What is power-added efficiency (PAE)?

From RF Design Wiki · By the RF Design Wiki editorial team · Published October 21, 2026 · Last reviewed October 21, 2026 · How we research

Drain (or collector) efficiency is η = P_out/P_DC. Power-added efficiency subtracts the drive power: PAE = (P_out − P_in)/P_DC = η(1 − 1/G). PAE penalizes low-gain stages; at 10 dB gain, PAE is 90% of drain efficiency.^[1]

Why does efficiency drop in back-off?

In class B, efficiency falls in proportion to output voltage amplitude: η = (π/4)·(V_out/V_max), so at 6 dB back-off it halves to about 39%. Class A efficiency falls in proportion to output power. Signals with high PAPR spend most time well below peak, so average efficiency is much lower than peak.^[1]

What techniques improve back-off efficiency?

Doherty: active load modulation; peak efficiency at back-off. See Doherty amplifier.
Envelope tracking: supply voltage follows the envelope.
Outphasing (Chireix): two constant-envelope signals combined with varying phase.
Load modulation balanced amplifiers and dynamic biasing.

^[1]^[2]

What other efficiency metrics are used?

Overall transmitter efficiency including DPD and supply modulators, average efficiency for a given signal PDF, and system-level energy per bit. Base stations commonly report line-up efficiency at specified average power.

Frequently asked questions

What is a good PAE?

It depends on frequency, technology and linearity; handset PAs commonly reach tens of percent at rated power.

Why does PAE include input power?

To avoid crediting a stage for power supplied by its driver.

Does DPD affect efficiency?

DPD lets the PA run closer to saturation, improving efficiency, but costs DSP power.

References

Online sources accessed October 21, 2026; printed works cited by edition. See all sources.

“RF Power Amplifiers for Wireless Communications, 2nd ed.”. S. C. Cripps, Artech House. 2006.
“A New High Efficiency Power Amplifier for Modulated Waves”. W. H. Doherty, Proceedings of the IRE, vol. 24, no. 9, pp. 1163-1182. September 1936.

Categories: Amplifiers

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