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ADL5205

First, is there a Keysight Genesys system model for the ADL5205?  I downloaded the latest .zip from ADI but I don't see that part listed when I install the Genesys v20 files.

Second, On my eval board, I see the nearly 26 dB voltage gain (13 dB power, minus balun losses).  The attenuator, however controls the level in 1 dB steps in power, not voltage.  This is confusing.  The amplifier is spec'd as dB voltage gain, but the attenuator moves in dB power?

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  • Anyone have any thoughts on attenuator spec'd in dB Power, with amplifier spec'd in dB Volts?

  • Because the voltage gain is defined as 20*log(U.out / U.in) and power gain is defined as 10*log(P.out / P,in) there is no difference in case the impedances are matched.

  • Yes, Thanks.  Working with opamps, I think in voltage gain, but working with RF devices, I think in power gain- this is why I am confused.  But the part schematic shows 0 to 23 dB from the attenuator and 14 to 26 dB from the amplifier.  On the eval board (which has Z matching baluns), if I apply a fixed power level, and step the device's gain setting inputs, I measure power gain from +11 to -24 dB (the 35 dB range claimed by the data sheet, including 2 dB balun losses).  So I have to conclude that the attenuator settings (which control both the attenuator and the VGA) are 10*log(Pout/Pin) or dB Power steps, while the amplifier is spec'd as voltage gain.  So the amplifier offers 13 dB gain in power.

    This would all make sense, but the voltage codes for gain in the data sheet say the steps are voltage gain in dB, but it appears the steps are power gain in dB.

  • I have looked the schematic of the EVB, the input and output impedance is 50Ohm, voltage and power gain SMA input - SMA output are identical. I attach short calculation for max gain:

    -1dB (input balun1:2) +26dB (max gain of ADL5202) -12dB (fixed atten 220Ohm to 50Ohm) -1dB (output balun 1:1) = 12dB (EVB max gain)

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  • Thank you Viktor for pointing this out.  I completely overlooked the output resistor network.  I replaced the resistors and balun with a 1:5 transformer and I get a power gain of 29 dB as well as 35 dB of power control as in the data sheet.

    The 10 ohm output impedance is pretty much resistive at low frequency where I am using the device, so the transformer seems like a good solution.