What is power added efficiency and how do I maximize it in a transmitter design?
PAE Optimization
PAE is the most meaningful efficiency metric for power amplifiers because it accounts for the input drive power, which can be significant for high-gain devices. For a device with 15 dB gain, the input power is 3.2% of the output power, making PAE nearly equal to drain efficiency. For a device with 6 dB gain (common at mmWave), the input power is 25% of the output, and PAE is significantly lower than drain efficiency.
| Parameter | Class A | Class AB | Class F/Doherty |
|---|---|---|---|
| Max Efficiency | 50% | 50-78% | 70-90% |
| Linearity | Excellent | Good | Moderate (needs DPD) |
| P1dB Backoff | 0-3 dB | 3-6 dB | 6-10 dB |
| Complexity | Low | Low | High |
| Common Use | Test, small signal | General PA | Base station, broadcast |
Frequently Asked Questions
What PAE should I target?
For cellular base stations: 40-55% at average power (with DPD/Doherty). For handsets: 35-45% at max power. For satellite: 40-60% (critical for power budget). For radar: 50-70% at peak power (efficiency at average may be lower).
Does the matching network affect PAE?
Yes. A matching network with 0.5 dB insertion loss reduces the effective PAE by approximately 10%. Output matching networks should use high-Q components and low-loss substrates. At mmWave, matching loss can consume 1-2 dB, significantly impacting PAE.
How does Doherty improve backed-off PAE?
Doherty maintains high PAE at 6-10 dB backoff by using load modulation. At average power (6 dB backoff), conventional Class AB PAE is about 15%; Doherty PAE is 40-50%. This is the primary advantage for modulated signals with high PAPR.