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# ADL5535 1PdB - 1dB Compression Point Unterstanding

Hi Folks,

please could you help me to explain the fact, that the ADL5535 has a higher 1dB compression point than the power supply allows?

Example:

1dB P1 = 18.6dB as lowest in statistic, according to Fig.11. of the datasheet.

18.6dB is 72.44mW into a 50 Ohm load.

U = SQRT (P*R) = SQRT (72.44mW * 50) = 1.9Vrms

Upeak = 1.9Vrms * sqrt(2) = 2.69V

To run Upeak-peak the Voltage swing is: 2 * 2.69V = 5.38V.

This should be the voltage on the 50Ohm termination.

If we consider the internal driver has a 50Ohm series termination, the driving voltage must have 10.77V. Considering no extra headrom for the transistors to drive the load.

How can the outputpowerlevel of at least 18.6dB be explained?

Is the datasheet correct?

Thanks.

• Mehlin,

The Plotted Values of S-Parameters include the test fixture. The tabular values are de-embedded S-Parameters.

• Thank you Jim,
I will double check. The measurements were done in an assembled system (BPF-s before and after the amp.), which has a 680nH inductor instead of the recomended 470nH. I will try to get a separate test panel and re-measure everything according to fig. 25.

• Hi Thomas,

Which brand of inductor is the 680 NH inductor? You should check the SRF of the inductor. If it is below or close to your operating frequency you will allow RF to couple into your power supply thereby reducing the gain and output power. The coilcraft inductor specified in the datasheet has an SRF of 540 MHz. The 680 NH inductor from the same family has a 260 MHz SRF.

• 680nH 0603/0805 inductors have 530/400MHz SRF, so this shouldn't be a problem... But I want to test this too.

• Hi Thomas,
Both inductors look very good. Do you know how much loss the filters have?
Perhaps the issue is filter losses.

inductor.pdf
• Hi Jim!

S21 is 1dB (1.5dB maximum). S11 and S22 of the filters are minimum 15dB in a few MHz passband. that shouldn't be the cause... something less "obvious" is causing the problem, and the problem is there all samples I measured so far.

• Are you factoring for the filter losses in your computation? Maybe the issue is de-embedding. I would suggest isolating the amplifier to do some diagnostic tests.

• I'm using an AWR simulation, measured S parameter filed for the filter, and AD supplied S params for the amp. Impedance mismatches are accounted for. Still no explanation for the huge difference...

I will isolate the amp, when I recive the new PCB, in about 1-2 weeks.