Is P1dB the maximum output power for an RF power amp?

[skatefast08]

Is P1dB the same as maximum output power or max power dissipation on a transistor datasheet? Or can p1db vary significantly with max output power? Looking to make class AB RF power amplifier.

 

[frankrose]

1dB compression point is where the linear power gain drops 1dB of the matched amplifier because of distortion.

Point sometimes marked as equivalent max. input power, or max. output power. Both depend on supply value, transistor operating point. So it can vary.

But it is not the maximum power which the transistor can dissipate. It is the maximum power where its gain is still linear.

 

[skatefast08]

But it is not the maximum power which the transistor can dissipate. It is the maximum power where its gain is still linear.

If a class A amplifier ideally can dissipate 25% of the power to RF power and I look in the datasheet for the transistors max dissipation power is 300 mW, this should mean I would ideally get 75 mW at the output, right? Couldn't I then get 75 mW (18.75 dBm) as a typical value for the P1dB parameter listed on a transistor datasheet (ex. ATF-55143), or maybe higher than this (wouldn't make much sense if it could though)?

Another thing that confuses me is why do LNA transistors have a P1dB specification shown and power transistors dont have that specified?

 

[frankrose]

If a class A amplifier ideally can dissipate 25% of the power to RF power and I look in the datasheet for the transistors max dissipation power is 300 mW, this should mean I would ideally get 75 mW at the output, right?

I am not sure about 25%, sounds too low, but class A efficiency is smallest.

Couldn't I then get 75 mW (18.75 dBm) as a typical value for the P1dB parameter listed on a transistor datasheet (ex. ATF-55143), or maybe higher than this (wouldn't make much sense if it could though)?

I don't understand exactly your point, but your transistor P1dB is measured at 14.4dBm output power, 2.7V supply. Its max. power is 24dBm, max. supply is 5V, so you can increase the supply to reach higher P1dB if you keep dissipation under maximum.

Another thing that confuses me is why do LNA transistors have a P1dB specification shown and power transistors dont have that specified?

To filter harmonics in power amplifiers is essential, "easy" and/or most of them operates in Class C,E, where point is the efficiency, not clear, undistorted signals.
But at LNAs the filtering cannot prevent blocker/interference signals and it is very tough to amplify a very small signal next to other very high interference. Interferences cause gain drop for the desired signal because of compression, and harmonic products can ruin receiving also.

 

[BigBoss]

A-Class Amplifiers have ideally %50 Efficiency.It's practically %30-35.
P_1dB Compression point is not the limit of the Available Power from an Amplifier.P_3dB is also used for very High Power Amplifiers.
P_SAT is also a Definition Point.It's effectively variable and depended on the definition.

 

[biff44]

P1db is kind of like the tachometer redline in a sports car
Pmaximum is more commenly called Psat, is going beyond redline, where smoke starts to billow out of the exhaust on said car.