In the 3rd and final part of our series on amplifier additive phase noise testing at Mini-Circuits, we continue our investigation into cascaded amplifiers. Part 2 considered two identical amplifiers in series and four identical amplifiers in parallel. However, we were unable to clearly demonstrate the improvement in 1/f noise provided by the parallel configuration due to equipment noise floor limitations.
In Part 3 we address this limitation by driving the four parallel amplifiers with a single amplifier, all identical, and demonstrate that the cascaded performance is dominated by the single driver amplifier.
We also describe how to best optimize the input power levels into each amplifier in order to avoid regions of high AM-to-PM distortion and achieve optimum performance over a wide bandwidth.

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