What is the standard temperature used for calculating noise figure of low noise amp?
Standard reference temperature in noise calculations is the room temperature = 17C = 290K
Regards,
IanP
Hi, I really think the reference temperature - the "room temperature" is 27*C (approx. 300*K) !
Regards, Mircea
for LNA noise figure, usually they use what standard temperature? 17 or 27 celcius?
thanks.
Actually:
25C=298.15K and 290 K= 16.85 C.
I think there is confusion here, 25C has always been considered room
temp. But, because 25C = 298 K some people round off to
290 instead of 300 K.
16.85 C ~ 17 C is a "cool" temp, I would say too low for room
temp.
To solve your dilemma go Google and type:
25C+noise
then do the same with
290K+noise
and you will find the answer ..
Regards,
IanP
The correct definition of Noise Figure is as follows: (From my course lecture notes by Prof. A. Atalar)
F (Noise Figure) specifies the degradiation in signal to noise ratio from input to output if the input noise is at 290K.
This definition corrects the wrong relation with F and SNR, specifying that the input noise should be at 290K. For other temperatures, an effective temperature calculation is necessary.
The reason why 290K is the standard temperature is not it is close to room temperature but the product of T0 = 290K with the Boltzman constant k=1.38 E-23 gives 400.2 E-23 which is quite useful for hand calculations etc. This comment on T0=290K also belongs to Prof. A. Atalar.
Thanks for everyone.
i want to calculate my LNA noise figure using hspice. the formula that i used is as below:
NF(dB) = 10 log( 1 + (inoise*inoise)/(4kT*Rs) )
Rs is source impedance, inoise is input reference noise current which can obtain using .noise analysis using hsipce (inoise not include noise generated by Rs).
is it the NF formula above correct?
Added after 3 minutes:
sorry... some corrections... inoise is input reference noise voltage
(which can display in output listing file using .print ac inoise command )
For amplifiers:
F = (k*T0*B*Ga + Nn)/(k*T0*B*Ga) = 1 + Nn/(k*T0*B*Ga)
where F: noise figure
k: Boltzman constant 1.38 E-23
T0: 290K
B: bandwidth
Ga: available gain
Nn: internal noise of the amplifier , fictitious input noise
Nn = k*Te*B*Ga
where Te: fictitious input noise temperature
So equavalently F = 1 + Te/T0
why use noise temperature and do not use the 50 ohm to characterize noise figure.
Noise temperature is a better way to do things when different parts of the system are at different temperatures. For instance, if you have a satellite antenna pointing at the sky, the noise temperature of the antenna is quite low. The LNA connected to it has noise measured at room temprature. So try to calculate the effective noise figure. You will find it is much easier if you do it in noise temperature.
Many papers well describe Noise Figure and Noise Temperature. I suggest Agilent AN 57-1 . It's easy to understand, very accurate, exaustive and it's often mentioned by other papers.
Topics like To=290K (by definition), NF vs Te etc. are deeply discussed.
Hi,
The above formula is correct, provided that you replace inoise with vnoise, as you have mentioned. The noise factor is given by:
F = 1 + Fe and Fe is equal to
Fe = vnoise^2/(4*k*T0*Rs*B)
with NF = 10*log(F). Moreover Te (effective temperature) of the device is equal to Fe*T0. As you see both Fe and Te are functions of the source impedance Rs. To model the noise properties of a linear two-port regardless of the source impedance, you need at least two noise sources. As long as you know Rs, you can transform these two noise sources to a single one (a noise voltage source "vnoise" in series "or" a parallel noise current source "inoise"), this leads to the definition of "Fe" I've written above.
hope this helps.
thanks to estradasphere.
i found that i don't include bandwidth in the NF formula but you had include the bandwidth in the formula. which definition is correct?
thanks to estradasphere.
i found that i don't include bandwidth in the NF formula but you had include the bandwidth in the formula. which definition is correct?