As is well known, the 1dB compression point, or P1dB, is the power level where the output power of a device, such as an amplifier, starts to drop off from the linear input/output power curve, and reaches a point where the actual output power is 1 dB less than the theoretical linear curve. In other words, the gain is 1 dB less than the small-signal gain.
So, for instance, let's say the gain of our amplifier is 10 dB. At an input power level of -10 dBm, the output power level would be 0 dBm. At an input power level of 5 dBm, the linear output power would have been 15 dBm, but in reality it is 14 dBm. This leads to the following values for our amplifier:
Input P1dB = 5 dBm
Output P1dB = 14 dBm
Or does it?
About 10 year ago I was told by an Analog Devices support person that the definition of Output P1dB, as used on your datasheets, refers to the ideal output power at that point, and would be 15 dBm in the example above. Since then I have been subtracting 1 dB from all the Output P1dB values on your datasheets to reflect the actual output power at that point.
I thought it was time to confirm whether that person from 10 years ago told me the truth.
1. Do you indeed define Output P1dB to be 15 dBm in the example above?
2. What about the former Hittite parts? How is Output P1dB defined on their old datasheets? Are their Output P1dB values adjusted by adding 1 dB to them when the datasheets are converted to AD datasheets?