48 



NOISE MEASURE 



[Ch.6 



Enl 



.0 



// 



Noise network 5 



Fig. 6.4. Noise network of a linear noisy two-terminal-pair network in general-circuit-matrix 



representation. 



6.3. Noise Measure 



The "excess-noise figure," Eq. 6.22, has the same numerator as the 

 noise parameter pr, Eq. 5.30, that we are trying to identify. The two 

 equations differ only in the subtractive term y^TPT^y in the denominator, 

 aside from the multiplicative constant kTo A/. In order to facilitate the 

 identification, we rewrite Eq. 5.30 in the form 



pT = 



rW^ 



(6.23) 



From a comparison of Eq, 6.23 with Eqs. 6.22 and 6.16, it is obvious that 



pT 



kToAf 



(6.24) 



1 - 



The expression on the right-hand side of Eq. 6.24 may now be identi- 

 fied as the noise parameter with the extremal properties corresponding to 

 the network invariants. In the cases in which the extended definition of 

 noise figure Fe coincides with the conventional noise figure F and the 

 exchangeable gain Ge is equal to the available gain G, the quantity in 

 Eq. 6.24 is identical with the noise measure, Eq. 1.3. We shall now adopt 

 this same name in the general case when Fe and Gg differ from the con- 

 ventional F and G, and denote this extended definition of noise measure 



