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1dB compression point_interpretation

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gaurav_vaidya

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Hello everyone,
i have studied that for a linear system output power should follow the input power. But due to the large signals levels outputs get saturated and the point where the gain drops by 1dB is said to be 1dB compression point.
I have plotted the output power vs input power but i am not able to interpret the graphs .following are the results i m getting for different input signals levels

i/P (dBm) P1(dBin) Gain(dB)
-96 -25.863 30.91
-60 -26.47 30.9
-40 -51 30
-10 7.96 14.43
what does these values signify. Are these acceptable value.how to relate these value with linear or nonlinear system.pls suggest.....
 
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jiripolivka

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Hello everyone,
i have studied that for a linear system output power should follow the input power. But due to the large signals levels outputs get saturated and the point where the gain drops by 1dB is said to be 1dB compression point.
I have plotted the output power vs input power but i am not able to interpret the graphs .following are the results i m getting for different input signals levels

i/P (dBm) P1(dBin) Gain(dB)
-96 -25.863 30.91
-60 -26.47 30.9
-40 -51 30
-10 7.96 14.43
what does these values signify. Are these acceptable value.how to relate these value with linear or nonlinear system.pls suggest.....

The "one-dB compression point" is exactly what it says: as you feed a nonlinear black box with a growing input, the output bends , and where it bends 1 dB down from the straight line, this is your point.
The last line of your table is simply wrong. Your P-1 dB is somewhere above -40 dB input; More input like -10 dB simply drastically overdrives your device.
In saturation, the output does not follow the input and the device only generates harmonics while the desired signal is only distorted.
 

gaurav_vaidya

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The "one-dB compression point" is exactly what it says: as you feed a nonlinear black box with a growing input, the output bends , and where it bends 1 dB down from the straight line, this is your point.
The last line of your table is simply wrong. Your P-1 dB is somewhere above -40 dB input; More input like -10 dB simply drastically overdrives your device.
In saturation, the output does not follow the input and the device only generates harmonics while the desired signal is only distorted.

Thanks a lot jiripolivka,
but i extract is that the maximum signal level that can be tolerate by my amplifier is around -40dBm.So if i specify that my input referred compression point is -51dBm for -40dBm is this makes sense if i talk about linearity. or to i have to go above -40dBm with my circuit
 

jiripolivka

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Thanks a lot jiripolivka,
but i extract is that the maximum signal level that can be tolerate by my amplifier is around -40dBm.So if i specify that my input referred compression point is -51dBm for -40dBm is this makes sense if i talk about linearity. or to i have to go above -40dBm with my circuit

You are close to the truth. Repeat the measurement, and increase the input power to your device in 1-dB steps. Plot the results in a diagram, and extend the straight line you measured for < -40 dBm input. When the output power level gets 1 dB under the straight line, this is exactly P-1 dB OUTPUT compression point.
 

gaurav_vaidya

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Thanks a lot jiripolivka,
with further correction to my circuit I have again done the pss analysis and upto -25dBm my largte signal gain and noise figure remained constant.
and when i plotted 1dB compression point by taking input power extrapolation point taking as -25dBm it come out to be -21dBm(input power extrapolation point).
but i also extracted was that my input power handling capacity is around -21dBm that is (input power extrapolation point).am i right sir
 
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