What is the 1 dB compression point?
The 1 dB compression point is the input (IP1dB) or output (OP1dB) power at which an amplifier’s gain has fallen 1 dB below its small-signal value. It marks the onset of significant nonlinearity; OP1dB = IP1dB + G − 1 dB. Saturated output power Psat is typically a few dB above OP1dB.[1][2]
How is P1dB measured?
Sweep input power with a signal generator or the VNA’s power-sweep mode and record gain; P1dB is where gain is 1 dB below the low-power plateau. Use a power meter for absolute accuracy and ensure the source’s harmonics and the receiver’s compression do not corrupt the result.[3]
What sets P1dB?
Supply voltage and bias current (voltage and current swing limits), load line, and device breakdown. For a class-A stage the maximum linear power is roughly (VDD − Vknee)·IDQ/2. Some devices show gain expansion before compression, particularly in class AB.[4]
Why does compression matter for modulated signals?
Compression clips envelope peaks, creating spectral regrowth (ACPR) and constellation errors (EVM). Amplifiers carrying high-PAPR signals are operated backed off from P1dB by several dB, or linearized.[4]
Frequently asked questions
Is P1dB input or output?
Either; datasheets usually give output P1dB for amplifiers and input P1dB for receivers and mixers.
What is P3dB?
The point where gain has dropped 3 dB, sometimes used as a proxy for saturated power.
Can gain increase before compression?
Yes, gain expansion is common in class-AB amplifiers.
See also
References
Online sources accessed October 21, 2026; printed works cited by edition. See all sources.
- “Microwave Engineering, 4th ed.”. D. M. Pozar, Wiley. 2012.
- “RF Microelectronics, 2nd ed.”. B. Razavi, Prentice Hall. 2012.
- “Understanding the Fundamental Principles of Vector Network Analysis (Application Note 1287-1)”. Keysight Technologies. application note.
- “RF Power Amplifiers for Wireless Communications, 2nd ed.”. S. C. Cripps, Artech House. 2006.