RF PA
An RF PA accepts a low-level (typically 0–10 dBm) modulated RF input and delivers a high-power (typically 1 W to several kW) replica into a 50 Ω antenna load with controlled linearity, efficiency, and harmonic content. Examples: Skyworks SKY77352-21 cellular PA, Qorvo TQP9314 GaN PA, NXP A2T35S160 LDMOS broadcast PA.
An RF PA stage usually consists of one or more transistors (LDMOS, GaN HEMT, GaAs HBT) biased into class-AB, class-F, or Doherty configurations with carefully tuned input/output matching networks. For high-PAR signals such as OFDM, envelope tracking dynamically adjusts the PA's drain supply to follow the signal envelope, keeping the device near saturation only when the envelope demands it — boosting efficiency from class-A's 25 % to 50 % or more without compressing peaks.
In plain terms
A megaphone for radio: the speaker (modulator) only whispers into the megaphone, but the megaphone projects the voice across a stadium (the RX 100 km away) — and the megaphone has to add power without distorting the voice's accent (the modulation).
Why designers use it
- Reach distant cellular base stations with enough EIRP for reliable handset uplink.
- Drive Wi-Fi 6E and 5G NR antennas at the EIRP regulators allow without violating ACLR masks.
- Transmit kilowatts from broadcast and satellite uplink stations using paralleled GaN modules.
- Power radar transmitters that have to put kilowatts on a single pulse for adequate target return.
Best for
- Cellular TX
- Wi-Fi TX
- Broadcast TX
Key specifications
- Operating limits: Check the exact manufacturer's datasheet (A family name does not establish voltage, current, temperature or timing limits.)
- Pin assignment: Match the complete part and package code (A similar name or function does not guarantee the same wiring.)
- Mechanical fit: Use the exact package drawing (Check pad layout, dimensions and viewing direction before building.)
When not to use it
- When the link is short and a +10 dBm transmitter suffices (BLE-Mesh) — a discrete PA wastes power and adds an EMC failure mode.
- Where regulators forbid amplification of a passive radio (RFID readers in the EU) — bypass and reduce TX gain instead.
Common mistakes
- Driving an OFDM signal into a class-AB PA without backing off below P1dB — the PAPR clips, ACLR fails the regulatory mask, and the receiver sees raised noise floor in adjacent channels.
- Skipping the harmonic filter at the PA output — second and third harmonics violate the FCC out-of-band emission limits and a single product passes regulatory test by accident, then fails an audit.
Where you will find it
- An iPhone's main 5G NR PA module (Qorvo QM77024 or similar) uses GaAs HBT cells in a Doherty configuration with envelope tracking: it delivers +27 dBm peak output for n78 (3.5 GHz) uplink while holding ACLR < −37 dBc and achieves > 40 % power-added efficiency — without ET, the PA would heat the phone unacceptably fast and battery life would halve.
- A Wilson Pro 1100 cellular signal booster uses an NXP LDMOS PA to take −80 dBm cellular signals from a building's outdoor donor antenna, amplify them by 70 dB, and re-radiate them indoors at +27 dBm: the LDMOS PA preserves the cellular waveform's modulation across LTE, 5G, and 3G simultaneously, all at the same time.
- A SiriusXM satellite-radio uplink ground station drives a 12 GHz GaN PA at 200 W per polarisation: the PA pushes the QPSK-modulated content uplink to satellite SR-XM through a 9-metre dish, with the GaN's high-temperature operation tolerating the sustained CW output that would melt earlier silicon LDMOS PAs.
A short history
An RF power amplifier raises a radio-frequency signal to the power needed at a transmitter's output. Matching networks couple the amplifier to its load, and filtering can reduce unwanted harmonics. Preserving the desired modulation depends on the amplifier's operating mode and linearity, rather than being automatic for every power amplifier.