PA Efficiency Calculator
Calculate power amplifier efficiency for all classes — A, AB, B, C, D, E and F. Enter conduction angle, supply voltage and peak current to get output power, drain efficiency, PAE and harmonic content. Side-by-side class comparison table included.
180° < 2α < 360° → Class AB (partial bias)
2α = 180° → Class B (zero bias, IQ = 0)
0° < 2α < 180° → Class C (negative bias)
2α = 0° → Class C limit (no output unless resonant)
Drain efficiency: ηd = Pout / PDC
PAE: = (Pout − Pin) / PDC
PDC = VDD × IDC where IDC = Ipk(sinα − αcosα) / (π(1−cosα))
| Class | 2α | ηd (theory) | Pout (norm) | Linearity | Application |
|---|---|---|---|---|---|
| A | 360° | 50% | 1.00 | Excellent | Linear PA, small-signal |
| AB | 180–360° | 50–78% | 0.5–1.0 | Good | RFPA, base station |
| B | 180° | 78.5% | 0.5 | Fair | Push-pull PA |
| C | <180° | 78–100% | <0.5 | Poor | FM TX, narrowband |
| D | Switch | ~100% | High | Nonlinear | Audio, DC-DC |
| E | Switch | ~100% | High | Nonlinear | HF/VHF PA, ISM |
| F | Switch+harm | ~88% | High | Nonlinear | Microwave PA, RFPA |
Power Amplifier Classes — Design Guide
Power amplifier efficiency is one of the most critical parameters in wireless system design. In a base station PA consuming kilowatts, even a 1% improvement in efficiency saves significant operating cost and cooling. In a handset, PA efficiency directly determines battery life.
Class A — Maximum Linearity
A Class A amplifier biases the transistor at the midpoint of its load line so it conducts for the full 360° of the input cycle. Maximum theoretical drain efficiency is 50% — the transistor always draws current even with no RF input. Class A is used where linearity is paramount: LNA stages, driver amplifiers, and precision measurement equipment.
Class B and AB — The Practical Sweet Spot
Class B biases at pinch-off (zero quiescent current), giving 78.5% theoretical efficiency but with crossover distortion. Class AB biases slightly above pinch-off, trading some efficiency for improved linearity. Most modern RFPA designs use Class AB with digital pre-distortion (DPD) to correct the nonlinearity — allowing base station PAs to operate at 40–50% efficiency with acceptable EVM.
Class D, E, F — Switching PAs
Switching-mode PAs treat the transistor as a switch, theoretically eliminating the I×V overlap that causes dissipation in linear classes. Class E uses a single transistor with a specific reactive load network; Class F adds harmonic traps to shape the drain waveform into a square wave. Practical efficiencies of 70–85% are achievable at RF frequencies.