Please can you help by providing the voltage conversion gain for the ADL5382 with a 50 ohm differential output load.
ADL5382 output stage behaves as a voltage source with a 50 ohm impedance (see datasheet p13 Emitter Follower Buffers), and the change in gain can be computed from the voltage divide ratio between the source resistor and the load resistance.
Voltage Conversion Gain on p3 is defined as 3.9 dB into 450 ohm at 900 MHz.
As an example, if the input is 0 dBm or 0.632Vpp (50 ohm RF input) into ADL5382 then the output is
Vopp=10^(3.9/20)*0.632 = 0.99Vpp into 450 ohm.
To compute the output voltage into 50 ohm, we can first calculate the open circuit output voltageVs(open) = 0.99 * (450 + 50)/450 = 1.1 VppVopp (50) = Vs(open) * Rload/(50 + Rload) = 1.1* 50/(50 + 50) = 0.55 Vpp into 50 ohm
The Voltage Conversion Gain into 50 ohm is then 20*log(0.55/0.632)= -1.2 dB
I am confused by the ADL5382 voltage conversion gain. I understand the conversion gain definition 20LOG(V0/Vin). But the output of ADL5382 has two channel (I and Q), then the conversion gain is 20LOG（V0/sqrt（I^2+Q^2））?
Is this right?
ADL5382 power gain is Vgain+10LOG(Rin/RL). We should use impedance transformer , if the load differential impedance is 500 ohm. Is this correct?
Thanks for the answer to my first question. I've done some more testing on the ADL5382 eval board and have another question regarding the device conversion gain into a 50 ohm baseband load.
I have noticed that the conversion gain/loss changes with input RF level, which is not mentioned anywhere on the data sheet. In my test the LO was a 950 MHz 0 dBm CW signal and the RF was a CW signal at 950.5 MHz. The resultant I and Q outputs are a 500 kHz sinewave terminated in a 51 ohm differential load. At an RF input level of -30 dBm the voltage gain is -0.32 dB and at -5 dBm input I measure -1.75 dB.
I'm prepared to accept the -1.75 dB result as close enough to the predicted values of -1.2 dB if you factor in the 51 ohm load error, but I don't understand the result at lower RF input level of -0.3 dB. Any thoughts on where my measurement may be going wrong or is this the true performance of the device?
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