What is the difference between drain efficiency and power added efficiency?
Efficiency Metrics
Drain efficiency is the simplest efficiency metric: how much of the DC power from the supply is converted to RF output. It ignores the RF input power, treating it as free. For a Class A amplifier at maximum output: DE = 50%. For Class B: DE = 78.5%. These are the maximum values assuming zero loss and perfect matching.
| Parameter | LNA | Driver | Power Amplifier |
|---|---|---|---|
| Noise Figure | 0.3-2.0 dB | 3-8 dB | 5-15 dB (not specified) |
| Gain | 10-25 dB | 10-20 dB | 8-15 dB |
| P1dB | -10 to +10 dBm | +15 to +25 dBm | +30 to +50 dBm |
| OIP3 | +5 to +25 dBm | +25 to +40 dBm | +40 to +55 dBm |
| DC Power | 10-100 mW | 0.5-5 W | 5-500 W |
- Performance verification: confirm specifications against the application requirements before finalizing the design
- Environmental factors: temperature range, humidity, and vibration affect long-term reliability and parameter drift
- Cost vs. performance: evaluate whether the application demands premium components or standard commercial grades
- Interface compatibility: verify impedance, connector type, and mechanical form factor match the system architecture
- Margin allocation: include sufficient design margin to account for manufacturing tolerances and aging effects
Frequently Asked Questions
Which should I compare between PAs?
Always use PAE for comparison because it accounts for the gain difference. A PA with 45% DE and 6 dB gain has PAE = 33.75%. Another with 40% DE and 15 dB gain has PAE = 38.7%. The second PA is more efficient despite lower DE because it needs less driver power.
What is total system efficiency?
Total efficiency = Pout_final / (sum of all DC power in all stages). This includes the PA, driver, LO, DPD processor, and supply regulators. Typical total transmitter efficiency: 20-35% for current base station implementations including auxiliary power.
Does efficiency change with output power?
Yes. DE and PAE peak near the compression point and drop rapidly at backed-off power levels. At 10 dB back-off: PAE typically drops to 25-50% of its peak value for Class AB. This is why average efficiency for modulated signals is much lower than peak efficiency.