What is P1dB?

An amplifier usually provides a constant gain over a specific frequency range. If we represent the Input power Vs Output power of an amplifier on a graph, we get a straight line (Linear Relationship) i.e 'output power = input power + Gain' - so if the gain of an amplifier is 10 dB, then a 1 dBm input signal will result in an 11 dBm output signal and a 10 dBm input signal will result in a 20 dBm output signal.

As the input power level increases, there comes a point where the output power of the amplifier no longer increases by the gain value i.e the amplifier output power starts to saturate.

The 1 dB compression point (P1dB) is the output power level at which the gain decreases 1 dB from its constant value. Once an amplifier reaches its P1dB it goes into compression and becomes a non-linear device, producing distortion, harmonics and intermodulation products. Amplifiers should always be operated below the compression point.

P1dB is one of the most important specifications for power amplifiers, as it is up to this point that we consider an amplifier to operate linearly.