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Simulators >> RF Simulators >> How to caculator the noise of the input source
https://designers-guide.org/forum/YaBB.pl?num=1275297742

Message started by ranger_hyz on May 31^st, 2010, 2:22am

Title: How to caculator the noise of the input source
Post by ranger_hyz on May 31^st, 2010, 2:22am

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. ::)

Title: Re: How to calculate the noise of the input source
Post by pancho_hideboo on May 31^st, 2010, 3:17am

I can't find out any design issue in your post.

Your questions are no more than very easy usage of very specific vendor's simulator.

ranger_hyz wrote on May 31^st, 2010, 2:22am:

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

Turn off noise from output load or port.

ranger_hyz wrote on May 31^st, 2010, 2:22am:

I found spectre use 200z to caculator NF

Show me your situation in detail and correctly.

http://www.designers-guide.org/Forum/YaBB.pl?num=1239925339/4#4

ranger_hyz wrote on May 31^st, 2010, 2:22am:

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?

Nothing special is required for evaluation of NF. Unmatching is very general.

http://www.designers-guide.org/Forum/YaBB.pl?num=1214890959/2#2
http://www.designers-guide.org/Forum/YaBB.pl?num=1237656418
http://www.designers-guide.org/Forum/YaBB.pl?num=1194006190

ranger_hyz wrote on May 31^st, 2010, 2:22am:

the source noise does not change when temperature change... Why?

It is true for Agilent ADSsim.
But it is not true for Cadence Spectre.

http://www.designers-guide.org/Forum/YaBB.pl?num=1190112138
http://www.designers-guide.org/Forum/YaBB.pl?num=1192525133
Read only my appends since others are all wrong.

Title: Re: How to caculator the noise of the input source
Post by ranger_hyz on May 31^st, 2010, 8:25pm

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:

You should use pnoise with a probe as the output, pointing at the port. The whole point is that the port is part of the measurement equipment (think of how you'd do the measurement on the bench), and so the noise produced by the termination is not part of the noise in the circuit.

Similarly, the noise produced by the input port is at whatever temperature is set on the port via the noisetemp parameter - rather than what the simulation temperature is. That's because the input port is not on the chip, and so wouldn't be at the same temperature as the chip - it should be producing a known amount of noise..

Using a voltage as the output for pnoise is fine if you are computing noise figure, and there's nothing in the circuit which represents the loading of the "probe" - maybe you have a voltage rather than power output. It's also OK if you're not computing noise figure, but (say) output noise.

Not really a design issue - would have made more sense in the RF simulation board.

Hope that helps,

Regards,

Andrew.

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..... :-X

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.

Title: Re: How to calculate the noise of the input source
Post by pancho_hideboo on Jun 1^st, 2010, 3:12am

Your questions are very easy and very common issue in RF community.

But many RF beginners who have experience of only EDA-Tool-Play but no experience of actual measurement often have same confusions as yours.

Learn measurements using actual instruments. Not "EDA Tool Play.

Surely read the followings again.
http://www.designers-guide.org/Forum/YaBB.pl?num=1239925339/4#4

http://www.designers-guide.org/Forum/YaBB.pl?num=1214890959/2#2
http://www.designers-guide.org/Forum/YaBB.pl?num=1237656418
http://www.designers-guide.org/Forum/YaBB.pl?num=1194006190

http://www.designers-guide.org/Forum/YaBB.pl?num=1190112138
http://www.designers-guide.org/Forum/YaBB.pl?num=1192525133

ranger_hyz wrote on May 31^st, 2010, 8:25pm:

Andrew's opion makes sense I think.

No. Temeperature of noise source is very important for NF measurement.
Surely read http://www.designers-guide.org/Forum/YaBB.pl?num=1192525133/16#16

ranger_hyz wrote on May 31^st, 2010, 8:25pm:

The noise of the port is settled, not relative to the Rs of the port.

Very wrong.
It is true only for available noise power of port.

ranger_hyz wrote on May 31^st, 2010, 8:25pm:

However, I found , the NF is not 6dB but 8.88dB.

|S21| is not -6dB in your case.

ranger_hyz wrote on May 31^st, 2010, 8:25pm:

It seems to be different matching conditions, the source noise power transferred differently to the output.

It depends on what definition you use for voltage gain.
Consider definition of Gain you apply.

http://www.designers-guide.org/Forum/YaBB.pl?num=1237656418

ranger_hyz wrote on May 31^st, 2010, 8:25pm:

Does it the same when do noise?

No, it is not same.

Do you understand a definition of "IRN" when using port not vsource as input signal ?

Show me netlist you use.