[Question]Noise figure measurement of LNA
high impedance node and not be matched to 50 ohms?
In my LNA design, I used LC tank to be the load, so the LC tank will be looked
as high impedance at operating frequency.
But, how to do the noise measurement, because the loading of NF meter will
degrade the gain of LNA.
Any one has experience on this?
You can use an impedance matching circuit from high impedance to 50 ohms. An RF transformer may be sufficient for your need. The matching circuit (or transformer) may introduce some loss but will only give a minor degradation of the noise figure if the gain is high. What is the operating frequency, gain, expected noise figure?
300MHz, 30dB voltage gain, and 2dB NF.
But can the transformer deal the impedance from 2k to 50 ohms?
Well, i agree that a transformer is required.
Of course, to be accurate, the Available gain of the transformer should be known and taken in account.
But, i woul'd move your attention to the effect that DUT cause when it will be placed in front of a system.
The overall NF, using the Agilent 57-1 nomenclature, is F12=F1+(F2-1)/G1, where G1 is the available gain and F2 is the noise figure of 2nd stage when the 2nd stage see Zo (i.e. 50 Ohm) at the input.
Now, if the Z is very far from 50 Ohm the actual value of G1av anf F2 are very far from the measured.
You should expect that the actual F12 is far (read higher) than calculated F12