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Measurements >> RF Measurements >> DUT noise and gain measurement
https://designers-guide.org/forum/YaBB.pl?num=1194339625

Message started by aaron_do on Nov 6^th, 2007, 1:00am

Title: DUT noise and gain measurement
Post by aaron_do on Nov 6^th, 2007, 1:00am

Hi all,

is there any problem with this test setup?

1) To measure NF we directly measure NF as shown.

2) To measure Gain, we first measure S21 from path 1, then measure S21 from path 2.
Next we measure S11 from path 2.
We can then calculate the voltage gain of the buffer.
Finally we can calculate the voltage gain of the DUT.

Does this seem right? The only assumption is that the capacitance of the output pad is negligibly small. Note that when I measure path 1, the pad at the input of path 2 is open circuit and vice versa.

thanks,
Aaron

Title: Re: DUT noise and gain measurement
Post by pancho_hideboo on Dec 1^st, 2007, 2:27am

Maybe you might already resolve this issues.

If an input impedance of Buffer is known, it is possible to determine voltage gains of DUT and Buffer.
[Note] You can't measure output impedance of DUT correctly even if Buffer is disabled.
This is true for input impedance of Buffer even if DUT is disabled.

You can measure output impedance of Buffer and input impedance of DUT directly.
You can calculate output impedance of DUT from known input impedance of Buffer.
Using these input/output impedances and two S21, you can calculate voltage gains of DUT and Buffer.
[Note] I assume S12 of DUT and Buffer are enough small.

About NF, there is problem in your measurement.
In your NF measurement, NF is affected by Buffer. You have to calibrate this noise from Buffer.
I have no good method about this calibration now.
But if power gain of DUT is enough large and Buffer can be disabled at NF measurement,
your measuremet of NF could be reasonable as NF of DUT.