P1dBm Vs Voltage Gain dB?

I need 20 dB of Voltage gain 20 log(G)
If the amplifier states

P1dB compresion is @ 19 dBm

does this mean I will go nonlinear at 19 dB ?

I am a little confused

Feel free to pass this question along

Yes, when you see the gain drops down to 19dB from 20dB, P1dB is reached. Nonlinearity increases gradually while Pout approaches saturation power, P1dB is just an indicator of how bad the nonlinearity is.

I think you are more confused than that.

You should realize that there is a big difference between dBm and dB.

dBm is a power ratio. Specifically, it is the ratio of a power measured at a certain point (like the output of an amplifier), to 1 milliwatt.

In other words, if you had 105 milliwatts at an amplifier output, the power could also be stated to be Pout = 10 Log (105 mW/1 mW)= 20.22 dBm

It has almost nothing to do with "gain".

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Gain can be either power gain or voltage gain.

If you have an amplifier and you input 0.1 mW, and at the output you measure 5 mW, you can say it had a power gain of

Gp = 10 Log (5/0.1) = 16.99 dB

If you have another amplifier, and you input 1 volt, and at the output you measure 12 volts into the desired load, then the Voltage gain is

Gv= 20 Log (12/1) = 21.58 dB

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If you are operating well below the compression point of an amplifier, the gains Gp and Gv are constant for varying input power. However, if you get near the compression point of the amplifier, the gain can be smaller (compressed).

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So 19 dBm has nothing to do with the gain (20 dB) of your amplifier, other than to tell you where the amplifier might be compressed.

this means that the gain at 19dBm should be larger than 19 dB ,,,i.e. ouput is larger than 19+19=38dBm

Nooooo. Let try from a different angle.

Lets say I have an amplifier with 20 dB of small signal gain, and a +19 dBm 1 dB compression point. An example might be, with Pin and Pout in dBm, and Gain in dB (power gain):

Pin Pout Gain
-20 0 20
-15 5 20
-10 10 20
-5 14.9 19.9
-2 17.8 19.8
-1 18.5 19.5
0 19 19
1 19.3 18.3
2 19.5 17.5
5 19.6 14.6
10 19.6 9.6