hello all,

I try to calculator the NF, using spectre. Comparing with my calculation.

The noise result have the item of input noise, I think it should be the input reference noise. Then I caculator the port source noise, 4KTR,(300k 1.38e-23 50 Ohm), the result is 828z.

However, the (input refer noise)/noise of source, does not equal to the simulator result!

I found spectre use 200z to caculator NF, indeed, Z11 of my circuit is much large than 50Ohm, not at a matching condition, but how to caculator the noise of source on these un-matching conditions?  


And there is also another question, the source noise does not change when temperature change...    Why?  

Please be free to correct my fault in caculation, any suggestion will be very appreciated.

Dear pancho_hideboo,   Thank you for your feedback.

I have several questions in your reply.

First, Andrew Beckett wrote on Apr 14^th, 2010, 4:28pm:

Andrew's opion makes sense I think.  And if you set the noise temperature. The noise of the port is settled, not relative to the Rs of the port. So I do a test, use a attenuator, input port (Rs=200) seriesly connect to 2 resistor, both are 50 ohm, output port(Rl=50) paralle with the last resistor .  However, I found , the NF is not 6dB but 8.88dB. And I try to fill the input port noise temperature, and only this noise temperature is 16.9, the NF=8.88dB.   I am confusing.....








Second, it is correct you mention in another discussed issue

NF is calculated like following.
NF=1+Na/(Gain2*Nin)
here Na=Square of intrinsic output voltage noise from DUT [Vrms2/Hz],
Nin=Square of input voltage noise from source(=4*k*T*Rs) [Vrms2/Hz],
Gain=Voltage Conversion Gain which is the sum of sidebands you have interests in.

I calculated use these equations, I just found the Nin is not equal to (=4*k*T*Rs) in all my LNA designs with matching input and un-matching input.
It seems to be different matching conditions, the source noise power transferred differently to the output.
When Z11 is much larger than input source ressistor, Nin=200z, as you know, 4KTRs(290K 1.38*e-23 50ohm) is 800z.
And in matching conditions, I use (Noise Factor) /(output noise input reference)=Nin=400.4z,output noise input reference is the total noise of output divide by the Gain**2,equivalent to input side, still not 800z. I wonder whether spectre caculated it in these condition(290K 1.38*e-23 50ohm). I did set my simulator under the 27 temperature in ADE, but did not set temerature in port.


Please be free to discuss. Thank you~~

ps  You know, when you use port to do ac analysis, port with 1v ac magnitude,the input of your circuit could get -∞ to 6dB gain. This is because port deliver 1 ac magnitude in matching condition, so total is 2v ac magnitude provide by port. So when Zin big enough to Rs, all 2V is delivered to Zin, so 20log2=6dB. When Zin=0  input only get -∞ gain.
So I mean, using port do analysis, whether it is mathcing,is very important and quite differrent to use vdc (with 1v ac magnitude ) in ac analysis.
Does it the same when do noise? Actually, the noise results in noise analysis is always the same with sp analysis under same condition.