What is the difference between a GaN and a GaAs power amplifier and when do I use each?
GaN vs GaAs PA Technology
GaN (gallium nitride) and GaAs (gallium arsenide) are the two dominant III-V semiconductor technologies for RF power amplifiers. They differ fundamentally in their material properties: GaN has a wider bandgap (3.4 eV vs 1.42 eV), higher breakdown field (3.3 MV/cm vs 0.4 MV/cm), and higher electron saturation velocity. These material advantages translate directly to device-level performance differences.
| 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 |
Bias and Operating Point
GaN's high breakdown voltage allows operation at 28-50V drain voltage, compared to 3-12V for GaAs. This higher voltage means the same output power requires lower current, reducing I²R losses and simplifying the output matching network (higher impedance transformations). A single GaN transistor can deliver 10-100W at cellular frequencies, whereas GaAs typically maxes out at 5-10W per device.
- 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
Stability Considerations
GaAs maintains advantages in noise figure (especially at mmWave frequencies where GaAs pHEMTs achieve 1-2 dB NF vs 1.5-3 dB for GaN) and in per-unit cost for moderate power applications. The GaAs industry has decades of reliability data and established manufacturing infrastructure, while GaN reliability models are still maturing.
Frequently Asked Questions
Which is more efficient?
At the same output power: GaN achieves 5-10% higher PAE than GaAs because the higher voltage operation reduces the impact of the knee voltage on efficiency. GaN Doherty PAs achieve 50-60% average PAE for LTE; GaAs Doherty achieves 40-50%. For switched-mode amplifiers, GaN's higher voltage and faster switching further increase the efficiency advantage.
What about cost?
GaAs costs less per die ($0.50-5 for a PA die). GaN on SiC costs more ($2-20) due to the expensive SiC substrate and smaller wafer sizes. However, GaN's higher power density means fewer devices are needed for a given output power, often making the total PA module cost competitive or lower for high-power applications.
When does GaN-on-Si become viable?
GaN-on-silicon substrates are much cheaper than GaN-on-SiC but have poorer thermal performance (silicon has 4× lower thermal conductivity than SiC). GaN-on-Si is viable for moderate power (<10W) applications at sub-6 GHz, including 5G small cells and WiFi. For high power and mmWave, GaN-on-SiC remains necessary.