Power Added Efficiency
Understanding PAE
PAE captures both the RF gain and the DC-to-RF conversion efficiency of an amplifier in a single metric. It reaches maximum near compression and drops off at lower power levels (where the amplifier is linear) because the DC consumption remains relatively constant while the output power decreases.
Efficiency Metrics Compared
- Drain efficiency: eta_D = P_out / P_DC. Does not account for input power. Overstates efficiency for low-gain stages.
- PAE: (P_out - P_in) / P_DC. Accounts for input power. More accurate for low-gain amplifiers.
- Wall-plug efficiency: P_out / (total AC input power). Includes power supply losses.
PAE by Technology
| Technology | Typical PAE | Frequency |
|---|---|---|
| GaN HEMT | 40-70% | 1-40 GHz |
| LDMOS | 40-60% | 0.1-4 GHz |
| GaAs pHEMT | 30-50% | 1-100 GHz |
| SiGe HBT | 20-40% | 1-30 GHz |
| InP HEMT | 15-30% | 30-300 GHz |
For high-gain amplifiers (Gain >> 1):
PAE approximately equals drain efficiency
For Gain = 10 dB:
PAE = 0.9 x drain efficiency
For Gain = 3 dB:
PAE = 0.5 x drain efficiency
Frequently Asked Questions
What is PAE?
PAE (Power Added Efficiency) is the percentage of DC power converted to added RF power: PAE = (P_out - P_in)/P_DC x 100%. It is the most complete single-number efficiency metric for RF amplifiers because it accounts for the input signal power.
Why is PAE important?
For battery-powered devices, satellite transponders, and cellular base stations, PAE directly determines DC power consumption, heat dissipation, and battery life. Even small PAE improvements save significant operating costs in large-scale deployments.
How do you maximize PAE?
PAE peaks near compression. For maximum PAE, operate the amplifier near P1dB. However, this conflicts with linearity requirements for complex waveforms. Digital pre-distortion (DPD) enables near-compression operation while maintaining linearity.