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On the Marki website the APM6848 (bare die or module) is showing phase noise plots with a +9dBm and +12dBm input.

The part with a +5v supply is specified to reach saturation typically with a +4dBm input.

Do you have any PN data with a +4dBm input, +5V power supply, carrier at 3GHz?

 

Also, are the PN plots in the datasheet residual PN or absolute PN?

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The answer is no we don’t for the frequency and/or power they are asking for.  These are residual phase noise measurements, so we had a lot of trouble finding a condition where we were able to get clean data that wasn’t pushed into the noise floor of the measurement.  The reason we used 6V on these measurements was because we had to use batteries to power the DC power supply to clean up the measurement enough, and so we ultimately had to chain 4 1.5V batteries together.

 

One of the goals that we have in the near term future is to populate our data with more information about phase noise performance vs. input power.  Subsequently, we would like to be able to have some experimentation about the phase noise vs. frequency, but this is much harder to do comprehensively because of limitations of the phase noise system we have currently, and the amount of frequency-specific filtering and isolation that is needed to make clean reliable measurements at each specific frequency point.

 

Based on what we have seen, the phase noise performance is not linked very strongly with frequency.  I would not expect the phase noise to be much better or worse at 2.5 GHz than it is at 4 GHz or 8 GHz.  Where I expect it will begin changing is if you are moving to a high enough frequency that you are getting higher levels of compression at some similar input power.  To first order, Enrico Rubiola shows experimentally that phase noise performance is somewhat independent of frequency on page 12 of “Phase Noise in RF and Microwave Amplifiers”.

 

The question about variation with input power is a tough one, primarily because of the difficulty in measuring reliable clean residual phase noise data for very clean low phase noise amplifiers.  The question of the relationship between HBT amplifier compression and phase noise performance is one we really want to answer.  Our understanding based on the literature and data we have seen is that in HEMT and FET amplifiers, there is a significant degradation in phase noise performance as the amplifier enters high compression (likely due to AM-PM conversion).  We would expect a similar relationship in HBTs, but we didn’t see that trend clearly when we were running our own experiments.  We also found some evidence in the literature from the second paper attached that the trend isn’t quite as strong in HBT amplifiers as they are in FET amplifiers.  (See the final page of Jason Breitbarth’s paper “Additive Phase Noise in Linear and High-Efficiency X-Band Power Amplifiers”).

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