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What should be paid attention to when testing P1dB?

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Author : AmpliVsionS
Update time : 2021-02-03 11:24:03

Non-linearity is a topic that cannot be avoided by RF active devices such as PA and LNA. Although it is inevitable, it is still hoped to keep it as low as possible to reduce the impact on the system. There are many parameters to measure nonlinear characteristics, and the 1dB gain compression point is usually a must-test item.
 

 Psat,P1dB and Power consumption of power amplifier system AVBR2060U50


What should be paid attention to when testing P1dB?
 
First of all, the power-on sequence of the amplifier must be correct, especially the power amplifier. For GaAs and GaN amplifiers, most of them are currently designed with depletion transistors. When the gate-source voltage is 0V, it is open. Therefore, the gates of these amplifiers generally work in a negative voltage state. For this type of amplifier, for protection purposes, the negative gate voltage must be added first, and then the drain voltage.
 
Secondly, when testing the PA, it is necessary to select an appropriate attenuator according to its maximum output power, so as not to burn the RF front end of the spectrum analyzer if the power is too high. The internal attenuator of the spectrum analyzer can usually only withstand the power of 1W at most, so the power after the external attenuator must be much smaller than this value.
 
Finally, considering the test accuracy, a suitable attenuator can be introduced before and after the amplifier to improve the input and output matching. For the PA test, due to certain requirements on the driving power, the attenuation before the PA should not be too large, and it is necessary to ensure that the power of the signal source after the attenuator can still drive the PA to work normally.
 
In addition, it is necessary to prevent the spectrum analyzer from entering the non-linear region. You can refer to the spectrum analyzer's specification to find its P1dB. As long as the power fed into the spectrum analyzer is at least 6dB below this value during the test, the nonlinearity of the spectrum analyzer itself The impact can be ignored.
 
There is also a simple judgment method. When the 1dB compression point is found, manually increase the attenuation of the spectrum analyzer. If the measured signal power is basically unchanged, then the spectrum analyzer has no obvious nonlinearity; if the attenuation is increased, If the measured power increases instead, it means that the RF front-end of the spectrum analyzer has been compressed. It is necessary to further increase the attenuation until the measured power is stable, and then continue to increase the output power of the signal source to find the true 1dB compression point of the amplifier.

 

             Psat,P1dB and Power consumption of power amplifier system AVBR2060U50