Measuring the one dB compression point of an amplifier

To avoid oversteering an amplifier it is nice to know the 1dB compression point. That is the input level at which the amplifiers output is 1dB below the level it should be.

Measuring this normally required many measurements at various signal levels. This is a nice challenge for the tinySA.

First part of the setup is the signal generator providing the level sweep. The tinySA setup is below

attachment:dBc_gen.jpg

The frequency is 10MHz and the output level is changing from -40dBm to -10dB over 10.2 seconds

The output the the generator is connected to the input of the amplifier and the output of the amplifier is connected to another tinySA. The second tinySA is in low input mode and set to a zero span mode at 10MHz, a sweep time of 10 seconds and a normal down trigger at a -10dB level as is shown below

attachment:dBc_trig.jpg

When the signal generator jumps back to the -40dB level the second tinySA triggers and starts to record the level over a period of 10 seconds. Using two markers (one reference and one delta marker) it is easy to see the level increase per division is 6dB (5 division with in total 30dB)

attachment:dBc_div.jpg

Then the markers are shifted to the right to a place where the increase is no longer 3dB per half division but only 2dB.

attachment:dBc_comp.jpg

The output 1dB compression level of the amplifier is at marker 2 at 13.8dBm, The input level to the amplifier is at that point -40dB plus 9 times 3dB (or -10 minus 3dB) equals -13dBm. Keeping the input of the amplifier below -13dBm will ensure no compression.


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TinySA-OnedBc (last edited 2020-10-16 14:37:58 by RudolfReuter)