P1dB

P1dB, short for the 1-dB compression point, is a standard metric used to characterize the linearity limits of amplifiers in RF, microwave, and related fields. It is commonly defined as the input power level at which the amplifier’s gain falls 1 dB below the small-signal, linear gain. Some datasheets report the corresponding output power, known as the OP1dB or P1dB output. The input- and output-referred definitions are related by the device’s gain in the linear region.

Measurement of P1dB is typically performed at a specified frequency (or within a test band) under a stable bias and temperature. Using a signal generator and power meter, the input power is swept upward while the output is monitored. The IP1dB is determined by extrapolating the linear region of the gain response to the point where the measured gain is 1 dB lower than this linear reference. In practice, a plot of gain versus input power is used to identify the P1dB point.

Interpretation and applications: P1dB marks the onset of significant nonlinear compression and defines the amplifier’s linear dynamic range. It is useful for design decisions related to back-off from saturation to achieve acceptable linearity and to estimate potential distortion performance, such as intermodulation products. P1dB is frequency dependent and can vary with temperature, bias conditions, and device design, so manufacturers specify it under defined test conditions. Higher P1dB values indicate a larger linear operating region before compression.