Noise Measure 



In Chap. 3, starting from the impedance-matrix representation, we 

 defined a noise matrix N^. The eigenvalues of N^ gave the extrema of 

 a scalar, pz, which was found to be the exchangeable power derived from 

 the polyterminal network under consideration by the arrangement of 

 Fig. 2.4. In Chap. 5, we defined a generalized noise matrix Ny, per- 

 taining to the general matrix representation in Eq. 5.2. The eigenvalues 

 of Nr and N^ are identical. Associated with the eigenvalues of Nr are 

 the extrema of the generalized scalar parameter pT in Eq. 5.25. Special 

 forms of Nr and px for the mixed voltage-current representation (Eqs. 5.3 

 through 5.6) were given in Eqs. 5.29 and 5.30. In the case of a two- 

 terminal-pair network, this representation reduces to the "general-circuit- 

 constant" description. Our interest in the noise performance of linear 

 amplifiers gives the two-terminal-pair case a special importance. The 

 remaining part of our work will therefore be confined to the interpre- 

 tation and study of ^r for the two-terminal-pair network in the general- 

 circuit-constant representation. 



Our problem is to find the physical operation that leads to the extrema 

 of pT, in the same manner as the operation of Fig, 2.4 led to the extrema 

 of pz. It is obvious that the operations involved in the extremization will 

 make use of lossless imbeddings, since only such operations leave the 

 eigenvalues of Ny unchanged. Variations in these imbeddings will 

 presumably produce variations in the column vector y in Eq. 5.30, and 

 lead to the extrema oi pT- 



The general-circuit-constant representation of a two-terminal-pair 

 network emphasizes its transfer characteristics. Therefore, we expect 



42 



