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.


 

  • I'm also facing the same problem, and the datasheet is definitely incorrect... I'm still waiting for an official answer from Analog.

    According to my measurements, P1dB is around 9dBm, and Psat is 13.5dBm (@5V, @160MHz). I hope it helps...

  • This is just a guess, but if the P1dB is specified for a conjugate match to the device output and the real part of the output impedance is less than 50 ohms, then the power output would be correspondingly higher. Looking at the values for S22 provided in the datasheet, it looks like that could be the case. If thomasww is taking his measurements in a 50 ohm system and not matching the output, this might also explain his results.

  • The datasheet states "Input and output internally matched to 50 Ω", so I've naively connected the input to a matched source and the output to an Agilent spectrum analyzer directly, and the measured results are:

    However, I will run some simulations to check if the "not so 50 ohm" matching could cause the difference...

  • Based on S22 from the datasheet at 1000Mhz, it looks to me like the real part of the output impedance for the ADL5535 is 31.5 ohms, with a reactance of -4.9 ohms. I have to admit to being a little confused here since the S-parameters are apparently in dB format and the the tabular values for S22 magnitude do not seem to correspond to the plotted values for return loss in the datasheet, particularly at the lower frequencies.

  • My measurements were done az 160MHz, as I wrote before. According to an AWR simulation, the S parameters do not explain the missing dB-s in my case... So I'm still saying, something in this datasheet is definitely wrong.