and peak power, waveform, back-off, efficiency, heat removal, mismatch and protection.
- Variable-gain amplifier: use when closed-loop level control or dynamic-range management is required; include gain range, step or control law, settling time and linearity at every gain state.
Do not compare unlike conditions. Gain, noise figure, P1dB, IP3 and efficiency are meaningful only with frequency, bias, temperature, load, waveform and reference plane stated. Reject a candidate when full-band data, maximum-input behavior, mounting boundary or production acceptance evidence is missing.
Before requesting a model, provide: operating and guard bands; minimum and maximum input; required gain and flatness; average and peak output; PAPR plus EVM, ACPR or IMD limit; CW, pulsed or modulated duty; source/load VSWR; supply and control; ambient or baseplate temperature; cooling, outline, connectors, quantity and qualification needs.