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Design >> RF Design >> 1dB compression point
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Message started by gaurav vaidya on Apr 4^th, 2012, 5:43am

Title: 1dB compression point
Post by gaurav vaidya on Apr 4^th, 2012, 5:43am

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 power(dBm) P1in(dBm) 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 they acceptable value.how to relate these value with linear or nonlinear system.pls suggest.....

Title: Re: 1dB compression point
Post by RFICDUDE on Apr 5^th, 2012, 4:54pm

All active circuits behave in a nonlinear manor at some point. Every active device circuit has a finite power supply voltage or a point where the signal swing is large enough to cause the output current to cut off. When this happens the output will no longer follow the input in a purely linear manor.

Amplifier linearity is characterized by the 1dB compression point (input/output amplitude where the gain has dropped by 1dB from the small signal gain). There are two-tone amplitude modulated tests to further characterize the linearity, but the gain compression test is relevant to your question.

Title: Re: 1dB compression point
Post by gaurav vaidya on Apr 9^th, 2012, 4:56am

Thanks a lot RFICDUDE,
what i add to my knowledge is that If my input power is -40dBm , then my input extrapolation point will be equal to -40dBm and the values that come at that point will be my input /output referred compression point.
Am i right. For example from my readings for -40dBm input referred compression point comes out to be -51dBm.
but can from this value can i talk some but about how much my system is linear or non linear or i have to perform two tone test.

Title: Re: 1dB compression point
Post by aaron_do on Apr 9^th, 2012, 5:50pm

Hi,

are you sure you ran your simulation correctly? I have a hard time visualizing how you could have extrapolated an IP1dB of -51 dBm when the reference gain is at an input of -40 dBm (are you sure the result is not -21 dBm?).

You should extrapolate from a point where you know the gain is linear. So even if you change the extrapolation point by a few dB, it shouldn't change the IP1dB result. Anyway P1dB is just a reference point and is very subjective. It doesn't necessarily signify that anything significant has happened at that point. For instance, just because the IP1dB is -10 dBm, it doesn't mean that the system can't run beyond -10 dBm, and it doesn't even mean that the system can work up to -10 dBm. Furthermore, just because amplifier A has an IP1dB of -10 dBm and amplifier B has an IP1dB of -8 dBm, it doesn't mean that amplifier B will work up to a higher input power.

regards,
Aaron