Hi all,


by definition, NF must be quoted at 290K however, most receivers are designed to operate over a broad temperature range. So what is the convention for defining NF at different temperatures? I'm asking because i was writing a paper and one of the reviewers pointed out that it is incorrect to define NF away from 290K...he didn't offer any alternative however...


thanks,
Aaron

Thanks for the link

that makes me question though, in spectre, if we simulate NF versus temperature, is the source temperature taken as 290K or the operating temperature when calculating NF?

thanks,
Aaron

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

Hi.

ENR table is defined as noise ratio of Tcold(290K) and Thot.
But actual temeperature(Tambient) is not 290[K].
So user have to compensate of temperature difference from 290[K].
Default value of Tambient is 296.5[K] not 290[K] in actual instruments such as
Agilent N8974A or N8975A Noise Figure Analyzer.
These NF analyzer have a temperature sensor built in a noise source, so Tcold can be auto corrected.

In legacy NF meter such as Agilent 8970B, there is no auto correction for Tcold.
Unless user enter temperature of Tambient, NF meter assume Tambient is 290[K].

Anyway actual NF meter with correct setting calculates NF as T0=290K regardless of Tambient.
If this is corresponded to simulation(e.g. Cadence Spectre), port temperature is 290[K],
analysis temperature is Tambient.

http://cp.literature.agilent.com/litweb/pdf/5952-3706E.pdf

It is also important to realize that the temperature that is needed for noise figure is the temperature of the source not the temperature of the circuit. The temperature of the source is the temperature of the channel, and 290 is probably a reasonable approximation to that.

-Ken

Hi.

"1+Te/Tphys, the ambient temperature Tphys" is wrong.

Again see my append.
The followings are summary.

From NF definition, NF is defined as NF=1+Te/T0,
where T0 is reference temperature(=port temperature)  
and Te is equivalent noise temperature of DUT
(Te is dependent on analysis temperature(=Tambient)).  
Standard T0 is 290K.

In sp analysis of ADS, ADS treats port temperature as 290[K] even if you set any value as port temperature.
While in Spectre, user can set any tempereture value in port but it's default(blank) value is 290K.
So in Spectre, port temperature should be 290K or blank.
In both ADS and Spectre, user can set any value as analysis temperature(Tambient).
http://www.designers-guide.org/Forum/YaBB.pl?num=1190112138

Actual NF meter with correct setting also calculates NF as T0=290K regardless of Tambient.
http://cp.literature.agilent.com/litweb/pdf/5952-3706E.pdf

[Conclusion]
The following three are all matched, that is, NF=1+Te/T0, T0=290[K] regardless of analysis temperature(Tambient).
(1) Actual NF meter with correct setting
(2) Agilent ADS NF
(3) Cadence Spectre NF with 290K or blank as port temperature

In simulation, analysis temperature means temperature of DUT.
In actual measurement, analysis temperature means ambient temperature which is almost same as temperature of DUT.

Hi,
I think that all noise due to the channel it's just putted in the antenna temperature, To=290 it's an standard used since Friis paper I think, it's like talking about why a meter is a meter. NF is a convention so all the designs can be compared in equality.

Hi,
The system requirements are dictated by the link budget given a modulation,necessary Eb/No for a given BER is obtained,the you can calculate the SNR at the input of the demodulator, from here you can obtain NF of the receiver. You must fullfill the requirement over the expected range of temperature, as pancho said:
Quote:
,the DUT noise obviously will vary with temperature,but To it's standarized to 290.