What is the difference between OIP3 and IIP3 and when do I use each specification?
OIP3 vs IIP3 Usage
Using the correct IP3 reference is essential for accurate system calculations. A common error is mixing IIP3 and OIP3 in the cascade formula, which leads to grossly incorrect results.
| 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 |
- 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
Frequently Asked Questions
What if the datasheet only gives one?
Convert using the gain: IIP3 = OIP3 - Gain, or OIP3 = IIP3 + Gain. Use the S21 (small-signal gain) for the conversion. The gain used should be the small-signal gain (not the compressed gain).
Which is typically larger?
For devices with positive gain (amplifiers): OIP3 > IIP3 (by the gain amount). For devices with loss (passive mixers, filters, attenuators): IIP3 > OIP3 (or IIP3 = OIP3 for lossless passives). For unity-gain devices: IIP3 = OIP3.
Does temperature affect OIP3 and IIP3 equally?
Temperature primarily affects the transistor nonlinearity. Both OIP3 and IIP3 degrade at high temperature (typically 0.5-2 dB degradation per 25°C increase). The gain also changes with temperature (typically -0.02 dB/°C for GaAs, -0.01 dB/°C for GaN). Since OIP3 = IIP3 + Gain: the OIP3 degradation includes both the nonlinearity degradation and the gain change.