Linearity Parameters Summary
| Parameter | Definition | Measured How |
|---|---|---|
| P1dB (IP1dB) | Power where gain drops 1 dB from linear | CW power sweep with power meter |
| IIP3 | Extrapolated input intercept of IM3 with fundamental | Two-tone test with spectrum analyzer |
| OIP3 | Output-referred IP3 = IIP3 + G₀ | Derived from IIP3 measurement |
| SFDR | Spurious-Free Dynamic Range | Computed from IIP3 and noise floor |
Relationship Between Linearity Parameters
OIP3 ≈ OP1dB + 9.6 dB (Class A approximation)
OP1dB ≈ OIP3 − 9.6 dB
SFDR = (2/3)(IIP3 − noise_floor) [input-referred]
Cascaded OIP3:
1/OIP3_total = 1/OIP3_N + G_N/OIP3_{N-1} + G_N·G_{N-1}/OIP3_{N-2} + ...
(Last high-gain stage dominates linearity)Back-Off for OFDM Modulation
OFDM signals have high PAPR (Peak-to-Average Power Ratio): LTE 20 MHz: PAPR ≈ 8–10 dB 5G NR 100 MHz: PAPR ≈ 10–12 dB Required PA back-off from OP1dB: Back-off ≈ PAPR + 3 dB (safety margin) ≈ 13–15 dB At +40 dBm OP1dB (GaN PA): average TX power ≈ +25 to +27 dBm
RF View S-Parameter Analysis: RF View analyzes small-signal S21 gain, S11/S22 match, and stability from VNA .s2p files. Combine with bench P1dB and two-tone IIP3 measurements for complete amplifier characterization. Free on Android.