TABLE OF CONTENTS The analysis of noise in nonautonomous circuits is not unlike the calculation of conversion loss in a mixer. A conversion matrix is used to linearize the circuit around its large-signal operating conditions, and the small-signal noise is treated as an excitation. We must find the correlation matrix of the noise at the output port; the mean-square noise output voltage or current is simply one component of that matrix. With this information, the noise output power is easily calculated and converted, through the relations in Chapter 3, to a noise temperature or noise figure.
Figure 6.4 shows the problem we address. The figure shows a circuit, described by a nodal admittance matrix, and a number of modulated noise sources connected to some, but not necessarily all, of the nodes. We could include among these sources simple, unmodulated noise sources, such as those associated with an ordinary resistor. From (6.74), the correlation matrix of such a source is simply a diagonal. (We address the problem of including correlated linear sources momentarily.)
The correlation matrix of each source, C ip, is given by (6.72) to (6.74), where p is the port number. The complete correlation matrix of the full set of sources in Figure 6.4, C s, P, is
