The transfer function analysis linearizes the circuit about the DC operating point and performs a small-signal analysis that calculates the transfer function from every independent source in the circuit to a designated output. The variable of interest at the output can be voltage or current.
You can specify the output with a pair of nodes or a probe component. Any component with two or more terminals can be a voltage probe. When there are more than two terminals, they are grouped in pairs, and you use the portv parameter to select the appropriate pair of terminals. Alternatively, you can specify a voltage to be the output by giving a pair of nodes on the xf analysis statement.
Any component that naturally computes current as an internal variable can be a current probe. If the probe component computes more than one current (as transmission lines, microstrip lines, and N-ports do), you use the porti parameter to select the appropriate current. It is an error to specify both portv and porti. If neither is specified, the probe component provides a reasonable default.
The stimuli parameter specifies the inputs for the transfer functions. There are two choices. stimuli=sources indicates that the sources present in the circuit should be used. The xfmag parameters provided by the sources may be used to adjust the computed gain to compensate for gains or losses in a test fixture. You can limit the number of sources in hierarchical netlists by using the save and nestlvl parameters.
Name [p] [n] xf parameter=value ...
The optional terminals (p and n) specify the output of the circuit. If you do not specify the terminals, you must specify the output with a probe component.